Full-fat Dairy for Cardiovascular Health

I just saw a paper in the AJCN titled "Dairy consumption and patterns of mortality of
Australian adults". It's a prospective study with a 15-year follow-up period. Here's a quote from the abstract:

There was no consistent and significant association between total dairy intake and total or cause-specific mortality. However, compared with those with the lowest intake of full-fat dairy, participants with the highest intake (median intake 339 g/day) had reduced death due to CVD (HR: 0.31; 95% confidence interval (CI): 0.12–0.79; P for trend = 0.04) after adjustment for calcium intake and other confounders. Intakes of low-fat dairy, specific dairy foods, calcium and vitamin D showed no consistent associations.

People who ate the most full-fat dairy had a 69% lower risk of cardiovascular death than those who ate the least. Otherwise stated, people who mostly avoided dairy or consumed low-fat dairy had more than three times the risk of dying of coronary heart disease or stroke than people who ate the most full-fat diary.

Contrary to popular belief, full-fat dairy, including milk, butter and cheese, has never been convincingly linked to cardiovascular disease. In fact, it has rather consistently been linked to a lower risk, particularly for stroke. What has been linked to cardiovascular disease is milk fat's replacement, margarine. In the Rotterdam study, high vitamin K2 intake was linked to a lower risk of fatal heart attack, aortic calcification and all-cause mortality. Most of the K2 came from full-fat cheese. In my opinion, artisanal cheese and butter made from pasture-fed milk are the ultimate dairy foods.

From a 2005 literature review on milk and cardiovascular disease in the EJCN:

In total, 10 studies were identified. Their results show a high degree of consistency in the reported risk for heart disease and stroke, all but one study suggesting a relative risk of less than one in subjects with the highest intakes of milk.

...the studies, taken together, suggest that milk drinking may be associated with a small but worthwhile reduction in heart disease and stroke risk.

...All the cohort studies in the present review had, however, been set up at times when reduced-fat milks were unavailable, or scarce.

The fat is where the vitamins A, K2, E and D are. The fat is where the medium-chain triglycerides, butyric acid and omega-3 fatty acids are. The fat is where the conjugated linoleic acid is. So the next time someone admonishes you to reduce your dairy fat intake, what are you going to tell them??

Copper and Cardiovascular Disease

In 1942, Dr. H. W. Bennetts dissected 21 cattle known to have died of "falling disease". This was the name given to the sudden, inexplicable death that struck herds of cattle in certain regions of Australia. Dr. Bennett believed the disease was linked to copper deficiency. He found that 19 of the 21 cattle had abnormal hearts, showing atrophy and abnormal connective tissue infiltration (fibrosis) of the heart muscle (1).

In 1963, Dr. W. F. Coulson and colleagues found that 22 of 33 experimental copper-deficient pigs died of cardiovascular disease. 11 of 33 died of coronary heart disease, the quintessential modern human cardiovascular disease. Pigs on a severely copper-deficient diet showed weakened and ruptured arteries (aneurysms), while moderately deficient pigs "survived with scarred vessels but demonstrated a tendency toward premature atherosclerosis" including foam cell accumulation (2). Also in 1963, Dr. C. R. Ball and colleagues published a paper describing blood clots in the heart and coronary arteries, heart muscle degeneration, ventricular calcification and early death in mice fed a lard-rich diet (3).

This is where Dr. Leslie M. Klevay enters the story. Dr. Klevay suspected that Ball's mice had suffered from copper deficiency, and decided to test the hypothesis. He replicated Ball's experiment to the letter, using the same strain of mice and the same diet. Like Ball, he observed abnormal clotting in the heart, degeneration and enlargement of the heart muscle, and early death. He also showed by electrocardiogram that the hearts of the copper-deficient mice were often contracting abnormally (arrhythmia).

But then the coup de grace: he prevented these symptoms by supplementing the drinking water of a second group of mice with copper (4). In the words of Dr. Klevay: "copper was an antidote to fat intoxication" (5). I believe this was his tongue-in-cheek way of saying that the symptoms had been misdiagnosed by Ball as due to dietary fat, when in fact they were due to a lack of copper.

Since this time, a number of papers have been published on the relationship between copper intake and cardiovascular disease in animals, including several showing that copper supplementation prevents atherosclerosis in one of the most commonly used animal models of cardiovascular disease (6, 7, 8). Copper supplementation also corrects abnormal heart enlargement-- called hypertrophic cardiomyopathy-- and heart failure due to high blood pressure in mice (9).

For more than three decades, Dr. Klevay has been a champion of the copper deficiency theory of cardiovascular disease. According to him, copper deficiency is the only single intervention that has caused the full spectrum of human cardiovascular disease in animals, including:

• Heart attacks (myocardial infarction)
  
• Blood clots in the coronary arteries and heart
• Fibrous atherosclerosis including smooth muscle proliferation
• Unstable blood vessel plaque
  
• Foam cell accumulation and fatty streaks
  
• Calcification of heart tissues
  
• Aneurysms (ruptured vessels)
• Abnormal electrocardiograms
• High cholesterol
• High blood pressure
  

If this theory is so important, why have most people never heard of it? I believe there are at least three reasons. The first is that the emergence of the copper deficiency theory coincided with the rise of the diet-heart hypothesis, whereby saturated fat causes heart attacks by raising blood cholesterol. Bolstered by some encouraging findings and zealous personalities, this theory took the Western medical world by storm, for decades dominating all other theories in the medical literature and public health efforts. My opinions on the diet-heart hypothesis aside, the two theories are not mutually exclusive.

The second reason you may not have heard of the theory is due to a lab assay called copper-mediated LDL oxidation. Researchers take LDL particles (from blood, the same ones the doctor measures as part of a cholesterol test) and expose them to a high concentration of copper in a test tube. Free copper ions are oxidants, and the researchers then measure the amount of time it takes the LDL to oxidize. I find this assay tiresome, because studies have shown that the amount of time it takes copper to oxidize LDL in a test tube doesn't predict how much oxidized LDL you'll actually find in the bloodstream of the person you took the LDL from (10, 11).

In other words, it's an assay that has little bearing on real life. But researchers like it because for some odd reason, feeding a person saturated fat causes their LDL to be oxidized more rapidly by copper in a test tube, even though that's not the case in the actual bloodstream (12). Guess which result got emphasized?

The fact that copper is such an efficient oxidant has led some researchers to propose that copper oxidizes LDL in human blood, and therefore dietary copper may contribute to heart disease (oxidized LDL is a central player in heart disease-- read more here). The problem with this theory is that there are virtually zero free copper ions in human serum. Then there's the fact that supplementing humans with copper actually reduces the susceptibility of red blood cells to oxidation (by copper in a test tube, unfortunately), which is difficult to reconcile with the idea that dietary copper increases oxidative stress in the blood (13).

The third reason you may never have heard of the theory is more problematic. Several studies have found that a higher level copper in the blood correlates with a higher risk of heart attack (14, 15). At this point, I could hang up my hat, and declare the animal experiments irrelevant to humans. But let's dig deeper.

Nutrient status is sometimes a slippery thing to measure. As it turns out, serum copper isn't a good marker of copper status. In a 4-month trial of copper depletion in humans, blood copper stayed stable, while the activity of copper-dependent enzymes in the blood declined (16). These include the important copper-dependent antioxidant, superoxide dismutase. As a side note, lysyl oxidase is another copper-dependent enzyme that cross-links the important structural proteins collagen and elastin in the artery wall, potentially explaining some of the vascular consequences of copper deficiency. Clotting factor VIII increased dramatically during copper depletion, perhaps predicting an increased tendency to clot. Even more troubling, three of the 12 women developed heart problems during the trial, which the authors felt was unusual:

We observed a significant increase over control values in the number of ventricular premature discharges (VPDs) in three women after 21, 63, and 91 d of consuming the low-copper diet; one was subsequently diagnosed as having a second-degree heart block.

In another human copper restriction trial, 11 weeks of modest copper restriction coincided with heart trouble in 4 out of 23 subjects, including one heart attack (17):

In the history of conducting numerous human studies at the Beltsville Human Nutrition Research Center involving participation by 337 subjects, there had previously been no instances of any health problem related to heart function. During the 11 wk of the present study in which the copper density of the diets fed the subjects was reduced from the pretest level of 0.57 mg/ 1000 kcal to 0.36 mg/1000 kcal, 4 out of 23 subjects were diagnosed as having heart-related abnormalities.

The other reason to be skeptical of the association between blood copper and heart attack risk is that inflammation increases copper in the blood (18, 19). Blood copper level correlates strongly with the marker of inflammation C-reactive protein (CRP) in humans, yet substantially increasing copper intake doesn't increase CRP (20, 21). This suggests that elevated blood copper is likely a symptom of inflammation, rather than its cause, and presents an explanation for the association between blood copper level and heart attack risk.

Only a few studies have looked at the relationship between more accurate markers of copper status and cardiovascular disease in humans. Leukocyte copper status, a marker of tissue status, is lower in people with cardiovascular disease (22, 23). People who die of heart attacks generally have less copper in their hearts than people who die of other causes, although this could be an effect rather than a cause of the heart attack (24). Overall, I find the human data lacking. I'd like to see more studies examining liver copper status in relation to cardiovascular disease, as the liver is the main storage organ for copper.

According to a 2001 study, the majority of Americans may have copper intakes below the USDA recommended daily allowance (25), many substantially so. This problem is exacerbated by the fact that copper levels in food have declined in industrial nations over the course of the 20th century, something I'll discuss in the next post.

New Review of Controlled Trials Replacing Saturated fat with Industrial Seed Oils

Readers Stanley and JBG just informed me of a new review paper by Dr. Dariush Mozaffarian and colleagues. Dr. Mozaffarian is one of the Harvard epidemiologists responsible for the Nurse's Health study. The authors claim that overall, the controlled trials show that replacing saturated fat with polyunsaturated fat from industrial seed oils, but not carbohydrate or monounsaturated fat (as in olive oil), slightly reduces the risk of having a heart attack:

These findings provide evidence that consuming PUFA in place of SFA reduces CHD events in RCTs [how do you like the acronyms?]. This suggests that rather than trying to lower PUFA consumption, a shift toward greater population PUFA consumption in place of SFA would significantly reduce rates of CHD.

Looking at the studies they included in their analysis (and at those they excluded), it looks like they did a very nice job cherry picking. For example:

• They included the Finnish Mental Hospital trial, which is a terrible trial for a number of reasons. It wasn't randomized, appropriately controlled or even semi-blinded*. Thus, it doesn't fit the authors' stated inclusion criteria, but they included it in their analysis anyway**. Besides, the magnitude of the result has never been replicated by better trials, not even close.
  
• They included two trials that changed more than just the proportion of SFA to PUFA. For example, the Oslo Diet-heart trial replaced animal fat with seed oils, but also increased fruit, nut, vegetable and fish intake, while reducing trans fat margarine intake! The STARS trial increased both omega-6 and omega-3, reduced processed food intake, and increased fruit and vegetable intake! These obviously aren't controlled trials isolating the issue of dietary fat substitution. If you subtract the four inappropriate trials from their analysis, which is half the studies they analyzed, the result disappears. Those four just happened to show the largest reduction in heart attack mortality...
  
• They excluded the Rose et al. corn oil trial and the Sydney Diet-heart trial. Both found a large increase in total mortality from replacing animal fat with seed oils, and the Rose trial found a large increase in heart attack deaths (the Sydney trial didn't report CHD deaths, but Dr. Mozaffarian et al. stated in their paper that they contacted authors to obtain unpublished results. Why didn't they contact the authors of this study?).

The authors claim, based on their analysis, that replacing 5% of calories as saturated fat with polyunsaturated fat would reduce the risk of having a heart attack by 10%. Take a minute to think about the implications of that statement. For the average American, that means cutting saturated fat nearly in half to 6% of energy, which is a real challenge if you want to have a semblance of a normal diet. It also means nearly doubling PUFA intake, which will come mostly from seed oils if you follow the authors' advice.

So basically, even if the authors' conclusion were correct, you overhaul your whole diet and replace natural foods with bland unnatural foods, and...? You reduce your 10-year risk of having a heart attack from 10 percent to 9 percent. Without affecting your overall risk of dying! The paper states that the interventions didn't affect overall mortality at all. That's what they're talking about here. Sign me up!


* Autopsies were not conducted in a blinded manner. Physicians knew which hospital the cadavers came from, because autopsies were done on-site. There is some confusion about this point because the second paper states that physicians interpreted the autopsy reports in a blinded manner. But that doesn't make it blinded, since the autopsies weren't blinded. The patients were also not blinded, so the study overall was highly susceptible to bias.

** They refer to it as "cluster randomized". I don't know if that term accurately applies to the Finnish trial or not. The investigators definitely didn't randomize the individual patients: whichever hospital a person was being treated in, that's the food he/she ate. There were only two hospitals, so "cluster randomization" in this case would just refer to deciding which hospital got the intervention first. Can this accurately be called randomized?

Fatty Liver: It's not Just for Grown-ups Anymore

The epidemic of non-alcoholic fatty liver disease (NAFLD) is one of my favorite topics on this blog, due to the liver's role as the body's metabolic "grand central station", as Dr. Philip Wood puts it. The liver plays a critical part in the regulation of sugar, insulin, and lipid levels in the blood. Many of the routine blood tests administered in the doctor's office (blood glucose, cholesterol, etc.) partially reflect liver function.

NAFLD is an excessive accumulation of fat in the liver that impairs its function and can lead to severe liver inflammation (NASH), and in a small percentage of people, liver cancer. An estimated 20-30% of people in industrial nations suffer from NAFLD, a shockingly high prevalence (1).

I previously posted on dietary factors I believe are involved in NAFLD. In rodents, feeding a large amount of sugar or industrial seed oils (corn oil, etc.) promotes NAFLD, whereas fats such as butter and coconut oil do not (2). In human infants, enteric feeding with industrial seed oils causes severe liver damage, whereas the same amount of fat from fish oil doesn't, and can even reverse the damage done by seed oils (3).

So basically, I think sugar and industrial oils are major contributors to NAFLD, and if you look at diet trends in the US over the last 40 years, they're consistent with the idea. Industrial oils are harmful due (at least in part) to their high omega-6 content, which is problematic partially because it disturbs normal omega-3 metabolism. A potential solution to fatty liver is to reduce sugar, replace industrial oils with natural fats, and ensure a regular source of omega-3. I've posted two anecdotes of people rapidly healing their fatty livers using diet changes* (4, 5).

I recently came across a study that examined the diet of Canadian children with NAFLD (6). The children had a high sugar intake, a typical (i.e., high) omega-6 intake, and a low omega-3 intake. The authors claimed that the children also had a high saturated fat intake, but at 10.5% of calories, they were almost eating to the American Heart Association's "Step I" diet recommendations**. Busted! Total fat intake was also low.

High sugar consumption was associated with a larger waist circumference, insulin resistance, lower adiponectin and elevated markers of inflammation. High omega-6 intake was associated with markers of inflammation. Low omega-3 intake was associated with insulin resistance and elevated liver enzymes. Saturated fat intake presumably had no relation to any of these markers, since they didn't mention it in the text.

These children with NAFLD, who were all insulin resistant and mostly obese, had diets high in omega-6, high in sugar, and low in omega-3. This is consistent with the idea that these three factors, which have all been moving in the wrong direction in the last 40 years, contribute to NAFLD.


* Fatty liver was assessed by liver enzymes, admittedly not a perfect test. However, elevated liver enzymes do correlate fairly well with NAFLD.

** Steps I and II were replaced by new diet advice in 2000. The AHA now recommends keeping saturated fat below 7% of calories. Stock up on those skinless chicken breasts! Make sure there isn't any residual fat sticking to the meat, it might kill you. I do have to give the AHA credit however, because their new recommendations focus mostly on eating real food rather than avoiding saturated fat and cholesterol.

Book Review: The Primal Blueprint

Mark Sisson has been a central figure in the evolutionary health community since he began his weblog Mark's Daily Apple in 2006. He and his staff have been posting daily on his blog ever since. He has also written several other books, edited the Optimum Health newsletter, competed as a high-level endurance athlete, and served on the International Triathlon Union as the anti-doping chairman, all of which you can read about on his biography page. Mark is a practice-what-you-preach kind of guy, and if physical appearance means anything, he's on to something.

In 2009, Mark published his long-awaited book The Primal Blueprint. He self-published the book, which has advantages and disadvantages. The big advantage is that you aren't subject to the sometimes onerous demands of publishers, who attempt to maximize sales at Barnes and Noble. The front cover sports a simple picture of Mark, rather than a sunbaked swimsuit model, and the back cover offers no ridiculous claims of instant beauty and fat loss.

The drawback of self-publishing is it's more difficult to break into a wider market. That's why Mark has asked me to publish my review of his book today. He's trying to push it up in the Amazon.com rankings so that it gets a broader exposure. If you've been thinking about buying Mark's book, now is a good time to do it. If you order it from Amazon.com on March 17th, Mark is offering to sweeten the deal with some freebies on his site Mark's Daily Apple. Full disclosure: I'm not getting anything out of this, I'm simply mentioning it because I was reviewing Mark's book anyway and I thought some readers might enjoy it.

The Primal Blueprint is not a weight loss or diet book, it's a lifestyle program with an evolutionary slant. Mark uses the example of historical and contemporary hunter-gatherers as a model, and attempts to apply those lessons to life in the 21st century. He does it in a way that's empowering accessible to nearly everyone. To illustrate his points, he uses the example of an archetypal hunter-gatherer called Grok, and his 21st century mirror image, the Korg family.

The diet section will be familiar to anyone who has read about "paleolithic"-type diets. He advocates eating meats including organs, seafood, eggs, nuts, abundant vegetables, and fruit. He also suggests avoiding grains, legumes, dairy (although he's not very militant about this one), processed food in general, and reducing carbohydrate to less than 150 grams per day. I like his diet suggestions because they focus on real food. Mark is not a drill sergeant. He tries to create a plan that will be sustainable in the long run, by staying positive and allowing for cheats.

We part ways on the issue of carbohydrate. He suggests that eating more than 150 grams of carbohydrate per day leads to fat gain and disease, whereas I feel that position is untenable in light of what we know of non-industrial cultures (including some relatively high-carbohydrate hunter-gatherers). Although carbohydrate restriction (or at least wheat and sugar restriction) does have its place in treating obesity and metabolic dysfunction in modern populations, ultimately I don't think it's necessary for the prevention of those same problems, and it can even be counterproductive in some cases. Mark does acknowledge that refined carbohydrates are the main culprits.

The book's diet section also recommends nutritional supplements, including a multivitamin/mineral, antioxidant supplement, probiotics, protein powder and fish oil. I'm not a big proponent of supplementation. I'm also a bit of a hypocrite because I do take small doses of fish oil (when I haven't had seafood recently), and vitamin D in wintertime. But I can't get behind protein powders and antioxidant supplements.

Mark's suggestions for exercise, sun exposure, sleep and stress management make good sense to me. In a nutshell: do all three, but keep the exercise varied and don't overdo it. As a former high-level endurance athlete, he has a lot of credibility here. He puts everything in a format that's practical, accessible and empowering.

I think The Primal Blueprint is a useful book for a person who wants to maintain or improve her health. Although we disagree on the issue of carbohydrate, the diet and lifestyle advice is solid and will definitely be a vast improvement over what the average person is doing. The Primal Blueprint is not an academic book, nor does it attempt to be. It doesn't contain many references (although it does contain some), and it won't satisfy someone looking for an in-depth discussion of the scientific literature. However, it's perfect for someone who's getting started and needs guidance, or who simply wants a more comprehensive source than reading blog snippets. It would make a great gift for that family member or friend who's been asking how you stay in such good shape.

Corn Oil and Cancer: Reality Strikes Again

The benefits of corn oil keep rolling in. In a new study by Stephen Freedland's group at Duke, feeding mice a diet rich in butter and lard didn't promote the growth of transplanted human prostate cancer cells any more than a low-fat diet (1).

Why do we care? Because other studies, including one from the same investigators, show that corn oil and other industrial seed oils strongly promote prostate cancer cell growth and increase mortality in similar models (2, 3).

From the discussion section:

Current results combined with our prior results suggest that lowering the fat content of a primarily saturated fat diet offers little survival benefit in an intact or castrated LAPC-4 xenograft model. In contrast to the findings when omega-6 fats are used, these results raise the possibility that fat type may be as important as fat amount or perhaps even more important.

The authors seem somewhat surprised and pained by the result. Kudos for publishing it. However, there's nothing to be surprised about. There's a large body of evidence implicating excess omega-6 fat in a number of cancer models. Reducing omega-6 to below 4% of calories has a dramatic effect on cancer incidence and progression*. In fact, there have even been several experiments showing that butter and other animal fats promote cancer growth to a lesser degree than margarine and omega-6-rich seed oils. I discussed that here.

I do have one gripe with the study. They refer to the diet as "saturated fat based". That's inaccurate terminology. I see it constantly in the diet-health literature. If it were coconut oil, then maybe I could excuse it, because coconut fat is 93% saturated. But this diet was made of lard and butter, the combination of which is probably about half saturated. The term "animal fat" or "low-omega-6 fat" would have been more accurate. At least they listed the diet composition. Many studies don't even bother, leaving it to the reader to decide what they mean by "saturated fat".


* The average American eats 7-8% omega-6 by calories. This means it will be difficult to see a relationship between omega-6 intake and cancer (or heart disease, or most things) in observational studies in the US or other industrial nations, because we virtually all eat more than 4% of calories as omega-6. Until the 20th century, omega-6 intake was below 4%, and usually closer to 2%, in most traditional societies. That's where it remains in contemporary traditional societies unaffected by industrial food habits, such as Kitava. Our current omega-6 intake is outside the evolutionary norm.

Magnesium and Insulin Sensitivity

From a paper based on US NHANES nutrition and health survey data (1):

During 1999–2000, the diet of a large proportion of the U.S. population did not contain adequate magnesium... Furthermore, racial or ethnic differences in magnesium persist and may contribute to some health disparities.... Because magnesium intake is low among many people in the United States and inadequate magnesium status is associated with increased risk of acute and chronic conditions, an urgent need exists to perform a current survey to assess the physiologic status of magnesium in the U.S. population.

Magnesium is an essential mineral that's slowly disappearing from the modern diet, as industrial agriculture and industrial food processing increasingly dominate our food choices. One of the many things it's necessary for in mammals is proper insulin sensitivity and glucose control. A loss of glucose control due to insulin resistance can eventually lead to diabetes and all its complications.

Magnesium status is associated with insulin sensitivity (2, 3), and a low magnesium intake predicts the development of type II diabetes in most studies (4, 5) but not all (6). Magnesium supplements largely prevent diabetes in a rat model* (7). Interestingly, excess blood glucose and insulin themselves seem to reduce magnesium status, possibly creating a vicious cycle.

In a 1993 trial, a low-magnesium diet reduced insulin sensitivity in healthy volunteers by 25% in just four weeks (8). It also increased urinary thromboxane concentration, a potential concern for cardiovascular health**.

At least three trials have shown that magnesium supplementation increases insulin sensitivity in insulin-resistant diabetics and non-diabetics (9, 10, 11). In some cases, the results were remarkable. In type II diabetics, 16 weeks of magnesium supplementation improved fasting glucose, calculated insulin sensitivity and HbA1c*** (12). HbA1c dropped by 22 percent.

In insulin resistant volunteers with low blood magnesium, magnesium supplementation for four months reduced estimated insulin resistance by 43 percent and decreased fasting insulin by 32 percent (13). This suggests to me that magnesium deficiency was probably one of the main reasons they were insulin resistant in the first place. But the study had another very interesting finding: magnesium improved the subjects' blood lipid profile remarkably. Total cholesterol decreased, LDL decreased, HDL increased and triglycerides decreased by a whopping 39 percent. The same thing had been reported in the medical literature decades earlier when doctors used magnesium injections to treat heart disease, and also in animals treated with magnesium. Magnesium supplementation also suppresses atherosclerosis (thickening and hardening of the arteries) in animal models, a fact that I may discuss in more detail at some point (14, 15).

In the previous study, participants were given 2.5 g magnesium chloride (MgCl2) per day. That's a bit more than the USDA recommended daily allowance (MgCl2 is mostly chloride by weight), in addition to what they were already getting from their diet. Most of a person's magnesium is in their bones, so correcting a deficiency by eating a nutritious diet may take a while.

Speaking of nutritious diets, how does one get magnesium? Good sources include halibut, leafy greens, chocolate and nuts. Bone broths are also an excellent source of highly absorbable magnesium. Whole grains and beans are also fairly good sources, while refined grains lack most of the magnesium in the whole grain. Organic foods, particularly artisanally produced foods from a farmer's market, are richer in magnesium because they grow on better soil and often use older varieties that are more nutritious.

The problem with seeds such as grains, beans and nuts is that they also contain phytic acid which prevents the absorption of magnesium and other minerals (16). Healthy non-industrial societies that relied on grains took great care in their preparation: they soaked them, often fermented them, and also frequently removed a portion of the bran before cooking (17). These steps all served to reduce the level of phytic acid and other anti-nutrients. I've posted a method for effectively reducing the amount of phytic acid in brown rice (18). Beans should ideally be soaked for 24 hours before cooking, preferably in warm water.

Industrial agriculture has systematically depleted our soil of many minerals, due to high-yield crop varieties and the fact that synthetic fertilizers only replace a few minerals. The mineral content of foods in the US, including magnesium, has dropped sharply in the last 50 years. The reason we need to use fertilizers in the first place is that we've broken the natural nutrient cycle in which minerals always return to the soil in the same place they were removed. In 21st century America, minerals are removed from the soil, pass through our toilets, and end up in the landfill or in waste water. This will continue until we find an acceptable way to return human feces and urine to agricultural soil, as many cultures do to this day****.

I believe that an adequate magnesium intake is critical for proper insulin sensitivity and overall health.


* Zucker rats that lack leptin signaling

** Thromboxane A2 is an omega-6 derived eicosanoid that potently constricts blood vessels and promotes blood clotting. It's interesting that magnesium has such a strong effect on it. It indicates that fatty acid balance is not the only major influence on eicosanoid production.

*** Glycated hemoglobin. A measure of the average blood glucose level over the past few weeks.

**** Anyone interested in further reading on this should look up The Humanure Handbook

Lindeberg on Obesity

I'm currently reading Dr. Staffan Lindeberg's magnum opus Food and Western Disease, recently published in English for the first time. Dr. Lindeberg is one of the world's leading experts on the health and diet of non-industrial cultures, particularly in Papua New Guinea. The book contains 2,034 references. It's also full of quotable statements. Here's what he has to say about obesity:

Middle-age spread is a normal phenomenon - assuming you live in the West. Few people are able to maintain their [youthful] waistline after age 50. The usual explanation - too little exercise and too much food - does not fully take into account the situation among traditional populations. Such people are usually not as physically active as you may think, and they usually eat large quantities of food.

Overweight has been extremely rare among hunter-gatherers and other traditional cultures [18 references]. This simple fact has been quickly apparent to all foreign visitors...

The Kitava study measured height, weight, waist circumference, subcutaneous fat thickness at the back of the upper arm (triceps skinfold) and upper arm circumference on 272 persons ages 4-86 years. Overweight and obesity were absent and average [body mass index] was low across all age groups. ...no one was larger around their waist than around their hips.

...The circumference of the upper arm [mostly indicating muscle mass] was only negligibly smaller on Kitava [compared with Sweden], which indicates that there was no malnutrition. It is obvious from our investigations that lack of food is an unknown concept, and that the surplus of fruits and vegetables regularly rots or is eaten by dogs.

The Population of Kitava occupies a unique position in the world in terms of the negligible effect that the Western lifestyle has had on the island.

The only obese Kitavans Dr. Lindeberg observed were two people who had spent several years off the island living a modern, urban lifestyle, and were back on Kitava for a visit.

I'd recommend this book to anyone who has a scholarly interest in health and nutrition, and somewhat of a background in science and medicine. It's extremely well referenced, which makes it much more valuable.

Dissolve Away those Pesky Bones with Corn Oil

I just read an interesting paper from Gabriel Fernandes's group at the University of Texas. It's titled "High fat diet-induced animal model of age-associated obesity and osteoporosis". I was expecting this to be the usual "we fed mice industrial lard for 60% of calories and they got sick" paper, but I was pleasantly surprised. From the introduction:

CO [corn oil] is known to promote bone loss, obesity, impaired glucose tolerance, insulin resistance and thus represents a useful model for studying the early stages in the development of obesity, hyperglycemia, Type 2 diabetes [23] and osteoporosis. We have used omega-6 fatty acids enriched diet as a fat source which is commonly observed in today's Western diets basically responsible for the pathogenesis of many diseases [24].

Just 10% of the diet as corn oil (roughly 20% of calories), with no added omega-3, on top of an otherwise poor laboratory diet, caused:

• Obesity
• Osteoporosis
• The replacement of bone marrow with fat cells
  
• Diabetes
• Insulin resistance
  
• Generalized inflammation
• Elevated liver weight (possibly indicating fatty liver)
  

Hmm, some of these sound familiar... We can add them to the findings that omega-6 also promotes various types of cancer in rodents (1).

20% fat is less than the amount it typically takes to make a rodent this sick. This leads me to conclude that corn oil is particularly good at causing mouse versions of some of the most common facets of the "diseases of civilization". It's exceptionally high in omega-6 (linoleic acid) with virtually no omega-3.

Make sure to eat your heart-healthy corn oil! It's made in the USA, dirt cheap and it even lowers cholesterol!

Saturated Fat and Insulin Sensitivity

Insulin sensitivity is a measure of the tissue response to insulin. Typically, it refers to insulin's ability to cause tissues to absorb glucose from the blood. A loss of insulin sensitivity, also called insulin resistance, is a core part of the metabolic disorder that affects many people in industrial nations.

I don't know how many times I've seen the claim in journal articles and on the internet that saturated fat reduces insulin sensitivity. The idea is that saturated fat reduces the body's ability to handle glucose effectively, placing people on the road to diabetes, obesity and heart disease. Given the "selective citation disorder" that plagues the diet-health literature, perhaps this particular claim deserves a closer look.

The Evidence

I found a review article from 2008 that addressed this question (1). I like this review because it only includes high-quality trials that used reliable methods of determining insulin sensitivity*.

On to the meat of it. There were 5 studies in which non-diabetic people were fed diets rich in saturated fat, and compared with a group eating a diet rich in monounsaturated (like olive oil) or polyunsaturated (like corn oil) fat. They ranged in duration from one week to 3 months. Four of the five studies found that fat quality did not affect insulin sensitivity, including one of the 3-month studies.

The fifth study, which is the one that's nearly always cited in the diet-health literature, requires some discussion. This was the KANWU study (2). Over the course of three months, investigators fed 163 volunteers a diet rich in either saturated fat or monounsaturated fat.

The SAFA diet included butter and a table margarine containing a relatively high proportion of SAFAs. The MUFA diet included a spread and a margarine containing high proportions of oleic acid derived from high-oleic sunflower oil and negligible amounts of trans fatty acids and n-3 fatty acids and olive oil.

Yummy. After three months of these diets, there was no significant difference in insulin sensitivity between the saturated fat group and the monounsaturated fat group. Yes, you read that right. Even the study that's selectively cited as evidence that saturated fat causes insulin resistance found no significant difference between the diets. You might not get this by reading the misleading abstract. I'll be generous and acknowledge that the (small) difference was almost statistically significant (p = 0.053).

What the authors decided to focus on instead is the fact that insulin sensitivity declined slightly but significantly on the saturated fat diet compared with the pre-diet baseline. That's why this study is cited as evidence that saturated fat impairs insulin sensitivity. But anyone who has a basic science background will see where this reasoning is flawed (warning: nerd attack. skip the rest of the paragraph if you're not interested). You need a control group for comparison, to take into account normal fluctuations caused by such things as the season, eating mostly cafeteria food, and having a doctor hooking you up to machines. That control group was the group eating monounsaturated fat. The comparison between diet groups was the 'primary outcome', in statistics lingo. That's the comparison that matters, and it wasn't significant. To interpret the study otherwise is to ignore the basic conventions of statistics, which the authors were happy to do. There's a name for it: 'moving the goalpost'. The reviewers shouldn't have let this kind of shenanigans slide.

So we have five studies through 2008, none of which support the idea that saturated fat reduces insulin sensitivity in non-diabetics. Since the review paper was published, I know of one subsequent study that asked the same question (3). Susan J. van Dijk and colleagues fed volunteers with abdominal overweight (beer gut) a diet rich in either saturated fat or monounsaturated fat. I e-mailed the senior author and she said the saturated fat diet was "mostly butter". The specific fats used in the diets weren't mentioned anywhere in the paper, which is a major omission**. In any case, after 8 weeks, insulin sensitivity was virtually identical between the two groups. This study appeared well controlled and used the gold standard method for assessing insulin sensitivity, called the euglycemic-hyperinsulinemic clamp technique***.

The evidence from controlled trials is rather consistent that saturated fat has no appreciable effect on insulin sensitivity.

Why Are We so Focused on Saturated Fat?

Answer: because it's the nutrient everyone loves to hate. As an exercise in completeness, I'm going to mention three dietary factors that actually reduce insulin sensitivity, and get a lot less air time than saturated fat.

#1: Caffeine. That's right, controlled trials show that your favorite murky beverage reduces insulin sensitivity (4, 5). Is it actually relevant to real life? I doubt it. The doses used were large and the studies short-term.

#2: Magnesium deficiency. A low-magnesium diet reduced insulin sensitivity by 25% over the course of three weeks (6). I think this is probably relevant to long-term insulin sensitivity and overall health, although it would be good to have longer-term data. Magnesium deficiency is widespread in industrial nations, due to our over-reliance on refined foods such as sugar, white flour and oils.

#3: Sugar. Fructose reduces insulin sensitivity in humans, along with many other harmful effects (7).

As long as we continue to focus our energy on indicting saturated fat, it will continue distracting us from the real causes of disease.


* For the nerds: euglycemic-hyperinsulinemic clamp (the gold standard), insulin suppression test, or intravenous glucose tolerance test with Minimal Model. They didn't include studies that reported HOMA as their only measure, because it's not very accurate.

** There's this idea that pervades the diet-health literature that all saturated fats are roughly equivalent, all monounsaturated fats are equivalent, etc., therefore it doesn't matter what the source was. This is beyond absurd and reflects our cultural obsession with saturated fat. It really irks me that the reviewers didn't demand this information.

*** They did find that markers of inflammation in fat tissue were higher after the saturated fat diet.

The Body Fat Setpoint, Part IV: Changing the Setpoint

Prevention is Easier than Cure

Experiments in animals have confirmed what common sense suggests: it's easier to prevent health problems than to reverse them. Still, many health conditions can be improved, and in some cases reversed, through lifestyle interventions. It's important to have realistic expectations and to be kind to oneself. Cultivating a drill sergeant mentality will not improve quality of life, and isn't likely to be sustainable.

Fat Loss: a New Approach

If there's one thing that's consistent in the medical literature, it's that telling people to eat fewer calories does not help them lose weight in the long term. Gary Taubes has written about this at length in his book Good Calories, Bad Calories, and in his upcoming book on body fat. Many people who use this strategy see transient fat loss, followed by fat regain and a feeling of defeat. There's a simple reason for it: the body doesn't want to lose weight. It's extremely difficult to fight the fat mass setpoint, and the body will use every tool it has to maintain its preferred level of fat: hunger, reduced body temperature, higher muscle efficiency (i.e., less energy is expended for the same movement), lethargy, lowered immune function, et cetera.

Therefore, what we need for sustainable fat loss is not starvation; we need a treatment that lowers the fat mass setpoint. There are several criteria that this treatment will have to meet to qualify:

1. It must cause fat loss
2. It must not involve deliberate calorie restriction
3. It must maintain fat loss over a long period of time
4. It must not be harmful to overall health
   

I also prefer strategies that make sense from the perspective of human evolution.

Strategies: Diet Pattern

The most obvious treatment that fits all of my criteria is low-carbohydrate dieting. Overweight people eating low-carbohydrate diets generally lose fat and spontaneously reduce their calorie intake. In fact, in several diet studies, investigators compared an all-you-can-eat low-carbohydrate diet with a calorie-restricted low-fat diet. The low-carbohydrate dieters generally reduced their calorie intake and body fat to a similar or greater degree than the low-fat dieters, despite the fact that they ate all the calories they wanted (1). This suggest that their fat mass setpoint had changed. At this point, I think moderate carbohydrate restriction may be preferable to strict carbohydrate restriction for some people, due to the increasing number of reports I've read of people doing poorly in the long run on extremely low-carbohydrate diets (2).

Another strategy that appears effective is the "paleolithic" diet. In Dr. Staffan Lindeberg's 2007 diet study, overweight volunteers with heart disease lost fat and reduced their calorie intake to a remarkable degree while eating a diet consistent with our hunter-gatherer heritage (3). This result is consistent with another diet trial of the paleolithic diet in diabetics (4). In post hoc analysis, Dr. Lindeberg's group showed that the reduction in weight was apparently independent of changes in carbohydrate intake*. This suggests that the paleolithic diet has health benefits that are independent of carbohydrate intake.

Strategies: Gastrointestinal Health

Since the gastrointestinal (GI) tract is so intimately involved in body fat metabolism and overall health (see the former post), the next strategy is to improve GI health. There are a number of ways to do this, but they all center around four things:

1. Don't eat food that encourages the growth of harmful bacteria
2. Eat food that encourages the growth of good bacteria
3. Don't eat food that impairs gut barrier function
4. Eat food that promotes gut barrier health

The first one is pretty easy: avoid refined sugar, refined carbohydrate in general, and lactose if you're lactose intolerant. For the second and fourth points, make sure to eat fermentable fiber. In one trial, oligofructose supplements led to sustained fat loss, without any other changes in diet (5). This is consistent with experiments in rodents showing improvements in gut bacteria profile, gut barrier health, glucose tolerance and body fat mass with oligofructose supplementation (6, 7, 8).

Oligofructose is similar to inulin, a fiber that occurs naturally in a wide variety of plants. Good sources are jerusalem artichokes, jicama, artichokes, onions, leeks, burdock and chicory root. Certain non-industrial cultures had a high intake of inulin. There are some caveats to inulin, however: inulin and oligofructose can cause gas, and can also exacerbate gastroesophageal reflux disorder (9). So don't eat a big plate of jerusalem artichokes before that important date.

The colon is packed with symbiotic bacteria, and is the site of most intestinal fermentation. The small intestine contains fewer bacteria, but gut barrier function there is critical as well. The small intestine is where the GI doctor will take a biopsy to look for celiac disease. Celiac disease is a degeneration of the small intestinal lining due to an autoimmune reaction caused by gluten (in wheat, barley and rye). This brings us to one of the most important elements of maintaining gut barrier health: avoiding food sensitivities. Gluten and casein (in dairy protein) are the two most common offenders. Gluten sensitivity is widespread and typically undiagnosed (10).

Eating raw fermented foods such as sauerkraut, kimchi, yogurt and half-sour pickles also helps maintain the integrity of the upper GI tract. I doubt these have any effect on the colon, given the huge number of bacteria already present. Other important factors in gut barrier health are keeping the ratio of omega-6 to omega-3 fats in balance, eating nutrient-dense food, and avoiding the questionable chemical additives in processed food. If triglycerides are important for leptin sensitivity, then avoiding sugar and ensuring a regular source of omega-3 should aid weight loss as well.

Strategies: Micronutrients

As I discussed in the last post, micronutrient deficiency probably plays a role in obesity, both in ways that we understand and ways that we (or I) don't. Eating a diet that has a high nutrient density and ensuring a good vitamin D status will help any sustainable fat loss strategy. The easiest way to do this is to eliminate industrially processed foods such as white flour, sugar and seed oils. These constitute more than 50% of calories for the average Westerner.

After that, you can further increase your diet's nutrient density by learning to properly prepare grains and legumes to maximize their nutritional value and digestibility (11, 12; or by avoiding grains and legumes altogether if you wish), selecting organic and/or pasture-raised foods if possible, and eating seafood including seaweed. One of the problems with extremely low-carbohydrate diets is that they may be low in water-soluble micronutrients, although this isn't necessarily the case.

Strategies: Miscellaneous

In general, exercise isn't necessarily helpful for fat loss. However, there is one type of exercise that clearly is: high-intensity intermittent training (HIIT). It's basically a fancy name for sprints. They can be done on a track, on a stationary bicycle, using weight training circuits, or any other way that allows sufficient intensity. The key is to achieve maximal exertion for several brief periods, separated by rest. This type of exercise is not about burning calories through exertion: it's about increasing hormone sensitivity using an intense, brief stressor (hormesis). Even a ridiculously short period of time spent training HIIT each week can result in significant fat loss, despite no change in diet or calorie intake (13).

Anecdotally, many people have had success using intermittent fasting (IF) for fat loss. There's some evidence in the scientific literature that IF and related approaches may be helpful (14). There are different approaches to IF, but a common and effective method is to do two complete 24-hour fasts per week. It's important to note that IF isn't about restricting calories, it's about resetting the fat mass setpoint. After a fast, allow yourself to eat quality food until you're no longer hungry.

Insufficient sleep has been strongly and repeatedly linked to obesity. Whether it's a cause or consequence of obesity I can't say for sure, but in any case it's important for health to sleep until you feel rested. If your sleep quality is poor due to psychological stress, meditating before bedtime may help. I find that meditation has a remarkable effect on my sleep quality. Due to the poor development of oral and nasal structures in industrial nations, many people do not breathe effectively and may suffer from conditions such as sleep apnea that reduce sleep quality. Overweight also contributes to these problems.

I'm sure there are other useful strategies, but that's all I have for now. If you have something to add, please put it in the comments.


* Since reducing carbohydrate intake wasn't part of the intervention, this result is observational.

The Body Fat Setpoint, Part III: Dietary Causes of Obesity

What Caused the Setpoint to Change?

We have two criteria to narrow our search for the cause of modern fat gain:

1. It has to be new to the human environment
   
2. It has to cause leptin resistance or otherwise disturb the setpoint
   

Although I believe that exercise is part of a healthy lifestyle, it probably can't explain the increase in fat mass in modern nations. I've written about that here and here. There are various other possible explanations, such as industrial pollutants, a lack of sleep and psychological stress, which may play a role. But I feel that diet is likely to be the primary cause. When you're drinking 20 oz Cokes, bisphenol-A contamination is the least of your worries.

In the last post, I described two mechanisms that may contribute to elevating the body fat set point by causing leptin resistance: inflammation in the hypothalamus, and impaired leptin transport into the brain due to elevated triglycerides. After more reading and discussing it with my mentor, I've decided that the triglyceride hypothesis is on shaky ground*. Nevertheless, it is consistent with certain observations:

• Fibrate drugs that lower triglycerides can lower fat mass in rodents and humans
  
• Low-carbohydrate diets are effective for fat loss and lower triglycerides
• Fructose can cause leptin resistance in rodents and it elevates triglycerides (1)
• Fish oil reduces triglycerides. Some but not all studies have shown that fish oil aids fat loss (2)
  

Inflammation in the hypothalamus, with accompanying resistance to leptin signaling, has been reported in a number of animal studies of diet-induced obesity. I feel it's likely to occur in humans as well, although the dietary causes are probably different for humans. The hypothalamus is the primary site where leptin acts to regulate fat mass (3). Importantly, preventing inflammation in the brain prevents leptin resistance and obesity in diet-induced obese mice (3.1). The hypothalamus is likely to be the most important site of action. Research is underway on this.

The Role of Digestive Health

What causes inflammation in the hypothalamus? One of the most interesting hypotheses is that increased intestinal permeability allows inflammatory substances to cross into the circulation from the gut, irritating a number of tissues including the hypothalamus.

Dr. Remy Burcelin and his group have spearheaded this research. They've shown that high-fat diets cause obesity in mice, and that they also increase the level of an inflammatory substance called lipopolysaccharide (LPS) in the blood. LPS is produced by gram-negative bacteria in the gut and is one of the main factors that activates the immune system during an infection. Antibiotics that kill gram-negative bacteria in the gut prevent the negative consequences of high-fat feeding in mice.

Burcelin's group showed that infusing LPS into mice on a low-fat chow diet causes them to become obese and insulin resistant just like high-fat fed mice (4). Furthermore, adding 10% of the soluble fiber oligofructose to the high-fat diet prevented the increase in intestinal permeability and also largely prevented the body fat gain and insulin resistance from high-fat feeding (5). Oligofructose is food for friendly gut bacteria and ends up being converted to butyrate and other short-chain fatty acids in the colon. This results in lower intestinal permeability to toxins such as LPS. This is particularly interesting because oligofructose supplements cause fat loss in humans (6).

A recent study showed that blood LPS levels are correlated with body fat, elevated cholesterol and triglycerides, and insulin resistance in humans (7). However, a separate study didn't come to the same conclusion (8). The discrepancy may be due to the fact that LPS isn't the only inflammatory substance to cross the gut lining-- other substances may also be involved. Anything in the blood that shouldn't be there is potentially inflammatory.

Overall, I think gut dysfunction probably plays a major role in obesity and other modern metabolic problems. Insufficient dietary fiber, micronutrient deficiencies, excessive gut irritating substances such as gluten, abnormal bacterial growth due to refined carbohydrates (particularly sugar), and omega-6:3 imbalance may all contribute to abnormal gut bacteria and increased gut permeability.

The Role of Fatty Acids and Micronutrients

Any time a disease involves inflammation, the first thing that comes to my mind is the balance between omega-6 and omega-3 fats. The modern Western diet is heavily weighted toward omega-6, which are the precursors to some very inflammatory substances (as well as a few that are anti-inflammatory). These substances are essential for health in the correct amounts, but they need to be balanced with omega-3 to prevent excessive and uncontrolled inflammatory responses. Animal models have repeatedly shown that omega-3 deficiency contributes to the fat gain and insulin resistance they develop when fed high-fat diets (9, 10, 11).

As a matter of fact, most of the papers claiming "saturated fat causes this or that in rodents" are actually studying omega-3 deficiency. The "saturated fats" that are typically used in high-fat rodent diets are refined fats from conventionally raised animals, which are very low in omega-3. If you add a bit of omega-3 to these diets, suddenly they don't cause the same metabolic problems, and are generally superior to refined seed oils, even in rodents (12, 13).

I believe that micronutrient deficiency also plays a role. Inadequate vitamin and mineral status can contribute to inflammation and weight gain. Obese people typically show deficiencies in several vitamins and minerals. The problem is that we don't know whether the deficiencies caused the obesity or vice versa. Refined carbohydrates and refined oils are the worst offenders because they're almost completely devoid of micronutrients.

Vitamin D in particular plays an important role in immune responses (including inflammation), and also appears to influence body fat mass. Vitamin D status is associated with body fat and insulin sensitivity in humans (14, 15, 16). More convincingly, genetic differences in the vitamin D receptor gene are also associated with body fat mass (17, 18), and vitamin D intake predicts future fat gain (19).

Exiting the Niche

I believe that we have strayed too far from our species' ecological niche, and our health is suffering. One manifestation of that is body fat gain. Many factors probably contribute, but I believe that diet is the most important. A diet heavy in nutrient-poor refined carbohydrates and industrial omega-6 oils, high in gut irritating substances such as gluten and sugar, and a lack of direct sunlight, have caused us to lose the robust digestion and good micronutrient status that characterized our distant ancestors. I believe that one consequence has been the dysregulation of the system that maintains the fat mass "setpoint". This has resulted in an increase in body fat in 20th century affluent nations, and other cultures eating our industrial food products.

In the next post, I'll discuss my thoughts on how to reset the body fat setpoint.


* The ratio of leptin in the serum to leptin in the brain is diminished in obesity, but given that serum leptin is very high in the obese, the absolute level of leptin in the brain is typically not lower than a lean person. Leptin is transported into the brain by a transport mechanism that saturates when serum leptin is not that much higher than the normal level for a lean person. Therefore, the fact that the ratio of serum to brain leptin is higher in the obese does not necessarily reflect a defect in transport, but rather the fact that the mechanism that transports leptin is already at full capacity.

The Body Fat Setpoint, Part II: Mechanisms of Fat Gain

The Timeline of Fat Gain

Modern humans are unusual mammals in that fat mass varies greatly between individuals. Some animals carry a large amount of fat for a specific purpose, such as hibernation or migration. But all individuals of the same sex and social position will carry approximately the same amount of fat at any given time of year. Likewise, in hunter-gatherer societies worldwide, there isn't much variation in body weight-- nearly everyone is lean. Not necessarily lean like Usain Bolt, but not overweight.

Although overweight and obesity occurred forty years ago in the U.S. and U.K., they were much less common than today, particularly in children. Here are data from the U.S. Centers for Disease Control NHANES surveys (from this post):

Together, this shows that a) leanness is the most natural condition for the human body, and b) something about our changing environment, not our genes, has caused our body fat to grow.

Fat Mass is Regulated by a Feedback Circuit Between Fat Tissue and the Brain

In the last post, I described how the body regulates fat mass, attempting to keep it within a narrow window or "setpoint". Body fat produces a hormone called leptin, which signals to the brain and other organs to decrease appetite, increase the metabolic rate and increase physical activity. More fat means more leptin, which then causes the extra fat to be burned. The little glitch is that some people become resistant to leptin, so that their brain doesn't hear the fat tissue screaming that it's already full. Leptin resistance nearly always accompanies obesity, because it's a precondition of significant fat gain. If a person weren't leptin resistant, he wouldn't have the ability to gain more than a few pounds of fat without heroic overeating (which is very very unpleasant when your brain is telling you to stop). Animal models of leptin resistance develop something that resembles human metabolic syndrome (abdominal obesity, blood lipid abnormalities, insulin resistance, high blood pressure).

The Role of the Hypothalamus

The hypothalamus is on the underside of the brain connected to the pituitary gland. It's the main site of leptin action in the brain, and it controls the majority of leptin's effects on appetite, energy expenditure and insulin sensitivity. Most of the known gene variations that are associated with overweight in humans influence the function of the hypothalamus in some way (1). Not surprisingly, leptin resistance in the hypothalamus has been proposed as a cause of obesity. It's been shown in rats and mice that hypothalamic leptin resistance occurs in diet-induced obesity, and it's almost certainly the case in humans as well. What's causing leptin resistance in the hypothalamus?

There are three leading explanations at this point that are not mutually exclusive. One is cellular stress in the endoplasmic reticulum, a structure inside the cell that's used for protein synthesis and folding. I've read the most recent paper on this in detail, and I found it unconvincing (2). I'm open to the idea, but it needs more rigorous support.

A second explanation is inflammation in the hypothalamus. Inflammation inhibits leptin and insulin signaling in a variety of cell types. At least two studies have shown that diet-induced obesity in rodents leads to inflammation in the hypothalamus (3, 4)*. If leptin is getting to the hypothalamus, but the hypothalamus is insensitive to it, it will require more leptin to get the same signal, and fat mass will creep up until it reaches a higher setpoint.

The other possibility is that leptin simply isn't reaching the hypothalamus. The brain is a unique organ. It's enclosed by the blood-brain barrier (BBB), which greatly restricts what can enter and leave it. Both insulin and leptin are actively transported across the BBB. It's been known for a decade that obesity in rodents is associated with a lower rate of leptin transport across the BBB (5, 6).

What causes a decrease in leptin transport across the BBB? Triglycerides are a major factor. These are circulating fats going from the liver and the digestive tract to other tissues. They're one of the blood lipid measurements the doctor makes when he draws your blood. Several studies in rodents have shown that high triglycerides cause a reduction in leptin transport across the BBB, and reducing triglycerides allows greater leptin transport and fat loss (7, 8). In support of this theory, the triglyceride-reducing drug gemfibrozil also causes weight loss in humans (9)**. Guess what else reduces triglycerides and causes weight loss? Low-carbohydrate diets, and avoiding sugar and refined carbohydrates in particular.

In the next post, I'll get more specific about what factors could be causing hypothalamic inflammation and/or reduced leptin transport across the BBB. I'll also discuss some ideas on how to reduce leptin resistance sustainably through diet and exercise.


* This is accomplished by feeding them sad little pellets that look like greasy chalk. They're made up mostly of lard, soybean oil, casein, maltodextrin or cornstarch, sugar, vitamins and minerals (this is a link to the the most commonly used diet for inducing obesity in rodents). Food doesn't get any more refined than this stuff, and adding just about anything to it, from fiber to fruit extracts, makes it less damaging.

** Fibrates are PPAR agonists, so the weight loss could also be due to something besides the reduction in triglycerides.

New Saturated Fat Review Article by Dr. Ronald Krauss

I never thought I'd see the day when one of the most prominent lipid researchers in the world did an honest review of the observational studies evaluating the link between saturated fat and cardiovascular disease. Dr. Ronald Krauss's group has published a review article titled "Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease". As anyone with two eyes and access to the medical literature would conclude (including myself), they found no association whatsoever between saturated fat intake and heart disease or stroke:

A meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD.

Bravo, Dr. Krauss. That was a brave move.

Thanks to Peter for pointing out this article.