Healthy Skeptic Podcast

Chris Kresser has just posted our recent interview/discussion on his blog The Healthy Skeptic.  You can listen to it on Chris's blog here.  The discussion mostly centered around body fat and food reward.  I also answered a few reader questions.  Here are some highlights:

• How does the food reward system work? Why did it evolve?
• Why do certain flavors we don’t initially like become appealing over time?
• How does industrially processed food affect the food reward system?
• What’s the most effective diet used to make rats obese in a research setting? What does this tell us about human diet and weight regulation?
• Do we know why highly rewarding food increases the set point in some people but not in others?
• How does the food reward theory explain the effectiveness of popular fat loss diets?
• Does the food reward theory tell us anything about why traditional cultures are generally lean?
• What does cooking temperature have to do with health?
• Reader question: How does one lose fat?
• Reader question: What do I (Stephan) eat?
• Reader question: Why do many people gain fat with age, especially postmenopausal women?

The podcast is a sneak preview of some of the things I'll be discussing in the near future.  Enjoy!

Food Reward: a Dominant Factor in Obesity, Part III

Low-Fat Diets

In 2000, the International Journal of Obesity published a nice review article of low-fat diet trials.  It included data from 16 controlled trials lasting from 2-12 months and enrolling 1,910 participants (1).  What sets this review apart is it only covered studies that did not include instructions to restrict calorie intake (ad libitum diets).  On average, low-fat dieters reduced their fat intake from 37.7 to 27.5 percent of calories.  Here's what they found:
Read more »

Clarifications About Carbohydrate and Insulin

My statements about carbohydrate and insulin in the previous post seem to have kicked up some dust!  Some people are even suggesting I've gone low-fat!  I'm going to take this opportunity to be more specific about my positions.

I do not think that post-meal insulin spikes contribute to obesity, and they may even oppose it.  I'm not aware of anyone who researches metabolism for a living who thinks post-meal insulin spikes contribute to obesity, and after having looked into it, I understand why.  It's not a controversial issue in my field as far as I can tell. Elevated fasting insulin is a separate issue-- that's a marker of insulin resistance.  It's important not to confuse the two.  Does insulin resistance contribute to obesity?  I don't know, but it's hypothetically possible since insulin acts like leptin's kid brother in some ways.  As far as I can tell, starch per se and post-meal insulin spikes do not lead to insulin resistance.
Read more »

Healthy Skeptic Podcast and Reader Questions

Chris Kresser, Danny Roddy and I just finished recording the podcast that will be released on May 24th.  It went really well, and we think you'll find it informative and maybe even practical!

Unfortunately, we only got around to answering three of the questions I had selected:

1. How does one lose fat?
2. What do I (Stephan) eat?
3. Why do many people gain fat with age, especially postmenopausal women?

I feel guilty about that, so I'm going to answer three more right now.

Read more »

Interview with Chris Voigt of 20 Potatoes a Day

Introduction

Chris Voigt is the executive director of the Washington State Potato Commission, which supports and promotes the Washington state potato industry (1). On October 1st, Mr. Voigt began a two month, potato-only diet to raise awareness about the health properties of potatoes. It was partially in response to the recent decision by the federal WIC (Women, Infants and Children) low-income assistance program to remove potatoes from the list of vegetables it will pay for. Mr. Voigt's potato diet has been a media sensation, leading to widespread coverage in several countries. He maintains a website and blog called 20 Potatoes a Day.


Diet Facts

For 60 days, Mr Voigt's diet consisted of nothing but potatoes and a small amount of cooking oil (canola and olive), with no added nutritional supplements. Based on what he has told me, I estimate that 10-15% of his calories came from fat, 10% from protein and 75-80% from high-glycemic carbohydrate. His calorie intake ranged from 1,600 kcal (first 3 weeks) to 2,200 kcal (remaining 5.5 weeks) per day. Prior to the diet, he estimated that his calorie requirement was 2,200 kcal, so he attempted to stay as close to that as possible.

Health Markers

Mr. Voigt has posted the results of physical examinations, including bloodwork, from the beginning, middle and end of the diet. The change he experienced during that time is nothing short of remarkable. He shed 21 pounds, his fasting glucose decreased by 10 mg/dL (104 to 94 mg/dL), his serum triglycerides dropped by nearly 50%, his HDL cholesterol increased slightly, and his calculated LDL cholesterol dropped by a stunning 41% (142 to 84 mg/dL). The changes in his HDL, triglycerides and fasting glucose are consistent with improved insulin sensitivity (2, 3), and are not consistent with a shift of LDL particle size to the dangerous "small, dense" variety (4).

Interview

What was your diet like prior to the potato diet?

My best estimate is that it was probably a little better than the average US citizen only because of a high rate of produce consumption. I generally would eat about 10 servings of fruits and vegetables a day. But I ate everything else too. I would eat a wide range of food, a little bit of everything, including foods that aren’t considered “healthy”.

You essentially ate nothing but potatoes, fat and flavorings for two months. Can you give us an idea of how much fat you were eating? What kind of fat was it?

I averaged about 2 tablespoons of cooking oil a day over the span of the 60 days. Canola oil was used for frying and olive oil was used for roasting.

How was your digestion?

Potatoes are pretty easy on the digestive system. I actually got a lot of emails from people who suffer from severe digestive disorders and literally, potatoes are the only thing they can eat. My 60 days of potatoes was nothing compared to some folks with these digestive disorders. I was getting a lot of fiber so things were pretty regular, but not too regular :)

You lost 21 pounds during your two months of eating only potatoes. Do you have a sense of whether it came out of fat, muscle or both? For example, did your pants become looser?

Pants definitely became looser. I also noticed it in my neck size for shirts. I’m assuming most all of it was due to fat loss.

Do you think you were able to meet your calorie goal of 2,200 calories per day? Were you hungry during the diet?

I was not meeting the goal of 2,200 calories a day during the first 3 weeks of the diet. During the first three weeks of the diet I only ate until I was full. I didn’t realize that potatoes would give me such a high sense of fullness after each meal. So for those first 3 weeks, I was only consuming about 1,600 calories a day. After the third week I had lost 12 pounds and realized that I needed to change strategy. I then began to eat more potatoes despite the sense of fullness I was experiencing. So for the remaining 5 ½ weeks I was very diligent about eating the 2,200 calories. I continued to lose weight but at a slower place. I lost an additional 9 pounds over the course of those remaining 5 1/2 weeks. At the start of my diet I estimated, via a couple different on line calorie calculators, that I burn about 2,200 calories a day. Since I continued to lose weight, I’m assuming I actually burn closer to 2,800 calories a day. Something that may have also played a role in continued weight loss was the amount of resistant starch I was getting from potatoes. I ate a lot of cooked potatoes that had been refrigerated. These are generally higher in resistant starch. If I were to do the diet again, I would like to set up an experiment to gauge the effect of resistant starch.

What foods did you crave the most?

I craved mostly foods that had a “juicy crunch”, like an apple, or cucumbers, or carrots, or celery. I never acquired a taste for raw potatoes so virtually all the potatoes I consumed were cooked. No matter how you cook your potatoes, you always get that same soft cooked texture. I craved foods with a crisper texture.

How was your energy level?

My energy level was very good the entire time of the diet. I really didn’t notice a change in energy at the start of the diet so I assumed that the potato diet didn’t have a positive or negative effect on my energy level. It wasn’t until I finished the diet and started to consume other foods that I noticed my energy level has seemed to drop a bit.

How did you feel overall? Were there any unexpected effects of the diet?

I felt really good on the diet. I had lots of energy, slept good at night, and seemed to avoid the cold viruses that circulated at home and work.

The only unusual thing that occurred is what my wife told me. I’m a habitual snorer. The day I started eating only potatoes, my snoring stopped. It restarted the day I started to include other foods in my diet. I’m assuming it was just some weird coincidence but that’s what she tells me.

My doctor and I expected my cholesterol to drop but not at the level we saw. I’ve had borderline high cholesterol for the past decade. I started the diet at 214 and saw it drop to 147 at the end of 60 days. We anticipated a drop of maybe 10-25 points. It was a huge surprise to see a 67 point drop.

Your fasting glucose went from 104 mg/dL, which I consider high, to 94 mg/dL, which is on the high side for someone eating a high-carbohydrate diet, but within the clinically normal range. Do you have a family history of diabetes?

No history of diabetes. My parents are in their early eighties and their parents lived to their 70’s and 80’s with no history of type one or two diabetes.

Reading your blog posts, it seemed like you were having a hard time with the diet at first, but after a while you complained less and even seemed to enjoy it at times. Did you get used to it?

I would say that week 2 and 3 were probably the hardest. The first week was easy probably because of the novelty of the diet. Then reality set in for week 2 and 3. After that, I found my groove and it got easier. During the work week was easy but weekends, particularly Sunday’s, were the hardest. During the work week I did most of my eating at my desk so I wasn’t around a lot of other people eating or surrounded by other foods. Weekends were more difficult because I was around other people every meal and always had other foods in front of me at home.

What kinds of potatoes did you eat?

I literally ate every kind of potato I could get my hands on. I ate yellow skin/yellow flesh potatoes, red skin/white flesh, red skin/red flesh, purple skin/white flesh, purple skin/purple flesh, russet potatoes with white flesh, russet potatoes with yellow flesh, white potatoes, yellow potatoes with white flesh, purple fingerlings, yellow fingerlings, red fingerlings and numerous experimental varieties.

Did you peel them or eat the skin?

I ate the skin at least 90% of the time if not more. There is a myth that all the nutrition in a potato is in the skin or right under the skin. That’s not true, there are nutrients spread throughout the potato but most of the fiber is located in the skin.

What variety of potato is your favorite?

It really depended on the cooking method. For frying, I preferred russet potatoes. For baking, I preferred red potatoes. For mashed, I preferred yellow potatoes. For roasting, a toss-up between russets and reds.

How long did it take you after the diet ended to eat another potato?

As strange as it sounds, potatoes were my first two meals after my diet ended. I was saving my first non-potato meal for a special event that was planned at the local Head Start facility. The beef, dairy, apple, and potato producers put together a nice dinner event and nutrition workshop for all the kids and their parents at the Head Start center in Moses Lake. I still eat potatoes pretty regularly, but most of the time now I’m eating them with more than just seasonings.

Are there any other facts about potatoes you think Whole Health Source readers might find interesting?

Just a reminder that I’m not encouraging anyone to follow in my footsteps and eat just potatoes. This diet is not intended to be the next “fad” diet but was simply a bold statement to remind people that there is a tremendous amount of nutrition in a potato. There is no one food product that can meet all of your nutritional needs. I fully support a well balanced healthy diet, which potatoes can be a part of.

In 2008, the United Nations declared it to be the “Year of the Potato”. This was done to bring attention to the fact that the potato is one of the most efficient crops for developing nations to grow, as a way of delivery a high level of nutrition to growing populations, with fewer needed resources than other traditional crops. In the summer of 2010, China approved new government policies that positioned the potato as the key crop to feed its growing population. The Chinese government formed a partnership with the International Potato Center in Peru to help them facilitate this new emphasis on the potato.

Thanks Chris, for doing your experiment and taking the time to share these details with us!

In the next post, I'll give my interpretation of all this.

Dr. Mellanby's Tooth Decay Reversal Diet

I have a lot of admiration for Drs. Edward and May Mellanby. A husband-and-wife team, they discovered vitamin D, and determined that rickets is caused by poor calcium (or phosphorus) status, typically due to vitamin D deficiency. They believed that an ideal diet is omnivorous, based on whole foods, and offers an adequate supply of fat-soluble vitamins and easily absorbed minerals. They also felt that grain intake should be modest, as their research showed that unsoaked whole grains antagonize the effect of vitamins D and A.

Not only did the Mellanbys discover vitamin D and end the rickets epidemic that was devastating Western cities at the time, they also discovered a cure for early-stage tooth decay that has been gathering dust in medical libraries throughout the world since 1924.

It was in that year that Dr. May Mellanby published a summary of the results of the Mellanby tooth decay reversal studies in the British Medical Journal, titled "Remarks on the Influence of a Cereal-free Diet Rich in Vitamin D and Calcium on Dental Caries in Children". Last year, I had to specially request this article from the basement of the University of Washington medical library (1). Thanks to the magic of the internet, the full version of the paper is now freely available online (2).

You don't need my help to read the study, but in this post I offer a little background, a summary and my interpretation.

In previous studies, the Mellanbys used dogs to define the dietary factors that influence tooth development and repair. They identified three, which together made the difference between excellent and poor dental health (from Nutrition and Disease):

1. The diet's mineral content, particularly calcium and phosphorus
2. The diet's fat-soluble vitamin content, chiefly vitamin D
3. The diet's content of inhibitors of mineral absorption, primarily phytic acid

Once they had defined these factors, they set about testing their hypotheses in humans. They performed eight trials, each one in children in an institutionalized setting where diet could be completely controlled. The number of cavities in each child's mouth was noted at the beginning and end of the period. I'll only discuss the three most informative, and only the most successful in detail. First, the results:

I'll start with diet 1. Children on this diet ate the typical fare, plus extra oatmeal. Oatmeal is typically eaten as an unsoaked whole grain (and soaking it isn't very effective in any case), and so it is high in phytic acid, which effectively inhibits the absorption of a number of minerals including calcium. These children formed 5.8 cavities each and healed virtually none-- not good!

Diet number 2 was similar to diet 1, except there was no extra oatmeal and the children received a large supplemental dose of vitamin D. Over 28 weeks, only 1 cavity per child developed or worsened, while 3.9 healed. Thus, simply adding vitamin D to a reasonable diet allowed most of their cavities to heal.

Diet number 3 was the most effective. This was a grain-free diet plus supplemental vitamin D. Over 26 weeks, children in this group saw an average of only 0.4 cavities form or worsen, while 4.7 healed. The Mellanbys considered that they had essentially found a cure for this disorder in its early stages.

What exactly was this diet? Here's how it was described in the paper (note: cereals = grains):

...instead of cereals- for example, bread, oatmeal, rice, and tapioca- an increased allowance of potatoes and other vegetables, milk, fat, meat, and eggs was given. The total sugar, jam, and syrup intake was the same as before. Vitamin D was present in abundance in either cod-liver oil or irradiated ergosterol, and in egg yolk, butter, milk, etc. The diet of these children was thus rich in those factors, especially vitamin D and calcium, which experimental evidence has shown to assist calcification, and was devoid of those factors- namely, cereals- which interfere with the process.

Carbohydrate intake was reduced by almost half. Bread and oatmeal were replaced by potatoes, milk, meat, fish, eggs, butter and vegetables. The diet is reminiscent of what Dr. Weston Price used to reverse tooth decay in his dental clinic in Cleveland, although Price's diet did include rolls made from freshly ground whole wheat. Price also identified the fat-soluble vitamin K2 MK-4 as another important factor in tooth decay reversal, which would have been abundant in Mellanby's studies due to the dairy. The Mellanbys and Price were contemporaries and had parallel and complementary findings. The Mellanbys did not understand the role of vitamin K2 in mineral metabolism, and Price did not seem to appreciate the role of phytic acid from unsoaked whole grains in preventing mineral absorption.

Here are two sample meals provided in Dr. Mellanby's paper. I believe the word "dinner" refers to the noon meal, and "supper" refers to the evening meal:

Breakfast- Omelette, cocoa, with milk.
Lunch- Milk.
Dinner- Potatoes, steamed minced meat, carrots, stewed fruit, milk.
Tea- Fresh fruit salad, cocoa made with milk.
Supper- Fish and potatoes fried in dripping, milk.

Breakfast- Scrambled egg, milk, fresh salad.
Dinner- Irish stew, potatoes, cabbage, stewed fruit, milk.
Tea- Minced meat warmed with bovril, green salad, milk.
Supper- Thick potato soup made with milk.

In addition, children received vitamin D daily. Here's Dr. Mellanby's summary of their findings:

The tests do not indicate that in order to prevent dental caries children must live on a cereal-free diet, but in association with the results of the other investigations on animals and children they do indicate that the amount of cereal eaten should be reduced, particularly during infancy and in the earlier years of life, and should be replaced by an increased consumption of milk, eggs, butter, potatoes, and other vegetables. They also indicate that a sufficiency of vitamin D and calcium should be given from birth, and before birth, by supplying a suitable diet to the pregnant mother. The teeth of the children would be well formed and more resistant to dental caries instead of being hypoplastic and badly calcified, as were those in this investigation.

If I could add something to this program, I would recommend daily tooth brushing and flossing, avoiding sugar, and rinsing the mouth with water after each meal.

This diet is capable of reversing early stage tooth decay. It will not reverse advanced decay, which requires professional dental treatment as soon as possible. It is not a substitute for dental care in general, and if you try using diet to reverse your own tooth decay, please do it under the supervision of a dentist. And while you're there, tell her about Edward and May Mellanby!

Preventing Tooth Decay
Reversing Tooth Decay
Images of Tooth Decay Healing due to an Improved Diet
Dental Anecdotes

Glucose Tolerance in Non-industrial Cultures

Background

Glucose is the predominant blood sugar and one of the body's two main fuel sources (the other is fatty acids). Glucose, in one form or another, is also the main form of digestible dietary carbohydrate in nearly all human diets. Starch is made of long chains of glucose molecules, which are rapidly liberated and absorbed during digestion. Sucrose, or table sugar, is made of one glucose and one fructose molecule, which are separated before absorption.

Blood glucose is essential for life, but it can also be damaging if there is too much of it. Therefore, the body tries to keep it within a relatively tight range. Normal fasting glucose is roughly between 70 and 90 mg/dL*, but in the same individual it's usually within about 5 mg/dL on any given day. Sustained glucose above 160 mg/dL or so causes damage to multiple organ systems. Some people would put that number closer to 140 mg/dL.

The amount of glucose contained in a potato far exceeds the amount contained in the blood, so if all that glucose were to enter the blood at once, it would lead to a highly damaging blood glucose level. Fortunately, the body has a hormone designed to keep this from happening: insulin. Insulin tells cells to internalize glucose from the blood. It's released by the pancreas in response to eating carbohydrate, and protein to a lesser extent. The amount of insulin released is proportional to the amount of carbohydrate ingested, so that glucose entering the blood is cleared before it can accumulate.

Insulin doesn't clear all the glucose as it enters the bloodstream, however. Some of it does accumulate, leading to a spike in blood glucose. This usually doesn't exceed 160 mg/dL in a healthy person, and even if it approaches that level it's only briefly. However, diabetics have reduced insulin signaling, and eating a typical meal can cause their glucose to exceed 300 mg/dL due to reduced clearance. In affluent nations, this is typically due to type II diabetes, which begins as insulin resistance, a condition in which insulin is actually higher than normal but cells fail to respond to it.

The precursor to diabetes is called glucose intolerance, or pre-diabetes. In someone with glucose intolerance, blood glucose after a typical meal will exceed that of a healthy person, but will not reach the diabetic range (a common definition of diabetes is 200 mg/dL or higher, 2 hours after ingesting 75g of glucose). Glucose tolerance refers to a person's ability to control blood glucose when challenged with dietary glucose, and can be used in some contexts as a useful predictor of diabetes risk and general metabolic health. Doctors use the oral glucose tolerance test (OGTT), which involves drinking 60-100g glucose and measuring blood glucose after one or two hours, to determine glucose tolerance.

Why do we care about glucose tolerance in non-industrial cultures?

One of the problems with modern medical research is that so many people in our culture are metabolically sick that it can be difficult to know if what we consider "normal" is really normal or healthy in the broader sense. Non-industrial cultures allow us to examine what the human metabolism is like in the absence of metabolic disease. I admit this rests on certain assumptions, particularly that these people aren't sick themselves. I don't think all non-industrial cultures are necessarily healthy, but I'm going to stick with those that research has shown have an exceptionally low prevalence of diabetes (by Western standards) and other "diseases of civilization" for the purposes of this post.

Here's the question I really want to answer in this post: do healthy non-industrial cultures with a very high carbohydrate intake have an excellent glucose tolerance, such that their blood glucose doesn't rise to a high level, or are they simply resistant to the damaging effects of high blood glucose?

The data

I'm going to start with an extreme example. In the 1960s, when it was fashionable to study non-industrial cultures, researchers investigated the diet and health of a culture in Tukisenta, in the highlands of Papua New Guinea. The eat practically nothing but sweet potatoes, and their typical daily fare is 94.6 percent carbohydrate. Whether or not you believe that exact number, their diet was clearly extraordinarily high in carbohydrate. They administered 100g OGTTs and measured blood glucose at one hour, which is a very stringent OGTT. They compared the results to those obtained in the 1965 Tecumseh study (US) obtained by the same method. Here's what they found (1):
Compared to Americans, in Tukisenta they had an extraordinary glucose tolerance at all ages. At one hour, their blood glucose was scarcely above normal fasting values, and glucose tolerance only decreased modestly with age. In contrast, in Americans over 50 years old, the average one-hour value was approaching the diabetic range!

Now let's take a look at the African Bantu in the Lobaye region of the Central African Republic. The Bantu are a large ethnic group who primarily subsist on a diverse array of starchy foods including grains, beans, plantains and root crops. One hour after a 100g OGTT, their blood glucose was 113 mg/dL, compared to 139 mg/dL in American controls (2). Those numbers are comparable to what investigators found in Tukisenta, and indicate an excellent glucose tolerance in the Bantu.

In South America, different investigators studied a group of native Americans in central Brazil that subsist primarily on cassava (a starchy root crop) and freshwater fish. Average blood glucose one hour after a 100g OGTT was 94 mg/dl, and only 2 out of 106 people tested had a reading over 160 mg/dL (both were older women) (Western Diseases: Their Emergence and Prevention, p. 149). Again, that indicates a phenomenal glucose tolerance by Western standards.

I have to conclude that high-carbohydrate non-industrial cultures probably don't experience damaging high blood glucose levels, because their glucose tolerance is up to the task of shuttling a huge amount of glucose out of the bloodstream before that happens.

Not so fast...

Now let's turn our attention to another study that may throw a wrench in the gears. A while back, I found a paper containing OGTT data for the !Kung San (also called the Bushmen), a hunter-gatherer group living in the Kalahari desert of Africa. I reported in an earlier post that they had a good glucose tolerance. When I revisited the paper recently, I realized I had misread it and in fact, their glucose tolerance was actually pretty poor (come on guys, you have to call me on this stuff!).

Investigators administered a 50g OGTT, half what the other studies used. At one hour, the San had blood glucose readings of 169 mg/dL, compared to 142 mg/dL in Caucasian controls (3)! I suspect a 100g OGTT would have put them close to the diabetic range.

Wait a minute, these guys are hunter-gatherers living the ancestral lifestyle; aren't they supposed to be super healthy?? While I was mulling this over, I recalled a discussion on Peter's blog hyperlipid where commenters were discussing their diabetic OGTT values while on a low-carbohydrate diet. Apparently, carbohydrate refeeding for a few days generally reverses this and allows a normal OGTT in most people. It turns out this effect has been known for the better part of a century.

So what were the San eating? The study was conducted in October of 1970. The San diet changes seasonally, however their main staple food is the mongongo nut, which is mostly fat and which is available year-round (according to The !Kung San: Men, Women and Work in a Foraging Society). Their carbohydrate intake is generally low by Western standards, and at times of the year it is very low. This varies by the availability of other foods, but they generally don't seem to relish the fibrous starchy root crops that are available in the area, as they mostly eat them when other food is scarce. Jean-Louis Tu has posted a nice analysis of the San diet on BeyondVeg (4). Here's a photo of a San man collecting mongongo nuts from The !Kung San: Men, Women and Work in a Foraging Society:

What did the authors of the OGTT study have to say about their diet? Acknowledging that prior carbohydrate intake may have played a role in the OGTT results of the San, they made the following remark:

a retrospective dietary history (M. J. Konner, personal communication, 1971) indicated that the [San], in fact, consumed fairly large amounts of carbohydrate-rich vegetable food during the week before testing.

However, the dietary history was not provided, nor has it been published, so we have no way to assess the statement's accuracy or what was meant by "fairly large amounts of carbohydrate-rich vegetable food." Given the fact that the San diet generally ranges from moderately low to very low in carbohydrate, I suspect they were not getting much carbohydrate as a percentage of calories. Looking at the nutritional value of the starchy root foods they typically ate in appendix D of The !Kung San: Men, Women and Work in a Foraging Society, they are fibrous and most contain a low concentration of starch compared to a potato for example. The investigators may have been misled by the volume of these foods eaten, not realizing that they are not as rich in carbohydrate as the starchy root crops they are more familiar with.

You can draw your own conclusions, but I think the high OGTT result of the San probably reflect a low habitual carbohydrate intake, and not pre-diabetes. I have a very hard time believing that this culture wasn't able to handle the moderate amount of carbohydrate in their diet effectively, as observers have never described diabetic complications among them.

Putting it all together

This brings me to my hypothesis. I think a healthy human body is extraordinarily flexible in its ability to adapt to a very broad range of carbohydrate intakes, and adjusts glucose tolerance accordingly to maintain carbohydrate handling in a healthy range. In the context of a healthy diet and lifestyle (from birth), I suspect that nearly anyone can adjust to a very high carbohydrate intake without getting dangerous blood glucose spikes. A low carbohydrate intake leads to lower glucose handling and better fat handling, as one would expect. This can show up as impaired glucose tolerance or diabetes on an OGTT, but that does not necessarily reflect a pathological state in my opinion.

Every person is different based on lifestyle, diet, personal history and genetics. Not everyone in affluent nations has a good glucose tolerance, and some people will never be able to handle starch effectively under any circumstances. The best way to know how your body reacts to carbohydrate is to test your own post-meal blood glucose using a glucose meter. They are inexpensive and work well. For the most informative result, eat a relatively consistent amount of carbohydrate for a week to allow your body to adapt, then take a glucose measurement 1 and 2 hours after a meal. If you don't eat much carbohydrate, eating a potato might make you think you're diabetic, whereas after a week of adaptation you may find that a large potato does not spike your blood glucose beyond the healthy range.

Exercise is a powerful tool for combating glucose intolerance, as it increases the muscles' demand for glucose, causing them to transport it out of the blood greedily after a meal. Any exercise that depletes muscle glycogen should be effective.


* Assuming a typical carbohydrate intake. Chris Kresser recently argued, based on several studies, that true normal fasting glucose for a person eating a typical amount of carbohydrate is below 83 mg/dL. Low-carbohydrate eating may raise this number, but that doesn't necessarily indicate a pathological change. High-carbohydrate cultures such as the Kitavans, Aymara and New Guineans tend to have fasting values in the low 60s to low 70s. I suspect that a very high carbohydrate intake generally lowers fasting glucose in healthy people. That seems to be the case so far for Chris Voigt, on his diet of 20 potatoes a day. Stay tuned for an interview with Mr. Voigt in early December.

Interview with Jimmy Moore

About two months ago, I did an interview with Jimmy Moore of the Livin' la Vida Low Carb internet empire. I hardly remember what we talked about, but I think it went well. I enjoyed Jimmy's pleasant and open-minded attitude. Head over to Jimmy's website and listen to the interview here.

I do recall making at least one mistake. When discussing heart attacks,I said "atrial fibrillation" when I meant "ventricular fibrillation".

The Inuit: Lessons from the Arctic

The Inuit (also called Eskimo) are a group of hunter-gatherer cultures who inhabit the arctic regions of Alaska, Canada and Greenland. They are a true testament to the toughness, adaptability and ingenuity of the human species. Their unique lifestyle has a lot of information to offer us about the boundaries of the human ecological niche. Weston Price was fascinated by their excellent teeth, good nature and overall robust health. Here's an excerpt from Nutrition and Physical Degeneration:

"In his primitive state he has provided an example of physical excellence and dental perfection such as has seldom been excelled by any race in the past or present...we are also deeply concerned to know the formula of his nutrition in order that we may learn from it the secrets that will not only aid in the unfortunate modern or so-called civilized races, but will also, if possible, provide means for assisting in their preservation."

The Inuit are cold-hardy hunters whose traditional diet consists of a variety of sea mammals, fish, land mammals and birds. They invented some very sophisticated tools, including the kayak, whose basic design has remained essentially unchanged to this day. Most groups ate virtually no plant food. Their calories came primarily from fat, up to 75%, with almost no calories coming from carbohydrate. Children were breast-fed for about three years, and had solid food in their diet almost from birth. As with most hunter-gatherer groups, they were free from chronic disease while living a traditional lifestyle, even in old age. Here's a quote from Observations on the Western Eskimo and the Country they Inhabit; from Notes taken During two Years [1852-54] at Point Barrow, by Dr. John Simpson:

These people [the Inuit] are robust, muscular and active, inclining rather to spareness [leanness] than corpulence [overweight], presenting a markedly healthy appearance. The expression of the countenance is one of habitual good humor. The physical constitution of both sexes is strong. Extreme longevity is probably not unknown among them; but as they take no heed to number the years as they pass they can form no guess of their own ages.

One of the common counterpoints I hear to the idea that high-fat hunter-gatherer diets are healthy, is that exercise protects them from the ravages of fat. The Inuit can help us get to the bottom of this debate. Here's a quote from Cancer, Disease of Civilization (1960, Vilhjalmur Stefansson):

"They are large eaters, some of them, especially the women, eating all the time..." ...during the winter the Barrow women stirred around very little, did little heavy work, and yet "inclined more to be sparse than corpulent" [quotes are the anthropologist Dr. John Murdoch, reproduced by Stefansson].

Another argument I sometimes hear is that the Inuit are genetically adapted to their high-fat diet, and the same food would kill a European. This appears not to be the case. The anthropologist and arctic explorer Vilhjalmur Stefansson spent several years living with the Inuit in the early 20th century. He and his fellow Europeans and Americans thrived on the Inuit diet. American doctors were so incredulous that they defied him and a fellow explorer to live on a diet of fatty meat only for one year, under the supervision of the American Medical Association. To the doctors' dismay, they remained healthy, showing no signs of scurvy or any other deficiency (JAMA 1929;93:20–2).

Yet another amazing thing about the Inuit was their social structure. Here's Dr. John Murdoch again (quoted from Cancer, Disease of Civilization):

The women appear to stand on a footing of perfect equality with the men, both in the family and the community. The wife is the constant and trusted companion of the man in everything except the hunt, and her opinion is sought in every bargain or other important undertaking... The affection of parents for their children is extreme, and the children seem to be thoroughly worthy of it. They show hardly a trace of fretfulness or petulance so common among civilized children, and though indulged to an extreme extent are remarkably obedient. Corporal punishment appears to be absolutely unknown, and children are rarely chided or punished in any way.

Unfortunately, those days are long gone. Since adopting a modern processed-food diet, the health and social structure of the Inuit has deteriorated dramatically. This had already happened to most groups by Weston Price's time, and is virtually complete today. Here's Price:

In the various groups in the lower Kuskokwim seventy-two individuals who were living exclusively on native foods had in their 2,138 teeth only two teeth or 0.09 per cent that had ever been attacked by tooth decay. In this district eighty-one individuals were studied who had been living in part or in considerable part on modern foods, and of their 2, 254 teeth 394 or 13 per cent had been attacked by dental caries. This represents an increase in dental caries of 144 fold.... When these adult Eskimos exchange their foods for our modern foods..., they often have very extensive tooth decay and suffer severely.... Their plight often becomes tragic since there are no dentists in these districts.

Modern Inuit also suffer from very high rates of diabetes and overweight. This has been linked to changes in diet, particularly the use of white flour, sugar and processed oils.

Overall, the unique lifestyle and diet of the Inuit have a lot to teach us. First, that humans are capable of being healthy as carnivores. Second, that we are able to thrive on a high-fat diet. Third, that we are capable of living well in extremely harsh and diverse environments. Fourth, that the shift from natural foods to processed foods, rather than changes in macronutrient composition, is the true cause of the diseases of civilization.

New Low-carb Study

I know you’ve all heard the news about the new low-carb study in the New England Journal of Medicine by now, but I have to chime in. I‘m going to try to offer you a different perspective of the study that you may not have found elsewhere. First of all, this is a Rolls Royce of a study. It was large, well-controlled, and two years long. It was partly funded by the Atkins foundation, but it's a peer-reviewed study in a good journal and if anything the study design is slanted against the low-carbohydrate diet.

The study compared the weights and various health parameters of 322 overweight subjects put on one of three diets: a “low-fat diet”, a Mediterranean diet and a “low-carbohydrate diet”. The first two were calorie-restricted while the low-carb diet was not. First of all, the “low-fat” diet was not particularly low in fat. It was 30% fat by calories, only a few percent short of the US average. What they call low-fat in the study is actually a calorie-restricted version of the American Heart Association diet recommendation, which suggests:

“…30% of calories from fat, 10% calories from saturated fat, and an intake of 300 mg of cholesterol per day. The Participants were counseled to consume low-fat grains, vegetables, fruits, and legumes and to limit their consumption of additional fats, sweets and high-fat snacks.”

So henceforth, I’ll refer to it as the AHA diet rather than the low-fat diet.

The “low-carb” diet wasn’t particularly low in carbohydrate either. The low-carb group was only getting 10% fewer calories from carbohydrate than the low-fat or Mediterranean diet groups. Despite these problems, the low-carbohydrate diet was the most effective overall. It caused a weight loss of 5.5 kg (12 lb), compared to 4.6 kg (10 lb) and 3.3 kg (7.4 lb) for the Mediterranean and AHA diets, respectively.

One of the most amazing aspects of the study is that the low-carb diet was the only one that wasn’t calorie-restricted, yet it caused the most weight loss. People in the low-carb group naturally reduced their calorie intake over the course of the study, ending up with an intake similar to the AHA group.

The low-carb diet also came out on top in most of the markers of health they examined. It caused the largest drop in HbA1c, a measure of average blood glucose level. It caused the largest drop in C-reactive protein, a measure of inflammation (the Mediterranean diet also did well). And finally, it caused the biggest improvement in the triglyceride:HDL ratio. This ratio is the best blood lipid predictor of heart disease risk I’m aware of in modern Western populations. The lower, the better. They didn't calculate it in the study so I had to do it myself. Here's a graph of the change in trig:HDL ratio for each group over the course of the study:


Other interesting findings: despite the calorie restriction, diabetic participants on the AHA group actually saw a significant increase in fasting blood glucose.

I've speculated before that wheat and sugar may cause hyperphagia, or excessive eating. We can see from these results that reducing carbohydrate (and probably wheat) reduces overall caloric intake quite significantly. This squares with the findings of the recent Chinese study that showed an increase in calorie intake and weight, correlating with the replacement of rice with wheat as the primary carbohydrate. It also squares with diet trends in the US, where wheat consumption has risen alongside calorie intake and weight.

I'd love to know what the results would have looked like if they had gone on a true low-carbohydrate diet, or even simply eliminated grains and sugar.

Mortality and Lifespan of the Inuit

One of the classic counter-arguments that's used to discredit accounts of healthy hunter-gatherers is the fallacy that they were short-lived, and thus did not have time to develop diseases of old age like cancer. While the life expectancy of hunter-gatherers was not as high as ours today, most groups had a significant number of elderly individuals, who sometimes lived to 80 years and beyond. Mortality came mostly from accidents, warfare and infectious disease rather than chronic disease.

I found a a mortality table from the records of a Russian mission in Alaska (compiled by Veniaminov, taken from Cancer, Disease of Civilization), which recorded the ages of death of a traditionally-living Inuit population during the years 1822 to 1836. Here's a plot of the raw data:

Here's the data re-plotted in another way. I changed the "bin size" of the bars to 10 year spans each (rather than the bins above, which vary from 3 to 20 years). This allows us to get a better picture of the number of deaths over time. I took some liberties with the data to do this, breaking up a large bin equally into two smaller bins. I also left out the infant mortality data, which are interesting but not relevant to this post:


Excluding infant mortality, about 25% of their population lived past 60. Based on these data, the approximate life expectancy (excluding infant mortality) of this Inuit population was 43.5 years. It's possible that life expectancy would have been higher before contact with the Russians, since they introduced a number of nasty diseases to which the Inuit were not resistant. Keep in mind that the Westerners who were developing cancer alongside them probably had a similar life expectancy at the time. Here's the data plotted in yet another way, showing the number of individuals surviving at each age, out of the total deaths recorded:


It's remarkably linear. Here's the percent chance of death at each age:


In the next post, I'll briefly summarize cancer data from several traditionally-living cultures other than the Inuit.

Cancer Among the Inuit

I remember coming across a table in the book Eat, Drink and Be Healthy (by Dr. Walter Willett-- you can skip it) a few years back. Included were data taken from Dr. Ancel Keys' "Seven Countries Study". It showed the cancer rates for three industrialized nations: the US, Greece and Japan. Although specific cancers differed, the overall rate was remarkably similar for all three: about 90 cancers per 100,000 people per year. Life expectancy was also similar, with Greece leading the pack by 4 years (the data are from the 60s).

The conclusion I drew at the time was that lifestyle did not affect the likelihood of developing cancer. It was easy to see from the same table that heart disease was largely preventable, since the US had a rate of 189 per 100,000 per year, compared to Japan's 34. Especially since I also knew that Japanese-Americans who eat an American diet get heart disease just like European-Americans.

I fell prey to the same logic that is so pervasive today: the idea that you will eventually die of cancer if no other disease gets you first. It's easy to believe, since the epidemiology seems to tell us that lifestyle doesn't affect overall cancer rates very much. There's only one little glitch... those epidemiological studies compare the sick to the sicker.

Here's the critical fact that modern medicine seems to have forgotten: hunter-gatherers and numerous non-industrial populations throughout the world have vanishingly small cancer rates. This fact was widely accepted in the 19th century and the early 20th, but has somehow managed to fade into obscurity. I know it sounds unbelievable, but allow me to explain.

I recently read Cancer, Disease of Civilization by Vilhjalmur Stefansson (thanks Peter). It really opened my eyes. Stefansson was an anthropologist and arctic explorer who participated in the search for cancer among the Canadian and Alaskan Inuit. Traditionally, most Inuit groups were strictly carnivorous, eating a diet of raw and cooked meat and fish almost exclusively. Their calories came primarily from fat, roughly 80%. They alternated between seasons of low and high physical activity, and typically enjoyed an abundant food supply.

Field physicians in the arctic noted that the Inuit were a remarkably healthy people. While they suffered from a tragic susceptibility to European communicable diseases, they did not develop the chronic diseases we now view as part of being human: tooth decay, overweight, heart attacks, appendicitis, constipation, diabetes and cancer. When word reached American and European physicians that the Inuit did not develop cancer, a number of them decided to mount an active search for it. This search began in the 1850s and tapered off in the 1920s, as traditionally-living Inuit became difficult to find.

One of these physicians was captain George B. Leavitt. He actively searched for cancer among the traditionally-living Inuit from 1885 to 1907. Along with his staff, he performed 50,000 examinations a year for the first 15 years, and 25,000 a year thereafter. He did not find a single case of cancer. At the same time, he was regularly diagnosing cancers among the crews of whaling ships and other Westernized populations. It's important to note two relevant facts about Inuit culture: first, their habit of going shirtless indoors. This would make visual inspection for external cancers very easy. Second, the Inuit generally had great faith in Western doctors and would consult them even for minor problems. Therefore, doctors in the arctic had ample opportunity to inspect them for cancer.

A study was published in 1934 by F.S. Fellows in the U.S Treasury's Public Health Reports entitled "Mortality in the Native Races of the Territory of Alaska, With Special Reference to Tuberculosis". It contained a table of cancer mortality deaths for several Alaskan regions, all of them Westernized to some degree. However, some were more Westernized than others. In descending order of Westernization, the percent of deaths from cancer were as follows:


Keep in mind that all four of the Inuit populations in this table were somewhat Westernized. It's clear that cancer incidence tracks well with Westernization. By "Westernization", what I mean mostly is the adoption of European food habits, including wheat flour, sugar, canned goods and vegetable oil. Later, most groups also adopted Western-style houses, which incidentally were not at all suited to their harsh climate.

In the next post, I'll address the classic counter-argument that hunter-gatherers were free of cancer because they didn't live long enough to develop it.

Masai and Atherosclerosis

I've been digging deeper into the health of the Masai lately. A commenter on Chris's blog pointed me to a 1972 paper showing that the Masai have atherosclerosis, or hardening of the arteries. This interested me so I got my hands on the full text, along with a few others from the same time period. What I found is nothing short of fascinating.

First, some background. Traditional Masai in Kenya and Tanzania are pastoralists, subsisting on fermented cow's milk, meat and blood, as well as traded food in modern times. They rarely eat fresh vegetables. Contrary to popular belief, they are a genetically diverse population, due to the custom of abducting women from neighboring tribes. Many of these tribes are agriculturalists. From Mann et al: "The genetic argument is worthless". This will be important to keep in mind as we interpret the data.

At approximately 14 years old, Masai men are inducted into the warrior class, and are called Muran. For the next 15-20 years, tradition dictates that they eat a diet composed exclusively of cow's milk, meat and blood. Milk is the primary food. Masai cows are not like wimpy American cows, however. Their milk contains almost twice the fat of American cows, more protein, more cholesterol and less lactose. Thus, Muran eat an estimated 3,000 calories per day, 2/3 of which comes from fat. Here is the reference for all this. Milk fat is about 50% saturated. That means the Muran gets 33% of his calories from saturated fat. This population eats more saturated fat than any other I'm aware of.

How's their cholesterol? Remarkably low. Their total serum cholesterol is about half the average American's. I haven't found any studies that broke it down further than total cholesterol. Their blood pressure is also low, and hypertension is rare. Overweight is practically nonexistent. Their electrocardiogram readings show no signs of heart disease. They have exceptionally good endurance, but their grip strength is significantly weaker than Americans of African descent. Two groups undertook autopsies of male Masai to look for artery disease.

The first study, published in 1970, examined 10 males, 7 of which were over 40 years old. They found very little evidence of atherosclerosis, even in individuals over 60. The second study, which is often used as evidence against a high-fat diet, was much more thorough and far more interesting. Mann et al. autopsied 50 Masai men, aged 10 to 65. The single most represented age group was 50-59 years old, at 13 individuals. They found no evidence of myocardial infarction (heart attack) in any of the 50 hearts. What they did find, however, was coronary artery disease. Here's a figure showing the prevalence of "aortic fibrosis", a type of atherosclerotic lesion:


It looks almost binary, doesn't it? What could be causing the dramatic jump in atherosclerosis at age 40? Here's another figure, of total cholesterol (top) and "sudanophilia" (fatty streaks in the arteries, bottom). Note that the Muran period is superimposed (top).


There's clearly a pattern here. Either the Masai men are eating nothing but milk, meat and blood and they're nearly free from atherosclerosis, or they're eating however they please and they have as much atherosclerosis as the average American. There doesn't seem to be much in between.

Here's a quote from the paper that sums it up well:

We believe... that the Muran escapes some noxious dietary agent for a time. Obviously, this is neither animal fat nor cholesterol. The old and the young Masai do have access to such processed staples as flour, sugar, confections and shortenings through the Indian dukas scattered about Masailand. These foods could carry the hypothetical agent."

I know this blog is starting to sound like a broken record, but I'll say it again: you can eat a wide variety of foods and be healthy, except industrial grain products (particularly wheat), sugar, industrial vegetable oil and other processed food. The Masai are just one more example of a group that's healthy when eating a traditional diet.

What to do if Your Study Contradicts Conventional Wisdom

I just read a recent paper from the British Journal of Sports Medicine, "Daily Energy Expenditure and Cardiovascular Disease Risk in Masai, Ruran and Urban Bantu Tanzanians". The study caught my eye because I think we have a lot to learn from healthy traditionally-living populations worldwide.

The Masai have a very unique diet consisting almost exclusively of whole cow's milk, cow's blood and meat. As you might imagine, they eat a lot of fat, a lot of saturated fat and a modest amount of carbohydrate (from lactose). They also have low total cholesterol, low blood pressure, and virtually no overweight. They have been a thorn in the side of the lipid hypothesis for a long time.

The Bantu are an agricultural population that traditionally eat a diet low in fat and high in carbohydrate. Their staples are root vegetables, corn, beans, fish and wild game. The paper also describes a group of urban Bantu, which eats a diet intermediate in fat and carbohydrate. Incidentally, the investigators describe it as a "high-fat diet", despite the fact that the percentage fat is about the same as what Americans and Europeans eat, shamelessly exposing their bias.

The investigators recorded the three groups' diets, activity levels, physical characteristics and various markers of cardiovascular disease risk. Here's what they found: only 3% of Masai were obese, compared to 12% of rural Bantu and 34% of urban Bantu (they'd fit right in here!). The Masai, despite smoking like chimneys, had generally lower CVD risk factors than the other two populations, with the urban Bantu being significantly worse off than the rural Bantu.

Overall, the Masai came out looking really good, with the rural Bantu not too far behind. The urban Bantu look almost as bad as Americans. How do we make sense of these two conflicting facts? 1) The urban Bantu eat an amount of fat and saturated fat that's right in the middle of what the Masai and the rural Bantu eat, yet they seem the most likely to keel over spontaneously. 2) Saturated fat KILLS!! Answer: keep digging until you find something else to blame your results on.

They certainly did find something, and it's the reason the study was published in the British Journal of Sports Medicine rather than the American Journal of Clinical Nutrition. The Masai exercise more than either of the other two groups. I don't have too much trouble believing that. However, the authors used a dirty trick to augment their result: they normalized calorie expenditure to body weight. They present their data as kcal/kg/day. In other words, the fatter you are, the lower your apparent energy expenditure! It makes no sense to me. But it does inflate the apparent exercise of the Masai, simply because of the fact that they're thinner than the other two groups.

Due to this unscrupulous number massaging, here's what they got (data re-plotted by me):


I'm going to try to un-massage the data. Here's what it looks like when I factor bodyweight out of the equation. Calories expended (above resting metabolic rate) is on the Y-axis. The bars look a bit closer together...



Here's what it looks like when you add back resting metabolic rate. I assumed 1500 kcal/day. This graph is an approximation of their total energy expenditure per day:



Hmm, the differences keep getting smaller, don't they? I'm not challenging the fact that the Masai exercise more than the other two groups, but I do have a problem with this kind of manipulation of the data in misleading ways.

Their conclusion is that exercise is protecting the Masai from the deadly saturated fats in their diet. A more parsimonious explanation is that saturated fat per se doesn't cause heart disease. It's also more consistent with other healthy cultures that ate high-fat diets like the Inuit, certain Australian aboriginal groups, and some American Indian groups. It's also consistent with the avalanche of recent trials of low-carbohydrate diets, in which people consistently see improvements in weight, blood pressure, and CVD markers, among other things. Not that I have much faith in blood lipid markers of CVD.

My conclusion, from this study and others, is that macronutrients don't determine how healthy a diet is. The specific foods that compose the diet do. The rural Masai are healthy on a high-fat diet, the rural Bantu are fairly healthy on a low-fat, high carbohydrate diet. Only the urban Bantu show a pattern really consistent with the "disease of civilization", despite a daily energy expenditure very similar to the rural Bantu. They're unhealthy because they eat too much processed food: processed vegetable oil, processed grain products, refined sugar.

Thanks to kevinzim for the CC photo

Low-carb Review Article

The other day, I came across this nice review article from the American Journal of Clinical Nutrition. It gives a thorough but accessible overview of the current state of research into carbohydrate-restricted diets, without all the fatophobic mumbo-jumbo. It points out a few "elephants in the room" that the mainstream likes to ignore. First of all, the current approach isn't working:

The persistence of an epidemic of obesity and type 2 diabetes suggests that new nutritional strategies are needed if the epidemic is to be overcome.

Preagricultural diets were low in carbohydrate:

In contrast to current Western diets, the traditional diets of many preagricultural peoples were relatively low in carbohydrate (1, 2). In North America, for example, the traditional diet of many First Nations peoples of Canada before European migration comprised fish, meat, wild plants, and berries. The change in lifestyle of several North American aboriginal populations occurred as recently as the late 1800s, and the numerous ensuing health problems were extensively documented (3-5). Whereas many aspects of lifestyle were altered with modernization, these researchers suspected that the health problems came from the change in nutrition—specifically, the introduction of sugar and flour.

Carbohydrate reduction leads to a normalization of appetite:

It may also be that the mere lowering of serum insulin concentrations, as is seen with LCDs, may lead to a reduction in appetite. In support of this idea, several studies have found that insulin increases food intake, that foods with high insulin responses are less satiating, and that suppression of insulin with octreotide leads to weight loss (27-29).

I can't believe it; all that fat isn't going to clog my arteries??

Several outpatient diet studies have shown reductions in CVD risk factors after an 8–12-wk LCKD, during weight loss, and during weight maintenance (21, 60-62).

The last paragraph is a zinger:

We emphasize that strategies based on carbohydrate restriction have continued to fulfill their promise in relation to weight loss and that, contrary to early concerns, they have a generally beneficial effect on most markers of CVD, even in the absence of weight loss. In combination with the intuitive and established efficacy in relation to glycemic control in diabetics, some form of LCD may be the preferred choice for weight reduction as well as for general health.

Thoughts on Obesity, Part II

In my reading, I've come to the conclusion that, in some people, overweight may be a type of carbohydrate intolerance.

Insulin is the master hormone that orchestrates the metabolic changes that cause fat accumulation. It instructs the body to transport glucose and fat from the blood into the cells. It tells the liver to synthesize fat from sugar. It inhibits the release of fat from fat cells. There are no other hormones that have a similar range of effects.

Insulin is the "storage hormone". Don't believe me? Ask a type I diabetic. Type I diabetes happens when the pancreas no longer secretes insulin. These people are rail-thin until they are given insulin injections, at which point they often gain excess weight. Many deliberately skip injections to lose weight. Unfortunately, this has serious consequences as it allows their blood glucose to rise to dangerous levels unchecked.

If insulin is kept low, fat synthesis and storage are inhibited, and fat release from fat cells is increased. Carbohydrate is particularly effective at elevating insulin, acutely and chronically. As carbohydrate digests, it's broken down into glucose, which enters the bloodstream. The pancreas releases insulin in an attempt to keep blood glucose within a healthy range, and the storage begins. Refined carbohydrate is the worst offender, because it causes a large and rapid rise in blood glucose.

Regular overconsumption of carbohydrate causes insulin to be chronically elevated in many people [update- I no longer believe this is true. I now believe that only certain types of carbohydrate- namely wheat and sugar- cause a pathological increase in fasting insulin over time]. This comes along with "insulin resistance", whereby most or all tissues become desensitized to insulin. This is the tissues' way of saying "Stop! My energy stores are already full! I can't handle any more glucose or fat!".

Some people are able to maintain normal insulin levels (and sensitivity) in the face of a high-carbohydrate diet. This is probably partly genetic and partly environmental. Certain people, for whatever reason, have fat tissue that is prone to fat accumulation. It could be because they oversecrete insulin, or because their fat tissue is sensitive to the action of insulin, but probably both. It likely has to do with a combination of insulin resistance in non-fat tissue, and insulin sensitivity in fat tissue. Inactivity and fructose consumption (from corn syrup or sucrose) are also high on the list of suspects.

Fat tissue is typically the last to become insulin resistant because it acts as a valuable buffer to remove excess (and potentially toxic) glucose from the bloodstream. Unfortunately, simply being thin is not a reliable indicator that your body tolerates carbohydrate well. It can indicate either that all tissues are insulin-sensitive and insulin levels are low, or all tissues (including fat) are insulin resistant and insulin levels are high. The latter scenario leads to type II diabetes, pronto.

Since fat accumulation revolves around carbohydrate intake and insulin production, it makes sense that reducing carbohydrate causes weight loss. No more carbohydrate = a lot less glucose, and a lot less insulin to deal with it. This completely sidesteps the problem of insulin resistance, although that seems to respond favorably to carbohydrate restriction as well. Every time true low-carbohydrate diets are matched head-to-head with reduced-calorie, carbohydrate-rich diets, subjects lose more weight and have fewer problems with hunger on the low-carbohydrate diet. I discussed a recent study here.

The idea that you can achieve and maintain a healthy weight without cutting calories sounds too good to be true. In fact, all it represents is a return to our natural pattern of eating as human beings. It may involve breaking an addiction to carbohydrate. True hunter-gatherers eat between 0 and 35% of their calories as carbohydrate, and no refined carbohydrate [correction: a number of hunter-gatherer groups ate more than 35% carbohydrate, typically from starchy tubers]. In industrial nations, we eat approximately 50% of our calories as carbohydrate. Hunter-gatherers also exercise regularly, and don't eat Frosted Sugar Bombs for breakfast. This helps maintain good insulin sensitivity. Since we are genetically very similar to our hunter-gatherer ancestors, we would be wise to learn from their example.