NuSI-funded Study Serves Up Disappointment for the Carbohydrate-insulin Hypothesis of Obesity

A new metabolic ward study tests the idea that lowering insulin via severe carbohydrate restriction increases metabolic rate and accelerates fat loss, independently of calorie intake. Although carbohydrate restriction did modestly increase metabolic rate, it actually slowed fat loss. One of the details that sets this study apart from previous studies is that it was funded by the Nutrition Science Initiative, an organization that was founded specifically to test the insulin hypothesis of obesity and related concepts.

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More Thoughts on the Recent Low-fat vs. Low-carb Metabolic Ward Study

The recent low-carb vs. low-fat study has provoked criticism from parts of the diet-health community. Let's examine these objections and see how they hold up to scientific scrutiny.
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A New Human Trial Undermines the Carbohydrate-insulin Hypothesis of Obesity, Again

The carbohydrate-insulin hypothesis of obesity states that carbohydrates (particularly refined carbohydrates and sugar) are the primary cause of obesity due to their ability to increase circulating insulin, and that the solution to obesity is to restrict carbohydrate intake. Numerous studies have tested this hypothesis, more or less directly, in animals and humans. Despite the fact that many of these studies undermine the hypothesis, it remains extremely popular, both in the popular media and to a lesser extent among researchers. A new human trial by Kevin Hall's research team at the US National Institutes of Health offers very strong evidence that the carbohydrate-insulin hypothesis of obesity is incorrect. At the same time, it offers surprising and provocative results that challenge prevailing ideas about diet and weight loss.

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Does high protein explain the low-carb "metabolic advantage"?

In 2012, David Ludwig's group published a paper that caused quite a stir in the diet-nutrition world (1). They reported that under strict metabolic ward conditions, weight-reduced people have a higher calorie expenditure when eating a very low carbohydrate diet (10% CHO) than when eating a high-carbohydrate diet (60% CHO)*.

In other words, the group eating the low-carb diet burned more calories just sitting around, and the effect was substantial-- about 250 Calories per day. This is basically the equivalent of an hour of moderate-intensity exercise per day, as Dr. Ludwig noted in interviews (2). The observation is consistent with the claims of certain low-carbohydrate diet advocates that this dietary pattern confers a "metabolic advantage", allowing people to lose weight without cutting calorie intake-- although the study didn't actually show differences in body fatness.

In Dr. Ludwig's study, calorie intake was the same for all groups. However, the study had an important catch that many people missed: the low-carbohydrate group ate 50 percent more protein than the other two groups (30% of calories vs. 20% of calories). We know that protein can influence calorie expenditure, but can it account for such a large difference between groups?

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Recent Interviews

For those who don't follow my Twitter account (@whsource), here are links to my two most recent interviews.

Smash the Fat with Sam Feltham.  We discuss the eternally controversial question, "is a calorie a calorie"?  Like many other advocates of the low-carbohydrate diet, Feltham believes that the metabolic effects of food (particularly on insulin), rather than calorie intake per se, are the primary determinants of body fatness.  I explain the perspective that my field of research has provided on this question.  We also discussed why some lean people become diabetic.  Feltham was a gracious host.

Nourish, Balance, Thrive with Christopher Kelly.  Kelly is also an advocate of the low-carbohydrate diet for fat loss.  This interview covered a lot of ground, including the insulin-obesity hypothesis, regulation of body fatness by the leptin-brain axis, how food reward works to increase calorie intake, and the impact of the food environment on food intake.  I explain why I think proponents of the insulin-obesity hypothesis have mistaken association for causation, and what I believe the true relationship is between insulin biology and obesity.  Kelly was also a gracious host.  He provides a transcript if you'd rather read the interview in text form.

Thoughts on the McDougall Advanced Study Weekend

For those of you who aren't familiar with him, Dr. John McDougall is a doctor and diet/health advocate who recommends a very low fat, high starch, whole food vegan diet to control weight and avoid chronic disease. He's been at it for a long time, and he's a major figure in the "plant-based diet" community (i.e., a diet including little or no animal foods).

Dr. McDougall invited me to participate in his 3-day Advanced Study Weekend retreat in Santa Rosa, CA. My job was to give my talk on insulin and obesity, and participate in a panel discussion/debate with Dr. McDougall in which we sorted through issues related to low-carb, Paleo, and the health implications of eating animal foods. I was glad to receive the invitation, because I don't see myself as a diet partisan, and I believe that my evidence-based information is applicable to a variety of diet styles. I saw the Weekend as an opportunity to extend my thoughts to a new community, challenge myself, and maybe even learn a thing or two. It was particularly interesting to compare and contrast the Advanced Study Weekend with the Ancestral Health Symposium, which is more Paleo- and low-carb-friendly.

General Observations

The attendees were a lot older than AHS attendees. I estimate that most of them were in their 60s, although there were some young people in attendance.

I don't place too much emphasis on peoples' personal appearance at conferences like this. You don't know what a person's background, genetics, or personal struggles may be, you don't know how closely they adhere to the program, and you don't know to what degree a group of people might be self-selected for particular traits*. But I will note that Dr. McDougall, his family, and many of the other starch-based/plant-based diet advocates tended to be extremely lean with low fat and muscle mass. They also tended to have a healthy and energetic appearance and demeanor. As I would expect, decades of exceptionally high starch intake hasn't made them obese or obviously ill.

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