Oct 13, 2007

Gary Taubes on Insulin and Obesity

The new book, "Good Calories, Bad Calories", by Gary Taubes, contains a wealth of information about nutritional research. The book will become famous and controversial, if it hasn't already, because it presents a point of view that is contrary to the medical consensus but growing in popularity (both within and without the medical world). Anyone interested in the science related to intermittent fasting should buy it because it provides a well-documented and thorough review of the science of human nutrition.

Taubes' book argues for the hypothesis that "obesity is caused by the quality of the calories, rather than the quantity, and specifically by the effect of refined and easily digestible carbohydrates on the hormonal regulation of fat storage and metabolism." The theme is that hormones are what matters with respect to obesity and related aspects of health, like heart disease. Insulin is the focus of attention, but glucagon, estrogen, growth hormone and steroids in general are all mentioned in the book. Taubes feels that way too much emphasis has been placed on eating habits. He cites a case where the same person is emaciated above the waist but obese below the waist (yes, there is a picture), and describes mice that will die of starvation without using up fat reserves.

Throughout, he also describes the interpretations given to various observations and experimental results by medical researchers. It's a very interesting case, one that illustrates the importance of going back to the methods and data used in critical experiments.

I bought the book after reading Gina Kolata's review in Sunday's New York Times (Oct. 7). Then, there was then a very interesting article ("Diet and Fat: a Severe Case of Mistaken Consensus" by John Tierney) in Tuesday's science section (Oct. 9). It is interesting to compare that article, which accepts the thesis of the book and focuses on the phenomenon of consensus view that are mistaken, with Kolata's review, which is a bit more skeptical:

"In fact, Taubes convincingly shows that much of what is believed about nutrition and health is based on the flimsiest science....

But the problem with a book like this one, which goes on and on in great detail about experiments new and old in areas ranging from heart disease to cancer to diabetes, is that it can be hard to know what has been left out."
She then cites a study showing that a calorie is a calorie is a calorie; the effect on weight is the same whether from fat or carbohydrate.

I'm inclined to believe that they are both right. It's quite plausible that what really matters is both total calories (because the laws of physics are, after all, inviolable) and how rapidly they lead to an increase in blood glucose (which induces insulin, which leads to the deposition of fat). Ironically, dietary fat, which does not induce insulin, is a preferred source of calories.

What does this have to do with intermittent fasting? I fast three times each week because of evidence that the benefits of caloric restriction (prolonged healthspan) result from the activation of a genetic program rather than from reduced metabolic activity per se, and that this genetic program can also be induced by intermittent fasting. Evidence from animal models for such a genetic program is quite solid. Evidence that this program exists in humans (and it not already fully induced in most people) is less solid. What is really unclear is what that program is and how it can be induced. Much of the science described in Taubes' book will certainly bear on figuring this out.


David Brown said...

One matter that most scientists and weight control experts ignore is the fact that not all calories passing through the digestive tract get absorbed into the bloodstream. Calorie excretion rates as high as 60 percent have been measured by researchers in Africa.

About four years ago, Harvard statistician Penelope J. Greene, PhD presented findings regarding a feeding experiment at the annual meeting of the North American Association for the Study of Obesity. During the 12 week study involving three groups of dieters on different regimens, a low carb group consuming 300 more fat calories per day than either of the other two groups lost more weight than the low-fat group but less weight than the other low-carb group. Dr. Green was not sure how to explain her findings in terms of the laws of thermodynamics. She speculated, "... the body may absorb less of what's eaten on a low-carbohydrate diet which is high in protein and fat." You can access an article about this experiment published in the Harvard Gazette by Googling "Penelope J. Greene."

Most people have a simplistic view of what happens to food as it passes through the digestive tract. The fauna inhabiting the digestive tract feed on the food that doesn't get absorbed and multiply accordingly. It's estimated that half of fecal matter consists of dead bacteria. Anybody who makes compost knows that bacteria generate heat as they feed. So some of the caloric energy in food would be released as heat into the body as bacteria multiply.

To access more of my commentary on this matter, Google "unabsorbed calories" or "calorie excretion."

David Brown
Nutrition Education Project

Dave said...

The "laws of physics are inviolable" argument is often misapplied when it comes to nutrition. To apply conservation of energy, you need to account for all routes of energy output and their possible dependence on energy input. It is assumed that food intake, physical activity, and heat generation are independent. Thus, if physical activity is held constant, and heat is a function of BMR and physical activity only, then excess caloric consumption must lead to fat storage.

Taubes hypothesis, which he supports with some solid science, is that these things are not independent. Different macronutrients have different effects on the metabolism, and thus on the regulation of fat storage, heat generation, and possibly even the urges to perform physical activity and consume more calories. No laws of physics are violated. Rather, we recognize that biological systems are not are considerably more complex than a car engine, containing lots regulatory mechanisms aimed at maintaining allostasis.

Though he doesn't discuss IF directly, I found that Taubes book provided me some extra insight as to how IF can promote weight loss without changing total caloric input.