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More miles, fewer biscuits

BMJ 2005; 330 doi: (Published 09 June 2005) Cite this as: BMJ 2005;330:0-h

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Unabsorbed calories, an important consideration.


Almost the whole world believes that too many calories and too little exercise are THE major factors driving the obesity epidemic. Further, since fat contains over twice as many calories as protein or carbohydrate, it is ASSUMED that cutting fat calories will prevent obesity. For example, in Rio state, Brazil, a law banning fat-rich, high-calorie foods in schools came into effect earlier this year. This action follows a trend already under way elsewhere in Brazil. The southern states of Santa Catarina and Rio Grande do Sul also banned high fat foods in an effort to prevent childhood obesity and promote "healthful" eating habits. This legislative action was a response to recent disclosure by a government agency that 1 in 10 Brazilians is Obese due to poor eating habits. Question is, will low-fat eating prevent obesity? Not likely and here's why.

In the introduction to her first book, The Schwarzbein Principle, Endocrinologist Diana Schwarzbein, MD, of Santa Barbara, California remarks, "Both medicine and the media had promoted the belief that eating a low-fat diet while increasing complex carbohydrates caused people to lose body fat and stay healthy. But I had yet to meet anyone who was healthy or thriving on a low-fat diet." Having already experimented with having her diabetic patients reduce carbohydrate and add fat to their diets and seeing them lose weight, Dr. Schwarzbein then "searched the medical literature, looking for studies showing that low-fat diets are healthy" and "was surprised that there are no long-term studies showing such results." Dr. Schwarzbein's clinical experience and journal research eventually resulted in two books recommending increased fat intake and decreased carbohydrate intake to normalize hormone balance.

Other independent researchers (among them biochemists, nutritionists, dentists, medical doctors, etc.) have shown that low-fat diets lead to hormone imbalance, increased appetite, less brown fat activity, and increased calorie absorption efficiency. This last matter of calorie absorption is key to understanding where all the calories go.

Everyone knows that some people can consume high calorie diets without gaining weight while others cannot reduce body fat no matter how much they exercise and restrict calorie intake. An interesting example of high calorie consumption by a sedentary individual that was not resulting in weight gain was broadcast on USA National Public Radio on November 26, 2004. Mary-Ann Beltran, a low-income single mom was enrolled in a research project in which every piece of food she ate the day before was methodically recorded by a researcher, Jenny Donaldson. On the day before the interview, Ms. Beltran had consumed 6,501 calories as calculated by Donaldson. Correspondent Patricia Neighmond's remarked that, "Sixty-five hundred calories is high, particularly when you consider the average daily caloric intake for women of Mary-Ann's age and height is about 2'000 calories. And although Beltran is not overweight now, at age 34, if she keeps eating this way, she's at risk." For me, this interview raises two interesting questions. First, why isn't Beltran already overweight and second, what reason do we have to suspect that she will ever become overweight?

Here's some more interesting observations involving force-feeding studies. In How To Lower Your Fat Thermostat (1983) by D.W. Remington, MD, A.G. Fisher, PhD, and E. A. Parent, PhD, the authors report (page 70) that "In some people, even huge amounts of extra eating will fail to cause weight gain. These people seem to have a weight-regulating mechanism that can vigorously defend the selected weight by wasting huge quantities of excess energy intake." They further observed that any forced weight gain did not last because "subjects will quickly return to pre-study weight even though no continuous effort is made to diet."

On page 71 the authors described a case study in which "A German scientist carefully measured his caloric intake for a full year and noted that he ate an average of 1760 calories per day." For another year he ate an extra 400 calories per day and "At the end of the year, he was still very close to his original weight even though he had eaten enough extra energy to have gained over 40 pounds. He then increased his intake another 600 calories a day for another year without changing his original weight."

There is a possible explanation for this; unabsorbed calories. The digestive tract is a tube open at both ends. Muscular contractions propel food through the tube at various rates depending on the amount of food eaten and on the amount of soluble and insoluble fiber present in the food. Since soluble fiber forms a gel in the intestinal tract, it both slows absorption of digested protein, carbohydrate, and fat into the bloodstream and prevents some calories from being absorbed altogether. Consequently, The unabsorbed calories exit the digestive tract in the fecal material.

Discussion of absorption efficiency on page 78 of How to Lower Your Fat Thermostat: "There is some evidence that the surface area of the gut can be increased by food denial to increase the efficiency of absorption...Rats eating only meal a day have a markedly increased rate of food digestion and absorption. Many obese people also seem to digest food more quickly, perhaps because of dietary efforts and periods of food denial."

I've only read a couple hundred books about weight control so I probably haven't found all existing discussions regarding unabsorbed calories. Here are a few more sources:

The Bio-Diet / 1982 by Luis Guerra, MD pp 27-28.

Why Calories Don't Count / 1982 by Paul Stitt, MS pp 81-82.(1)

What the Bible Says About Healthy Living / 1996 by Rex Russell, MD p 183.(2)

The Doctors Book of Food Remedies / 1998 by Selene Yeager and the Editors of Prevention p 419.

Although research regarding unabsorbed calories is scant and mostly goes unnoticed or is even denied by the scientific community, it is an important consideration that ought to receive more attention by mainstream medical and obesity experts because current advice, based on assumed total absorption of calories into the bloodtstream, is hurting many people who would benefit from increased fat intake.

Journal references:

(1) A. Antonis et. al., "The Influence of Diet on Fecal Lipids in South African White and Bantu Prisoners," American Journal of Clinical Nutrition, Vol. 11, August 1962, pp 142-155.

(2) J.O. Hill, H. Douglas and J.C. Peters, "Obesity Treatment: Can Diet Composition Play a Role?" Annals of Internal Medicine 119(2):7 (1993): 694-697.

David Brown

Nutrition Education Project

Competing interests: None declared

Competing interests: No competing interests

15 June 2005
David E. Brown
Nutrition science information analyst
Self employed carpenter residing at 1925 Belmar Dr., Kalispell, MT 59901, USA