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Can Where Your Calories Come From Tell How Much Weight You'll Lose?

A lab-controlled study finds high-fat, low-carb diets to be effective in staving off weight loss. But how about in the real world?

Food Politics
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As the co-author of a recent book called Why Calories Count: From Science to Politics, I am well aware of how difficult it is to lose weight.

The problem

  • When you are dieting and losing weight, you require fewer calories to maintain and move your smaller body, and your metabolism and muscle activity -- and, therefore, your total energy expenditure-slow down.
  • To maintain the weight loss, you need to eat less than you did before you began dieting.

But what would happen if you could adjust your diet to keep your energy expenditure from slowing down?

Enter Ebbeling et al in JAMA, with a comprehensive study to address precisely that question. The results of the study and editorial comments on the findings demonstrate how complicated and difficult it is to obtain definitive answers to questions about diet composition and calorie balance.

  • The investigators asked whether calorie-controlled diets containing varying amounts of carbohydrate, fat, and protein, and varying in glycemic load (a measure of rapidly absorbable carbohydrates in foods) affected total energy expenditure in obese people who had just lost 10% to 15% of their weight, but were still obese.
  • They found that the diet lowest in carbohydrate did not slow down energy expenditure as much as did the low-glycemic index diet, or the one lowest in fat.
  • They concluded: "The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective."

This study took years and involved a very large number of state-of-the-art physiological measurements.

But I want to focus on the question of whether calories from all sources are metabolically equivalent. Here's my understanding of the study.

The methods

Ebbeling et al started by offering $2500 to obese volunteers to participate in a 7-month weight-loss trial. In my view, the 21 subjects who finished the study worked hard for that money.

They had to participate sequentially in a:

  • Weight-monitoring phase for 4 weeks, during which they ate their typical diets while the investigators monitored their weight.
  • Weight-loss phase for 12 weeks, during which they were fed pre-prepared diets calculated to contain about 60% of their usual calorie intake so they would lose about 2 pounds a week. The average weight loss over 12 weeks was an impressive 14.3 kg (31.5 pounds).
  • Weight-stabilization phase for 4 weeks, during which they were fed pre-prepared diets that provided the reduced number of calories needed to maintain their newly reduced weights.
  • Testing phase of 4 weeks on each of three pre-prepared test diets (total: 12 weeks). All three test diets provided the number of calories needed to maintain the reduced weight. During each of the 3 testing periods, investigators measured--not estimated--the subjects' total daily energy expenditure (resting metabolism plus activity).

The composition of the diets

DIETS CARB% FAT% PROTEIN% DECREASE IN TOTAL ENERGY EXPENDITURE, Calories/Day
Weight-loss 45 30 25 Not reported
Low-fat (high-carb) 60 20 20 ~400
Low-Glycemic Index 40 40 20 ~300
Very low carb (high-fat) 10 60 30 ~100

Note that whenever one component of a diet gets changed, the other two components change too. Because protein usually occurs in foods in relatively low amounts, a low-fat diet is necessarily a high-carbohydrate diet, and vice versa.

Presented by

Marion Nestle is a professor in the Department of Nutrition, Food Studies, and Public Health at New York University. She is the author of Food Politics, Safe Food, What to Eat, and Pet Food Politics. More

Nestle also holds appointments as Professor of Sociology at NYU and Visiting Professor of Nutritional Sciences at Cornell. She is the author of three prize-winning books: Food Politics: How the Food Industry Influences Nutrition and Health (revised edition, 2007), Safe Food: The Politics of Food Safety (2003), and What to Eat (2006). Her most recent book is Feed Your Pet Right: The Authoritative Guide to Feeding Your Dog and Cat. She writes the Food Matters column for The San Francisco Chronicle and blogs almost daily at Food Politics.

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