While diets have become the craze around the world, the effect of diets on energy expenditure has intrigued scientists.
In an examination of the effect on energy expenditure and components of the metabolic syndrome of 3 types of commonly consumed diets following weight loss, decreases in resting energy expenditure and total energy expenditure were greatest with a low-fat diet, intermediate with a low-glycemic index diet, and least with a very low-carbohydrate diet, suggesting that a low-fat diet may increase the risk for weight regain compared to the other diets, according to preliminary research published in the June 27 issue of JAMA
"Many people can lose weight for a few months, but most have difficulty maintaining clinically significant weight loss over the long term. According to data from the National Health and Nutrition Examination Survey (1999-2006), only 1 in 6 overweight and obese adults report ever having maintained weight loss of at least 10 percent for 1 year," according to background information in the article. One explanation for the poor long-term outcome is that weight loss elicits biological adaptations—specifically a decline in energy expenditure and an increase in hunger—that promote weight. According to the authors, the effect of dietary composition on energy expenditure during weight-loss maintenance has not been studied.
Cara B. Ebbeling, Ph.D., of Children's Hospital Boston, and colleagues conducted a study to evaluate the effects of 3 weight-loss maintenance diets on energy expenditure, hormones, and components of the metabolic syndrome. The study, conducted between June 2006 and June 2010, included 21 overweight and obese young adults. After achieving 10 percent to 15 percent weight loss while consuming a run-in diet, participants consumed an isocaloric low-fat diet (60 percent of energy from carbohydrate, 20 percent from fat, 20 percent from protein; high glycemic load), low-glycemic index diet (40 percent from carbohydrate, 40 percent from fat, and 20 percent from protein; moderate glycemic load), and very low-carbohydrate diet (10 percent from carbohydrate, 60 percent from fat, and 30 percent from protein; low glycemic load) in random order, each for 4 weeks. The primary outcome measured was resting energy expenditure (REE), with secondary outcomes of total energy expenditure (TEE), hormone levels, and metabolic syndrome components.
The researchers found that energy expenditure during weight-loss maintenance differed significantly among the 3 diets. The decrease in REE from pre-weight-loss levels, measured by indirect calorimetry in the fasting state, was greatest for the low-fat diet (average relative to baseline, -205 kcal/d), intermediate with the low-glycemic index diet (-166 kcal/d), and least for the very low-carbohydrate diet (-138 kcal/d). The decrease in TEE also differed significantly by diet (average -423 kcal/d for low fat; -297 kcal/d for low glycemic index; and -97 kcal/d for very low carbohydrate).
"Hormone levels and metabolic syndrome components also varied during weight maintenance by diet (leptin; 24-hour urinary cortisol; indexes of peripheral and hepatic insulin sensitivity; high-density lipoprotein [HDL] cholesterol; non-HDL cholesterol; triglycerides; plasminogen activator inhibitor 1; and C-reactive protein), but no consistent favorable pattern emerged," the authors write.
"The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective," the researchers write. "TEE differed by approximately 300 kcal/d between these 2 diets [very low-carbohydrate vs. low-fat], an effect corresponding with the amount of energy typically expended in 1 hour of moderate-intensity physical activity."
"These findings suggest that a strategy to reduce glycemic load rather than dietary fat may be advantageous for weight-loss maintenance and cardiovascular disease prevention. Ultimately, successful weight-loss maintenance will require behavioral and environmental interventions to facilitate long-term dietary adherence. But such interventions will be most effective if they promote a dietary pattern that ameliorates the adverse biological changes accompanying weight loss," the researchers conclude.