Dietary composition and physiologic adaptations to energy restriction

Abstract

Background: The concept of a body weight set point, determined predominantly by genetic mechanisms, has been proposed to explain the poor long-term results of conventional energy-restricted diets in the treatment of obesity.

Objective: The objective of this study was to examine whether dietary composition affects hormonal and metabolic adaptations to energy restriction.

Design: A randomized, crossover design was used to compare the effects of a high-glycemic-index (high-GI) and a low-glycemic-index (low-GI) energy-restricted diet. The macronutrient composition of the high-GI diet was (as percent of energy) 67% carbohydrate, 15% protein, and 18% fat and that of the low-GI diet was 43% carbohydrate, 27% protein, and 30% fat; the diets had similar total energy, energy density, and fiber contents. The subjects, 10 moderately overweight young men, were studied for 9 d on 2 separate occasions. On days -1 to 0, they consumed self-selected foods ad libitum. On days 1-6, they received an energy-restricted high- or low-GI diet. On days 7-8, the high- or low-GI diets were consumed ad libitum.

Results: Serum leptin decreased to a lesser extent from day 0 to day 6 with the high-GI diet than with the low-GI diet. Resting energy expenditure declined by 10.5% during the high-GI diet but by only 4.6% during the low-GI diet (7.38 +/- 0.39 and 7.78 +/- 0.36 MJ/d, respectively, on days 5-6; P = 0.04). Nitrogen balance tended to be more negative, and energy intake from snacks on days 7-8 was greater, with the high-GI than the low-GI diet.

Conclusion: Diets with identical energy contents can have different effects on leptin concentrations, energy expenditure, voluntary food intake, and nitrogen balance, suggesting that the physiologic adaptations to energy restriction can be modified by dietary composition.

FIGURE 1

Mean (± SEM) weight loss from baseline during 6 d of energy restriction. Baseline weight for the high-glycemic-index diet (○) was 98.5 ± 2.7 kg and for the low-glycemic-index diet (◆) was 99.2 ± 2.9 kg (NS; n = 10).

FIGURE 2

Glycemic (A) and insulinemic (B) responses measured at 0.5-h intervals. Curves are mean (± SEM) values after breakfast, lunch, and dinner on day 1. Columns represent area under the concentration-versus-time curve calculated by using the trapezoidal rule. Actual baseline blood glucose for the high-glycemic-index (high-GI) diet (○) was 5.5 ± 0.2 mmol/L and for the low-glycemic-index (low-GI) diet (◆) was 5.3 ± 0.2 mmol/L (NS; n = 10).

FIGURE 3

Mean (± SEM) daily fasting serum leptin as a percentage of baseline values. Baseline serum leptin for the high-glycemic-index diet (○) was 14.9 ± 1.7 mg/L and for the low-glycemic-index diet was 13.4 ± 1.2 mg/L (NS; n = 10).

FIGURE 4

Mean (± SEM) daily resting energy expenditure with the high- (○) and low- (◆) glycemic-index diets (n = 10).