The effect of calorie deficits of 25 percent, 40 percent and 55 percent on adaptation to resting energy expenditure and lean mass in healthy post-menopausal women
Susan Fullmer1, Bridget L. Reed1, Dennis L. Eggett2, Robert T. Davidson1, and Nora K. Nyland1
1Nutrition, Dietetics and Food Science, and 2Statistics, Brigham Young University, Provo, Utah, USA

Abstract

Background: Metabolic adaptation seen in caloric restriction has not been reported as a percent caloric deficit. Objectives: To determine if metabolic adaptation would occur within a range of three caloric deficits and to determine the nature of the dose-response relationship between caloric restriction and degree of metabolic adaptation. Design: Twenty-six subjects were randomly assigned to receive a 25%, 40%, or 55% caloric deficit diets for three weeks. Metabolic rate, body composition and serum leptin and thyroid hormones were measured. Statistical analysis: Analysis of variance and analysis of covariance were used to test for significant differences between groups. Post-hoc analysis was completed using Tukey-Kramer. Results: All three diets resulted in significant declines in resting energy expenditure (REE), total weight, fat mass, and lean mass; however there were no significant differences between groups. Declines in REE due to metabolic adaptation were (LSM±SE): 105.2±25.0 (p=0.0004), 118.1±27.0 (p=0.0002), and 72.6±26.1 (p=0.012) kcals/day, for 25%, 40%, and 55% diets; respectively. All three means were significantly different than zero, suggesting metabolic adaptation; however they were not significantly different from each other (p=0.17). Changes in REE were not related to changes in T3 or leptin (p=0.41, p=0.50). Due to baseline differences we were not able to measure a  dose-response relationship between metabolic adaptation and degree of caloric restriction. Conclusions: All three caloric deficits resulted in significant losses in body weight, lean mass, and metabolic adaptation to REE. We conclude that more severe caloric restrictions result in more rapid weight loss without an increased detriment to REE than less severe restrictions; but more research is needed to confirm this finding. However, severe caloric restrictions also resulted in greater losses in lean mass. Obesity and Metabolism 2009; 5: 121-128.

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