Energy-metabolism adaptation in obese adults on a very-low-calorie diet.

In this study, six obese women received a very-low-calorie diet (VLCD) for 3 wk. At day 0, body composition was assessed with a bioelectric impedance analyzer. The evolution in lean body mass (LBM) during the VLCD was estimated from nitrogen balance, measuring urine and fecal losses and taking into account skin, nitrate, and menstrual losses to avoid underestimation bias that could explain the decreased ratio of resting metabolic rate (RMR) to LBM previously reported. RMR was measured at days 0, 3, 5, and 21. The RMR-LBM ratio declined significantly during the VLCD period and decreased faster during the first week; the day 3, day 5, and day 21 ratio values were 94%, 91%, and 82%, respectively, of the original. The RMR-LBM ratio decrease after 21 d of a VLCD was near that found in chronic undernutrition. Results of previous studies that did not find any drop in the RMR-LBM ratio in obese adults on VLCDs might be explained by their LBM-assessment methods.