Weight loss and change in resting metabolic rate.

The relation between change in resting metabolic rate (RMR) and change in fat-free mass (FFM) after weight loss is not well understood and is often inappropriately expressed in kilocalories per unit of FFM. We measured RMR and FFM in 35 obese patients enrolled in a conservative weight-loss program. RMR per kilogram FFM was not different after weight loss. However, the regression of delta RMR on delta FFM revealed that the decline in RMR tended to be greater than could be accounted for by loss of FFM. At initial test and retest, body fat (Fat) was not a predictor of RMR after FFM had been taken into account but delta Fat significantly contributed to the prediction of delta RMR when added to the equation after delta FFM. Thus, people losing larger amounts of weight had declines in RMR greater than could be accounted for by loss of FFM. Self-reported age of onset of obesity was not related to delta RMR.