Physiological and biochemical variables associated with body fat loss in overweight women

During a weight loss study conducted on a metabolic unit, five women lost an average of 8.7 +/- 0.7 kg of body fat mass (FM) with a 12 week treatment of low energy diet plus exercise. Another group of five women lost 4.4 +/- 0.7 kg FM with a 12 week treatment of an adequate diet plus exercise. Within each treatment, the amount of FM lost varied by approximately 2-fold. To explain the variability in FM loss, we tested its association by multiple regression analysis with several physiological and biochemical measurements obtained during a 2 week stabilization period or early in the treatment period. The variable most closely correlated with FM loss was plasma free fatty acid levels following exercise (EX-FFA). This variable alone accounted for 79 percent of the variation in FM loss. EX-FFA was simple to measure and was repeatedly correlated with FM loss, whether FFA values of the first exercise test or EX-FFA values obtained later in the experimental period were used. Of the physiological variables tested, the rate of fat calories expended in response to a test meal was correlated with FM loss and accounted for 71 percent of the variation. Upon subsequent testing, however, this relationship was not repeatable. When a treatment group designation (dummy-coded variable) was added to the regression analysis, the rate of fat calories expended at rest (FATRMR) was related to FM loss. Together, FATRMR and the dummy-coded variable accounted for 87 percent of the variation in FM loss. In a separate multiple regression equation, the combination of EX-FFA and the dummy-coded variable also accounted for 87 percent of the variation in FM loss. Further evaluation of these relationships is required to determine if EX-FFA or FATRMR would be useful as predictors of FM loss under conditions of weight loss where individuals are living freely in the community and consuming a variety of diets.