Leptin plasma levels as a marker of sparing-energy mechanisms in obese women.

OBJECTIVE: To investigate possible relationships between leptin and energy expenditure (EE), both in the condition of stable body weight and during weight loss.
SUBJECTS: Seventy four Caucasian, adult obese women with stable body weight (including 10 obese women studied before and during a body weight-reducing program). MEASUREMENTS: Resting EE (REE) and substrate oxidation rates by indirect calorimetry; plasma leptin concentrations by radioimmunoassay (RIA).
RESULTS: In conditions of stable body weight, leptin values showed a significant, negative relationship with REE, as expressed in absolute values (P = 0.030) and as adjusted for the variation in lean body mass (LBM) (P = 0.017). This negative relationship was independent of both LBM and fat mass (FM). Linear regression analysis was used to obtain the equation linking REE and LBM; then both predicted REE and the percent deviation from predicted REE were calculated for each subject. Leptin values were negatively related (P < 0.0001) to the deviation from predicted REE. During active body weight loss, the modifications of both REE (delta REE) and lipid oxidation (delta lipid oxidation) were significantly negatively related to leptin concentrations, which were measured before the dieting period (P < 0.03 for both).
CONCLUSION: In obese women, high plasma leptin concentrations are associated with a low rate of REE, when body weight is stable, and with a reduction of REE and lipid oxidation, in response to a hypocaloric diet. This suggests that, in severely obese women, leptin is a marker of sparing energy mechanisms operating in both basal and reducing weight conditions.