This study was done to elucidate the relationship between postprandial
leptin and
obesity, and the possible influence of the circadian rhythm on the dynamic
leptin response to an oral fat load (OFLT). In experiment 1, we measured the
leptin and
insulin responses to an oral fat load in 16 non-diabetic obese subjects and in 16 healthy controls, matched for age and gender. In experiment 2, we measured the
leptin and
insulin responses to an OFLT according to the time of fat load ingestion: 0700 h (diurnal (D) test) or 2200 h (nocturnal (N) test) in nine normal-weight healthy males. Baseline
leptin concentration was correlated with the body mass index, body fat mass and percentage of body fat mass in both experiments. The
leptin concentrations were higher in women than in men (P<0.001). In experiment 1, the
leptin concentrations were higher in obese subjects than in controls, but did not change over time in either group. The plasma
insulin concentrations at baseline and during the postprandial state, as well as the area under the curve (AUC) of
insulin, were higher in obese subjects than in controls (P<0.05-0. 0001). There was no correlation between postprandial
insulin responses and postprandial
leptin responses in either obese or control groups. In experiment 2,
leptin (D vs N, 2.9+/-1.4 vs 2. 9+/-1.0 ng/ml) and
insulin (D vs N, 41+/-18 vs 25+/-9 pmol/l) concentrations were similar at the beginning of the D and N tests after
a 10 h fast. The
leptin concentrations did not change after D or N tests and were not statistically different for D and N tests. Our results indicate that the
leptin concentration in healthy controls and in obese patients is not acutely influenced by a high fat load.