Leptin may influence sweet taste sensitivity. However, there are no reports on an association between the sweet taste threshold and serum leptin levels during weight loss in humans. We investigated the changes in the sweet taste threshold and the serum leptin levels during a weight-loss program, in connection with a leptin receptor polymorphism (Lys109Arg) that may be related to insulin and glucose metabolism. The study included 20 obese, but otherwise healthy, females (mean age: 55 +/- 7 years, body mass index: 26.1 +/- 1.7 kg/m(2)). Participants completed a 12-week weight-loss program based on energy restriction through diet and exercise, which aimed at achieving their optimal weight. The sweet taste threshold was determined according to the whole-mouth gustatory method. Genetic analyses were performed using the allele-specific DNA assay. Serum leptin levels were decreased from 9.2 +/- 4.5 to 7.9 +/- 4.9 ng/ml (p = 0.014) after body weight loss. The sweet taste threshold also decreased significantly from 0.59 +/- 0.42 to 0.22 +/- 0.20% in a solution of sucrose (p = 0.004). In contrast, there were no differences in changes of the threshold between participants with and without the Lys109 allele. A multiple regression analysis revealed that the changes in serum leptin levels were significantly correlated with those in the sweet taste threshold, independent of the initial threshold levels and the Lys109 allele. In conclusion, the serum leptin levels are decreased significantly during a weight-loss program in obese females, which may be associated with the decrease in the sweet taste threshold.
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