The purpose of this study was to examine the hypothesis that the antiobesity effect of doenjang, a Korean fermented soy paste is different between the mutant and the wild-type alleles of a polymorphism upstream of the uncoupling protein-1 (UCP-1) gene in overweight subjects. In our randomized, double-blind, placebo-controlled trial, a total of 51 subjects with a body mass index of 23 kg/m(2) or greater and a waist-to-hip ratio of 0.90 or greater for men or 0.85 or greater for women were randomly assigned to take 9.9 g/d of either a placebo or doenjang for 12 weeks. The relative frequency of the mutant G allele of the UCP-1 polymorphism was 0.60 in the placebo group and 0.62 in the doenjang group. Supplementation of doenjang had no significant effect on the visceral fat area compared with that of the placebo group, but there was a significantly reduced amount of visceral fat in subjects with the G allele of UCP-1 polymorphism. Doenjang supplementation was found to significantly increase the free fatty acid concentration in subjects with both the A allele and the G allele. There was a significant association between visceral fat and age in study subjects with both the wild-type and mutant alleles of the UCP-1 gene. Doenjang supplementation significantly reduced visceral fat and increased the free fatty acid concentrations in subjects with the G allele of the UCP-1 polymorphism, which suggests that doenjang may be related to increased free fatty acid levels caused by elevated lipolysis in these subjects.
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