A close relationship between coffee intake and certain metabolic disorders is known. Caffeine, one of coffee components, can increase energy expenditure (EE), but there are considerable individual differences in the caffeine effects on EE, and the causes have not been fully established in humans. The Arg allele in the β 3 -adrenergic receptor gene (β 3 -AR), a marker for obesity-related traits, may be a contributor to individual variations in EE. This study investigated the effect of the Arg allele of β 3 -AR on caffeine-induced increases in EE. In 44 healthy young women (21 ± 1 years), physical characteristics, blood pressure, biochemical profiles and dietary nutritional intake were measured. A caffeineloading test was conducted at a dosage of 4 mg per body weight (kg). EE was measured using an indirect open-circuit calorimeter for a 10-min period before, and at 30 min and 60 min after the caffeine-loading test. The β 3 -AR Trp64Arg polymorphism was detected with a PCR-restriction fragment length polymorphism method. The frequency of the Arg allele was 24%. The distribution of the Trp/Trp, Trp/Arg, and Arg/Arg genotypes was 58%, 36%, and 6%, respectively. At the baseline, subjects with the Arg/Arg genotype had a significantly lower EE level than those with the Trp/Trp or Trp/Arg genotype. After the caffeine-loading test, there were caffeine-induced increases in EE in all genotypes, but there were no differences in the levels of increase among the genotypes. These findings suggest that the genotypes of β 3 -AR Trp64Arg polymorphism might be not associated with caffeine-induced increases in EE levels.β 3 -adrenergic receptor; polymorphism; caffeine; energy expenditure; genotype.Tohoku

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