BACKGROUND According to recent reports, individuals with reduced aldehyde dehydrogenase activity may require more energy for the detoxification of aldehydes. Aldehyde dehydrogenase 2 (ALDH2), an ALDH isozyme, is responsible for detoxifying acetaldehyde, an intermediate metabolite of ethanol. Because the variant allele of the rs671 polymorphism of ALDH2 results in a substantial reduction in enzymatic activity, carriers of this variant allele may have a higher energy demand when consuming alcohol than non-carriers. However, no studies have evaluated this phenomenon to date. METHODS To test the hypothesis, we statistically examined the interactive effects between the rs671 and ethanol consumption on energy intake using cross-sectional data from a population-based cohort study, the Japan Multi-Institutional Collaborative Cohort Study, which was conducted in Saga city between 2005-2007 (N = 12,068). RESULTS General linear regression models adjusted for age, sex, ethanol consumption, current smoking status, years of education, dietary restriction, medical history, and physical activity level revealed that energy intake was higher in variant allele carriers than in non-carriers among individuals with alcohol drinking habits, whereas no such correlation was observed among those without drinking habits (≤2 g ethanol/day) (p = 0.03 for interaction between rs671 and ethanol consumption). Energy intake excluding energy from alcoholic beverages, carbohydrate intake, protein intake, and fat intake, showed similar tendencies (p for interaction = 0.01, 0.01, 0.04, and 0.07, respectively). CONCLUSIONS These findings support the hypothesis that increased energy intake is required for the detoxification of aldehydes in individuals with low ALDH activity. This epidemiological evidence provides a possible scientific basis for understanding aldehyde detoxification mechanisms and suggests a novel phenotype of the ALDH2 rs671 polymorphism.