A twin study of genetic and environmental influences on the intake of fluids and beverages.

The heritability of fluid and beverage intake was investigated with 109 identical and 86 fraternal adult twin pairs who were paid to maintain 7-day diaries of everything they either ate or drank. Both classical analysis of heritability and linear structural modeling revealed that the amount of fluids ingested daily or in bouts is strongly influenced by heredity in males and by familial environment in females. This was true for the total amount of water ingested, regardless of source, the amount of fluid ingested in excess of digestive requirements, and the amount ingested in the form of drinks. Linear structural modeling revealed that these influences act primarily on the overall total intake of fluids and affect drink fluid intake only indirectly. Significant influences of the genes and the environment were also found on the ingestion of particular beverages, independent of the effects of age and the total intake of fluids. In particular, significant genetic influences were identified on the intake of alcohol, sugared soda, coffee, and milk, and significant familial environmental influences on the intake of diet soda and fruit juice. These results suggest that both the amounts and the types of fluids ingested are complexly influenced by heredity and the environment, depending upon the gender of the individual and the type of beverage investigated.