Association between serum γ-glutamyltransferase and dietary factors: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

Background: Diet may be involved in the strong dose-response relation of γ-glutamyltransferase (GGT) concentration with incident diabetes. Objective: We examined dietary correlates of serum GGT activity. Design: Study subjects were 3146 black and white men and women aged 17-35 y in 1985-1986. A diet history was taken at years 0 and 7. Food items were classified into alcohol; breaded, battered, or canned vegetables; fruit; fruit juice; refined grain; whole grain; dairy; legumes; meat; poultry; fish; fresh or frozen vegetables; nuts; and coffee. Results: After adjustment for nondietary factors and other food groups, GGT was positively associated with alcohol consumption and meat intake. Geometric means of year 10 GGT across categories of alcohol consumption (0, 1-9, 10-19, 20-29, and ≥ 30 g/d) were 17.7, 18.8, 20.4, 21.8, and 24.8 U/L (P for trend < 0.01); corresponding means across quintiles of meat intake were 19.2, 20.2, 20.5, 21.8, and 21.2 times/wk (P for trend < 0.01). GGT was inversely associated with fruit intake. Among possible meat constituents, dietary heme iron, but not saturated fat, was associated with GGT. Dietary constituents typical of plant foods showed an inverse association. In contrast, vitamin supplements were positively associated with GGT. Conclusions: Serum GGT activity increased in a dose-response manner as alcohol and meat consumption increased and fruit consumption decreased. Heme iron contained in meats and micronutrients contained in fruits may influence GGT metabolism. However, micronutrients taken as supplements had a positive association with GGT.