Serum beta-glucuronidase activity is inversely associated with plant-food intakes in humans

Beta-glucuronidase hydrolyzes glucuronide moieties from steroids and xenobiotics, such that circulating glucuronyl conjugates can interact with target tissues. In animal models, dietary constituents can alter beta-glucuronidase activity. In humans, serum beta-glucuronidase activity reflects liver enzyme loss during cell turnover, and thus is a surrogate for hepatic beta-glucuronidase. We recruited 83 men and 120 women, who were nonsmokers, 20-40 y of age, with self-reported vegetable and fruit (V&F) intakes of < or = 2.5 or > or = 4.5 servings/d. Diet was assessed by 3-d food record and serum carotenoids were measured as biomarkers of V&F intake (e.g., servings V&F vs. alpha-carotene; r = 0.47, P = 0.0001). Serum beta-glucuronidase activity (Modified Sigma Units/L), determined in blood samples collected on two consecutive days from fasting subjects, was higher in men than women (mean +/- SEM: 20.4 x 10(3) +/- 1.0 x10(3) and 17.0 x 10(3) +/- 0.6 x 10(3), P = 0.002). beta-Glucuronidase activity (adjusted for sex) was inversely associated with intakes of plant protein, fruit, dietary fiber (r = -0.24 to -0.30; P < 0.001), botanical groupings Cucurbitaceae, Rosaceae, and Leguminosae (r = -0.16 to -0.19; P < 0.05), and serum alpha- and beta-carotene and beta-cryptoxanthin (r = -0.18 to -0.26; P < or = 0.01). Activity was not associated with overall vegetable intake. Although these associations are modest, the data suggest that plant foods, particularly constituents of fruits and fiber-containing foods, may influence human beta-glucuronidase activity in a potentially favorable direction.