The effect of picolinic acid supplementation on zinc absorption by men fed a low tryptophan diet
1988
Five men were fed a diet composed of conventional foods but designed to be limiting in tryptophan (approximately 235 mg/day), and with an average zinc content of 2.8 +/- 0.4 mg/day. Subjects consumed the low tryptophan diet for 5-7 weeks and then the same diet supplemented with picolinic acid, 10 mg/day, for 4-7 weeks. Zinc balance was near zero throughout the study and was unaffected by the dietary treatment. Zinc absorption was measured using an oral dose of the stable isotope 67Zn given in a flavored glucose drink once during each dietary period after an overnight fast. Thus, each subject served as his own control. There was a significant increase in zinc absorption during the picolinic acid supplementation period (p = 0.05). There were no significant differences in urinary or fecal zinc excretion, plasma zinc, or serum alkaline phosphatase between dietary periods, although plasma zinc fell in 4 of 5 subjects when picolinic acid was fed. Increased zinc absorption caused by picolinic acid was apparently offset by increased zinc turnover resulting in unchanged balance, Picolinic acid affects zinc metabolism in normal humans fed diets low in zinc and limited in tryptophan.
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