Effect of Foods, Including Rice, Miso Soup, and Japanese Tea, on the Absorption of Zinc

Only approximately 30% of ingested zinc (Zn) is absorbed. Some foods consumed with Zn affect its intestinal absorption. Zn supplementation is generally recommended immediately after meals to minimize gastric irritation. In this study, we examined the effects of food intake on Zn absorption. Zn acetate (25 mg as zinc) was administered orally to 13 healthy young volunteers either in the fasting state or with foods, such as 150 g of brown rice, white rice, beef hamburg, 200 mL of miso soup (fermented soybean paste soup), seaweed soup, cow's milk, Japanese tea and orange juice (100% fruit juice). Blood samples were collected before and at 1, 2, 3, and 4 h after administration of Zn alone, food alone (without Zn), or food with Zn. Zn absorption was compared using the area under the curve. The results showed that serum Zn levels hardly increased when Zn was administered with brown rice, whereas the Zn level was not inhibited by coadministration with seaweed soup. The absorption of Zn acetate with other foods was reduced to 14-66% compared to that when Zn was administered alone. Our results suggest that brown rice, which is a popular food in Japan and other countries, is associated with decreased Zn absorption.