Dose-dependent inhibitory effect of phenolic compounds in foods on nonheme-iron absorption in men.

Nonheme-iron absorption from a typical Southeast Asian meal was studied to examine the effect of a common vegetable, Yod Kratin, which contains a considerable amount of iron-binding phenolic groups. Yod Kratin (leaves of the lead tree) is a very popular vegetable in Thailand. It is consumed at least once a week year round, sometimes every day, together with the main meal. With a common portion size of the vegetable (20 g), iron absorption was reduced by almost 90%. As little as 5 g inhibited iron absorption by 75%. Addition of ascorbic acid partly counteracted inhibition. Adding 100 mg ascorbic acid reduced inhibition of iron absorption from 5 g Yod Kratin by half and the inhibition from 10 g Yod Kratin by a quarter. The study illustrates the marked effect of iron-binding phenolic compounds on iron nutrition and, thus, the importance of acquiring knowledge of the content of such compounds in different foods.

Rice and iron absorption in man.

Several studies suggest that iron absorption is low from rice-based meals. Comparisons of the effect of rice starch and wheat starch on iron absorption showed that rice had no effect on absorption. Observed differences in effects on iron absorption between different batches of rice starch could be explained by differences in the phytate content. Phytate is always present in rice grains. The content varies markedly depending on the method of milling. In polished rice, the content of phytate-P varied between 11.5 and 66 mg/100 g rice (data from 45 rice mills in Thailand). The bioavailability of iron in a meal composed of meat, a vegetable and rice varied about threefold (22.1-7.5 per cent) depending on the different phytate content of the rice (4 levels between 30 and 175 mg phytate-P were studied). The inhibitory effect of the phytate in rice was overcome by adding different amounts of an ascorbic acid-rich vegetable (green collard) to the meals.