|Van Campen, Darrell
Submitted to: Nutrition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/1996
Publication Date: N/A
Interpretive Summary: Zinc deficiency is a problem for some population groups in the USA. Because plant foods are generally considered to be poor sources of dietary zinc, increasing the amount and improving the bioavailability of zinc in cereal grains and grain-based food products is important since these foods will comprise increasingly larger portions of the diet as people understand the USDA food pyramid and accept current dietary recommendations calling for increased consumption of cereals. Grain and grain-based products provide only about 13% of the zinc consumed by people in the USA, and much of the zinc may not be absorbed because of antinutritional factors in the diet. This study indicates that the bioavailability of zinc in diets that contain plant proteins may be enhanced up to 30% by supplemental dietary methionine, an amino acid that contains sulfur. Methionine increased the absorption of dietary zinc provided either as an inorganic salt or that which occurred naturally in corn kernels. Also, corn kernels with methionine-rich proteins had higher concentrations of zinc than did normal kernels. Selection of seeds and grains with increased amounts of methionine may also increase the amount and bioavailability of zinc and thereby increase the nutritional value of the foods.
Technical Abstract: A whole-body radioassay method was used to assess effects of supplemental dietary methionine (Met) on absorption by rats of zinc (Zn) provided in test meals labeled either extrinsically or intrinsically with 65Zn. Intrinsically labeled meals contained corn (Zea mays L.) harvested from two genotypes grown in 65Zn-labeled nutrient solutions. Corn genotypes had kernels with either normal amounts of Met (Nor-Met corn) or kernels with methionine-rich proteins (High-Met corn). Rats fed extrinsically labeled meals absorbed 57, 67, 73 and 71% of the 65Zn dose when a soy- based diet (15% protein) contained either 0, 1, 2 or 3 g of supplemental Met/kg diet, respectively. Zinc absorption was not affected by supplemental Met when protein was provided by egg whites. Dietary Met enhanced absorption by rats of intrinsic 65Zn in both the Nor-Met and the High-Met corn. The bioavailability to rats of Zn in the kernels was similar regardless of the Met content of the corn. However, the concentration of Zn in the High-Met kernels (30 ug/g) was greater than that in the Nor-Met corn (22 ug/g) so that rats fed the High-Met corn ingested and absorbed more Zn from test meals than did rats fed the Nor- Met corn. We suggest that the carrier-mediated component of Zn absorption may not function optimally in animals fed low-Zn diets that are also deficient in sulfur amino acids. Apparently, the Met status of experimental animals may be an important consideration in studies conducted to assess Zn bioavailability. Selection of seeds and grains with increased amounts of Met may enhance Zn bioavailability and thereby increase the nutritional value of staple plant foods.