Technical Abstract: Dietary meat sources (e.g., beef, pork, chicken, and fish) contain substances that promote the bioavailability of iron and zinc from plant foods to humans. These "meat factors" counteract the negative effects of antinutrients (such as phytic acid), which are abundant in edible legume seeds and cereal grains, that reduce the bioavailability of iron and zinc to humans. Possibly, increasing the content of promoter substances in staple plant foods would contribute greatly to reducing iron and zinc deficiencies in poor people especially in those population groups dependent on plant foods for their sustenance. Some data are presented showing that the essential sulfur amino acids, methionine and cysteine, promote zinc bioavailability to rats suggesting that these amino acids may be the promoter substances found in abundance in dietary meat sources. If true, staple plant foods could be bred to contain higher levels of these essential amino acids thereby improving the nutritional quality of these foods with respect to iron and zinc. Such an approach would be a sustainable food-based agricultural approach that could contribute greatly to reducing micronutrient malnutrition globally.