There is growing awareness that the profound changes in the envi- ronment (eg, in diet and other lifestyle conditions) that began with the introduction of agriculture and animal husbandry 10 000 y ago occurred too recently on an evolutionary time scale for the human genome to adjust. In conjunction with this discordance between our ancient, genetically determined biology and the nutritional, cultural, and activity patterns of contemporary Western populations, many of the so-called diseases of civilization have emerged. In particular, food staples and food-processing procedures introduced during the Neolithic and Industrial Periods have fundamentally altered 7 cru- cial nutritional characteristics of ancestral hominin diets: 1) glyce- mic load, 2) fatty acid composition, 3) macronutrient composition, 4) micronutrient density, 5) acid-base balance, 6) sodium-potassium ratio, and 7) fiber content. The evolutionary collision of our ancient genome with the nutritional qualities of recently introduced foods may underlie many of the chronic diseases of Western civilization. Am J Clin Nutr 2005;81:341–54.