The human diet has evolved from that of the hunter-gatherer, through that of the subsistence agriculturalist, to that of the urban-dweller in an industrialized society. The differences between the former diet and the so-called 'affluent' diet of developed countries are shown in Figure 5. The increased intake of macronutrients and decreased intake of dietary fibre have been accompanied by increased incidence of diseases such as diabetes, heart disease, and some cancers. A more healthful diet, relatively higher in carbohydrate and dietary fibre, and lower in fat and alcohol, is advocated by most nutritionists.

The amounts of nutrients suggested for a healthful diet cover quite wide ranges of values, which are compatible not only with survival, but also with optimal health. Not only do individuals differ from each other in their nutrient needs, but also any one person's requirements may change with age, as shown in Figure 6.