The discovery of the chief nutrients has been essentially a twentieth-century phenomenon. In 1897, Dutch researcher Christian Eijkman, while investigating beriberi in the Dutch East Indies, showed that a diet of polished rice caused the disease and that the addition of the rice polishings to the diet cured it. Fifteen years later, Polish chemist Casimir Funk proposed that not only beriberi but scurvy, pellagra, and rickets were caused by an absence of a dietary substance he called vitamine; and the age of vitamins was under way.

This is not to say that much earlier research did not undergird such twentieth-century breakthroughs. The importance to human health of some minerals, such as iron, had long been at least vaguely recognized, and by 1800, it was understood that blood contained iron; since the eighteenth century, some kind of dietary deficiency had been a periodic suspect as the cause of scurvy; and protein was discovered in the nineteenth century. But in addition to both water- and fat-soluble vitamins, the importance and functions of most of the major minerals and the trace minerals, along with amino acids, were all twentieth-century discoveries, as were the essential fatty acids and the nutritional illness now called protein–energy malnutrition (PEM).

One important consequence of the new knowledge was the near-total eradication of the major deficiency diseases. Pellagra, which had ravaged southern Europe and the southern United States, was found to be associated with niacin deficiency; beriberi, the scourge of rice-consuming peoples in the Far East, was linked with thiamine deficiency; and scurvy was finally – and definitively – shown to be the result of vitamin C deficiency.