III.3 - Nutritional Chemistry

Summary

The idea that diet is an important factor in health is a very old one and, if anything, had greater prominence in the time of Hippocrates than it does now. However, the development of a workable system or science of nutrition had to await the development of modern chemistry with its significant advances at the end of the eighteenth century. Before that time, the purpose of nutrition in adults was assumed to be the replacement of abraded (or worn-out) tissues. Meat, the tissues of other animals, seemed an effective food for this purpose, because it provided essentially like-for-like, but vegetable foods seemed to be made of quite different “stuff.” Animal tissues allowed to decompose became putrid and alkaline, whereas most vegetables became acid and did not become putrid. When heated and dried, animal tissues became hornlike, whereas vegetables became powdery. However, Iacopo Bartolomeo Beccari of the University of Bologna pointed out in 1728 that, when sieved (i.e., debranned) wheat flour was wetted and pummeled into a dough and then kept under running water until the floury starch had been washed out, the residual gluten had all the properties of animal tissues. Similar fractions were found in other plant foods. It was thought that these were the essential nutrients, and it was the job of the digestive system to winnow away the unwanted starch, fiber, and so forth and leave the glutenlike material to be circulated in the blood, for patching and filling.

Protein

With the discovery of nitrogen as an element toward the end of the eighteenth century, and the development in France of methods for analyzing the amount of nitrogen in different materials, came the discovery that both animal tissues and the “animal-like” fractions in vegetables contained nitrogen, whereas starch, sugar, fats, and vegetable fibers contained only carbon, hydrogen, and oxygen.