An extract or concentrate is always to be treated with suspicion—it can so easily upset the balance of an otherwise reasonable diet—and it may be a concentrate of the wrong part of the original food.

A classic example of this was provided some years ago by a synthetic vitamin-D product. Using spectroscopic analysis to control their process, the firm’s chemists were able to attain a higher concentration of "vitamin-D" than previously thought possible. The only snag was that when the stuff was put on the market it caused several deaths and a large number of less serious poisonings.

Even where synthetically-prepared vitamins or vitamin concentrates are administered without apparent ill-effect, they do not behave as vitamins in their natural form. In almost monotonous succession the "vitamins" which were so intensively prescribed by the medicos only a few years ago are being found ineffective. For a vitamin to perform its proper function in the body, the orthodox physiologist now finds that it requires the presence and co-operation of many other substances. These other factors occur—strangely!—in the natural foods which contain the vitamin, and the modern teaching is that vitamins are not simple substances, but "complexes". Each consists of two, three or dozens of more-or-less related compounds. In practice, the only way to ensure reliable and useable supplies of any particular vitamin in swallowable form is to eat the whole food in which it occurs.