This section is from the "Health and Survival in the 21st Century" book, by Ross Horne.
People become vegetarians to improve their health and extend their lives. Some vegetarians go a step further and consume their food mainly uncooked, while others go even further and limit their diet to fruit, which they claim to be the natural food of man.
Their argument is sound for a number of reasons, but one way or the other it is a fact that, in reasonable variation, fruit can provide the full complement of all required nutrients in adequate quantities, remembering that the requirement for protein and fat are much lower than generally believed. Therefore, instead of being considered merely an accessory to conventional meals, fruit should be considered in its own right as a staple food. The advantages of a fruitarian diet are:
That fruit alone can ideally sustain human health and vigor, even without drinking water, indicates that it indeed provides the basis of man's natural diet. Further substantiation of this view is that there are about forty distinct anatomical, physiological and biological features of humans which show unquestionably that the human body is designed mainly for a fruit diet, notwithstanding the fact that, like all animals, they can survive less successfully on a wide variety of foods. These features range from natural fondness for sweet foods, jaw and teeth structure, salivary secretion, length of digestive tract, size of pancreas, stereo color vision and so on. In fact, in all these respects humans are practically identical today with the other higher primates in the wild which, whenever possible, live on fruit.
Evidence of the suitability of fruit as a staple food and not just as an accessory to the conventional diet is to be seen by observing fruitarians who live entirely on a wide variety of fresh fruit, and who display lean youthful bodies, low blood pressure, clear vision and unimpaired faculties, even with advancing years.
A well-known human peculiarity never before connected with this argument but which provides almost conclusive evidence is that humans, like all primates, are incapable of making vitamin C in their bodies, whereas other animals can (excepting guinea pigs and fruit-eating bats). Basing their argument on this fact, it is strongly advocated by many authorities that people should take large amounts of supplementary Vitamin C to compensate for this "error of Nature", which they put down to an unfavorable mutation in our evolutionary past some millions of years ago. To prove this "unlucky mutation" argument completely wrong, and at the same time prove that man is a natural fruit eater, consider:
Therefore it is clear that the human diet ideally should be based mainly on fresh fruit, and that past errors which have led to widespread vitamin C deficiencies are dietary--not genetic--errors.