Including diet as a possible cause of cancer is relatively recent. Some researchers have suggested that the incidence of certain kinds of cancer may relate to the amount of fat in our diets. Much animal experimentation has shown that when caloric intake is decreased, the incidence of cancer is lowered. It appears that cancer, like other degenerative diseases, may strike hardest the overfed.
For instance, Japan, where the diet is still predominately based on fish and rice and contains substantially less fat than does the American or European diet, has both a lower incidence of cancer and a substantially different profile in types of cancers than the other industrialized countries. Since the incidence of cancer goes up sharply among Japanese living in the United States, as discussed earlier, some researchers have settled on differences in diet as a likely explanation.
There are factors other than diet that might explain the low rate in Japan compared to other industrial nations. Cultural factors, for instance, may play a critical role since they, more than diet, influence the way we live, our beliefs and feelings. Still, many nonfat-eating Japanese get cancer and many fat-eating Westerners don't.
There are other population studies that cast doubt on the theory of diet as a sole cause. One of the strangest findings of cancer research comes from studies comparing disease incidence among institutionalized catatonic schizophrenics with institutionalized paranoid schizophrenics.
Catatonia is a form of mental illness in which individuals wall themselves off from outside contact. Typically, catatonics do not speak nor do they give any sign of recognition that they have been spoken to. Frequently, they will not take the initiative to eat or perform any other necessary physical function. They isolate and protect themselves from the outside world. (They are also, it should be pointed out, protected from the outside world.) Their susceptibility to cancer is very low.
Unlike the catatonics who tune out the world, paranoids are overly sensitive to the reactions of everyone around them— they often suspect that everybody is plotting against them. The incidence of cancer among paranoid schizophrenics is higher than that of the normal population. It would appear that the ability of the catatonic to close out the world provides some form of protection against factors that may influence cancer, whereas the paranoid has no such protection.
The relationship between these two special populations and the argument that diet has something to do with the incidence of cancer is as follows. In institutions, both kinds of patients, catatonics and paranoids, receive the same diet yet have sharply different incidences of cancer. In addition, they receive a diet very similar to the general diet in the United States, yet the incidence of cancer for both groups is different from that of the population at large. An explanation having to do with the psychology of people rather than the nature of diets is necessary to account for these differences.
Still, the fact that another population has a low incidence of cancer and eats a typical Western diet does not eliminate the possiblity that Japan's incidence rates are related to diet. Instead, it suggests that we take a second look at what makes Japan distinctive. Although the Japanese diet is certainly unique among the industrialized nations, it is clear that Japanese culture is also unique. As feelings and beliefs are acknowledged to play a role in disease, then cultural factors may assume overwhelming importance in creating different rates of cancer incidence, since cultural patterns train people in their beliefs and feelings.