There is widespread consensus that regular consumption of fruits and vegetables is associated with a reduced risk of developing cancer. Evidence comes both from cohort studies and case control studies. In a cohort study a population is followed and lifestyle factors are documented, generally relying on questionnaires. Subjects who eventually come down with a disease are then compared with those who have remained healthy. In a case- control study, patients who have been diagnosed with a disease are compared with a control group matched in terms of age and socioeconomic factors. Again by means of questionnaires, attempts are made to tease out factors that may be responsible for causing the disease in question.
Many, but not all cohort and case-control studies have revealed that fruit and vegetable consumption affords a protective effect against cancer. Data become even more meaningful when a number studies are pooled together in a “meta analysis.” Indeed in one analysis of 16 case-control and 3 cohort studies, subjects who ate lots of vegetables had a 25% lower breast cancer risk than those who ate few vegetables. High fruit consumption was associated with a 6% decrease in risk. It would of course be interesting to explore which specific fruits or vegetables have the greatest anti-cancer effect. Does an apple a day, for example, keep the oncologist away? Maybe. There are indications that apples just might throw a stumbling blog in the way of cancer. In a giant case-control study in Italy, involving some 6000 cancer patients and an equal number of controls, subjects who ate one or more apples a day had a reduced risk of every kind of cancer. Of course we have to be very careful about jumping to premature conclusions here, because eating apples may be just a marker for a healthier lifestyle. What is really needed is an experiment whereby subjects are given a chemical that has the ability to induce cancer, and are then given varying amounts of apples to see if this has any effect on tumour development. Obviously this cannot be done with humans, but it can be done with rats. And it has been done!
Researchers at Cornell University designed a study with five groups of rats, 30 rats in each group, to investigate this very effect. Four of the groups were treated with dimethylbenzanthracene, a potent carcinogen, and the fifth group served as a control. One of the experimental groups got no apple supplements in the diet, while the other three groups had the human equivalent of one, three or six apples a day pumped into their stomach every day for 24 weeks. The rats that had not been exposed to the carcinogen developed no tumours at all. In the other three groups tumours did develop, as was to be expected. But the exciting finding was that the incidence of tumours was in proportion to the amount of apples eaten! In the group that had not been treated with apple extract, 71% of the rats developed tumours but only 60% of the animals in the “one apple” group did so. The “three apple” cohort had a 43% incidence and the “six apple” group only 40%. If you’re a rat, an apple a day really keeps the oncologist away!