Diet and Cancer
Many studies have tried to determine whether specific foods increase or decrease a person's risk of getting cancer. Unfortunately, different studies have had conflicting results, so it is hard to know what effect foods or dietary supplements have on cancer risk. A common problem is that when studies find that people who eat more of a certain food seem to have lower rates of a certain cancer, it can be difficult to tell whether those people also were different in terms of other risk factors (such as where they live, how much they smoke and drink, and so forth). Often, when doctors do a controlled trial (see also The Science of Medicine) and randomly give some people a seemingly helpful food or supplement, the studies do not show a beneficial effect. Some foods and supplements have been studied more than others, and many studies are ongoing.
Alcohol increases the risk of cancers of the mouth, throat, esophagus, liver, breast, and the colon and rectum. People who smoke as well as drink have a much higher risk of these cancers. Although some studies have shown that moderate intake of alcohol, especially wine, decreases the risk of heart disease, this potential benefit must be weighed against the potential risks of alcohol.
Antioxidants, such as vitamins C and E and beta-carotene ( vitamin A), are part of a well-balanced diet. However, studies have not shown that taking supplements containing these antioxidants decreases the risk of cancer. There is some evidence that taking high doses of beta-carotene or vitamin E supplements may actually increase the risk of certain types of cancer.
In some older studies, folate (folic acid) was found to help protect against colon cancer and breast cancer. However, more recent studies have found that folic acid supplements may actually increase the risk of prostate cancer, colorectal cancer, and possibly breast cancer. Most people get sufficient folate in their diets and do not need to take supplements.
People who eat large amounts of processed meats may be at risk for stomach and colon and rectal cancers. Some investigators attribute this finding to nitrates, which are in luncheon meats, hams, and hot dogs. This connection is unproved. Eating meats processed by salting or smoking may increase exposure to potential cancer-causing substances.
Some studies have found higher rates of some types of cancers in countries where fat intake is higher. However, no studies have found that decreasing fat intake decreases the risk of cancer. Of more importance, however, is that foods that contain high levels of saturated fats also contain many calories and may contribute to obesity, which is a risk factor for cancer and other health problems.