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 What Participants Need to Know About Clinical Trials People expect doctors to use treatments that work well and to stop using those that do not. However, it is often difficult for doctors and other scientists to tell which treatments work. Making... read more ) 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. The most convincing evidence is from studies that show diets low in fiber and high in processed meats increase cancer risk. Obesity, regardless of the type of diet, increases the risk of many cancers.
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 increase the risk of certain types of cancer.
Some evidence indicates a higher cancer risk in people with folate (folic acid) deficiency, but whether the deficiency is the cause of cancer is unknown. In contrast, other less conclusive evidence suggests that excess folate may increase cancer risk. A person eating a normal diet requires no additional folate.
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.
The following are English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
American Cancer Society: Stay Healthy: The American Cancer Society provides tips for people to make healthy choices and reduce the risk of cancer
National Cancer Institute: Cancer Causes and Prevention: The National Cancer Institute provides information on nutrients that may be associated with increases or decreases in the risk of cancer