Researchers do not believe that most forms of cancer are caused directly by what we eat. Studies do show, however, diet can be a powerful weapon in the fight against cancer. This is because some dietary changes have been found to prevent cancer or at least reduce the aggressiveness of the disease.
What are these dietary weapons and how can we use them to protect ourselves from cancer?
Recent research has provided strong evidence that eating fish regularly as an adult, or soy as a young girl or using a specific vitamin if you are a smoker, can help to protect against certain cancers. Another study found that high blood cholesterol, which is usually related to a diet high in animal fats, does not determine whether or not a man develops prostate cancer, but lower levels of these lipids may help protect against the more aggressive forms of the disease.
They found that women who ate the most soy-based foods (such as tofu, miso, natto) during ages 5-11 reduced their risk of developing breast cancer by 58 percent, compared to women who ate the least amount. The corresponding reductions for adolescent and adult intake were about 25 percent.
"Childhood soy intake was significantly associated with reduced breast cancer risk in our study, suggesting that the timing of soy intake may be especially critical," said the study's lead investigator, Larissa Korde, M.D., M.P.H. Korde worked in collaboration with epidemiologists at the University of Hawaii, the Northern California Cancer Center and the University of Southern California.
Exactly why this happens is not known. One hypothesis, however, is that soy isoflavones have estrogenic effects that cause changes in breast tissue, leading to decreased sensitivity to carcinogens. A similar protective effect has been found in studies of overweight girls, perhaps because fat tissue also secretes estrogens.
"Hormonal exposures in adulthood, such as use of estrogen and progesterone replacement therapy, are established breast cancer risk factors. However, a growing body of evidence suggests that hormonal exposures early in life may also modify susceptibility to breast cancer," Korde said.
"We already know that eating fish can reduce the risk of sudden cardiac death, and this might provide another reason to add fish to your diet," said Megan Phillips, a doctoral student at the Harvard School of Public Health and the lead author of this study.
The researchers found that compared to men who ate the least amount of fish, the risk of developing colorectal cancer was 40 percent lower in men who ate the most fish, was 20 percent lower in men who ate fish 2-5 times a week and 13 percent lower among participants who ate fish less than two times a week.
They found that male smokers who had high plasma levels of vitamin E had lower levels of oxidative-DNA damage in their white blood cells. Oxidative DNA damage is a mechanism by which tobacco smoking can increase risk of cancer. The investigators did not find a similar effect of vitamin E in women.
"There was a dose-response relationship, in that the more vitamin E we found in the blood of the men, the less there was of this cancer-related biomarker," said the study's senior investigator, Professor Frederica P. Perera of Columbia University School of Public Health.
"This suggests that while working toward the goal of quitting smoking, which is the very best way to prevent development of smoking-related cancers, it could be helpful to eat a diet rich in vitamin E," she said, and added, "we don't yet know why this relationship was not found in women, but a good diet is beneficial to health in many ways."
Vitamin E is found in certain vegetable oils, nuts, whole grains, fish, green leafy vegetables and other foods.
These findings may help explain the earlier discovery that men who used statin drugs experienced half the risk of developing advanced prostate cancer.
"Statin drugs reduce cholesterol in the blood, but they also influence a number of different pathways," said the study's lead researcher, Elizabeth Platz, Sc.D., M.P.H., of the Johns Hopkins Bloomberg School of Public Health. "This study suggests that the ability of statins to lower cholesterol may be important to prostate carcinogenesis, but we are continuing to examine other pathways with which statin drugs interact, such as reduction of inflammation."
Platz cautioned that because the findings come from an observational study, not a trial, it is impossible to conclude that men can lower their risk of developing an aggressive form of prostate cancer by reducing their intake of saturated fat, the type of fat that increases serum cholesterol, which some studies have linked to an increased risk of advanced prostate cancer.
"It is too soon to say that such measures would be specifically beneficial to lowering such a risk, but for good health in general, it is prudent to consume a diet that contains healthful fats that do not increase serum cholesterol," she said.
All of the studies cited above were presented at the American Association for Cancer Research's Frontiers in Cancer Prevention November, 2006 Research Meeting.