By Donna Feldman, MS, RD

Cancer is scary business. It seems to strike out of nowhere and affect people of all ages and socioeconomical backgrounds. There are dozens of possible risk factors, from chemical exposure to air pollution to bad genes to old age. Lifestyle choices, including diet and nutrition, are assumed to play a role in cancer risk. But what role? Does a poor diet cause cancer? Can an ideal diet prevent cancer?

Cancer Is Complicated

Cancer is such a complex disease that it is difficult to pin a single cause on a specific cancer. The cancer process goes through many steps, all of which could be affected by some nutritional factors in either good or bad ways. Here is how cancer works: a cell or DNA gets damaged, the damaged cell grows unchecked, and turns into a tumor which spreads and grows uncontrollably. During any one of these steps, a lack of certain nutrients or an excess of some other factor can affect what happens next. Unfortunately, those effects are poorly understood. The most researchers can describe right now is the relationship between nutrition and cancer prevention.

The American Cancer Society recently summed up the current knowledge in this publication. What is the main conclusion? While genes influence your risk of cancer, diet and physical activity levels are the most important lifestyle factors that contribute to cancer.

Obesity Is the Biggest Risk

Obesity is the one dietary factor that is most clearly associated with a higher risk for developing colorectal, breast, endometrial, and other types of common cancers. It is not as simple as saying too much body fat or too many calories causes tumors to appear and grow. In fact, excess weight may just be a marker for some type of diet that contributes to cancer. Overweight people tend to eat more fat and less fiber, so perhaps those 2 nutritional factors are the real cancer risks. Many researchers assumed high fat diets somehow caused cancer and designed studies to show this effect. However, it turned out that this assumption was hard to prove. The exact correlation of dietary fats and cancer remains unclear.

Does Fiber Prevent Cancer?

The only other dietary factor that can be statistically related to cancer is fruit and vegetable intake. Experts believed this was due to the fiber content of these foods and as a result, much research was conducted to establish this connection. However, like fat, fiber intake alone did not seem to decrease cancer risk in research studies. Rather, the association was with fruit and vegetable intake. Whether that is due to the unique types of fiber found in fruits and vegetables or to some other components in these foods is unknown. Plant foods contain many phytochemicals that are known to be biologically active, and may influence cancer risk in ways no one understands yet. Recent evidence found that lycopene, found in tomatoes, might influence cancer. This resulted in many supplement manufacturers adding small amounts of lycopene to supplements.

Other Inconclusive Dietary Factors

Over the years, there have been countless other dietary and nutritional factors investigated in relation to various cancers. It seems at one point everything enjoyable has been blamed for some type of cancer. Research has since discovered that:

• Coffee consumption does not necessarily lead to cancer
• When consumed in large amounts, grilled meats and alcoholic beverages may create additional risk to some people
• Food additives and pesticides do not clearly create additional risk
• Eating only organic food will not guarantee a cancer-free life.

For more specific dietary components, individual susceptibility, and countless other risk factors, known and unknown, are all part of the cancer risk picture.

Make Healthy Lifestyle Choices

Current knowledge of the link between diet and cancer is insufficient to recommend an anti-cancer diet. At best, recommendations are made to reduce risk by maintaining a healthy weight. This means avoiding weight gain and losing excess weight by cutting calories and increasing physical activity. In addition, the American Cancer Society strongly urges consumption of 5 or more servings of fruits and vegetables daily, and whole grain rather than refined grain foods. In the future, when the genetic components of cancer risk are better understood, it might be possible to recommend cancer prevention diets. But for now, beware of anyone claiming to have a simplistic nutritional answer to this very complex disease.