By: Ph. D. Lorenzo Cohen: Professor and Director, Integrative Medicine Program at the University of Texas MD Anderson Cancer Center
The American Cancer Society and the American Institute for Cancer Research both estimate that more than 30 percent of cancer can be prevented through healthy diet, physical activity, and maintaining a healthy weight. Smoking also accounts for over 30 percent of cancers. This means that through appropriate lifestyle choices, more than 50 percent of cancers and cancer-related deaths could be avoided.
Diet in and of itself plays an important role in cancer prevention. Though the association between diet and cancer prevention is still not definitive, recent evidence suggests that diet may modify the risk of many cancers, including gastric, colorectal, breast, prostate, and lung cancers. For example, intake of dietary fiber and high consumption of fruit, vegetables, and fish has been associated with reduced risk of a number of cancers. Some population studies also demonstrate that vegetarianism is associated with lower risk of overall cancer and female-specific cancers. On the other hand, red and processed meat, dairy, alcohol, and saturated fat increase the risk of certain cancers.
Research has found that vegetables and fruits containing high level of carotenoids (carrots, sweet potatoes, spinach, kale, papaya, tomatoes, etc.), cruciferous vegetables (cauliflower, cabbage, cress, bok choy, broccoli, etc.), and antioxidant-rich foods (blueberries, blackberries, green tea, garlic, etc.) are linked to lower cancer incidence. Population studies also have suggested that increased plasma level of vitamins A, B, C, E (α-tocopherol), D, and certain types of carotenoids are associated with a decreased risk of cancer. However, the cancer prevention effects of these micronutrients have not been confirmed by a number of large cancer prevention trials including vitamin E and β-carotene for lung cancer (ATBC and CARET trials), Vitamin E, C and β-carotene for prostate cancer (PLCO trial), selenium and vitamin E for prostate cancer prevention (SELECT trial), and folic acid and vitamin B for overall cancer prevention (Norweigian Vitamin Trial). In fact, some trials resulted in an increased incidence of cancer or cancer-related death.
Although it is important to better understand the specific mechanisms within plants that confer health benefits, a purely reductionist approach to isolate specific compounds has not been successful. Whole foods contain a wide array of nutrients including vitamins, minerals, and a number of other biologically active compounds, collectively known as phytonutrients. These phytonutrients, such as 3,3'-diindolylmethane (DIM) in broccoli or isoprenoids and polyphenols in other vegetables, may work in concert to provide the best support for cancer prevention. Recent provocative research demonstrated that plant microRNAs (miRNA acts as a regulator of gene expression) that enter the body in food are present in our body and may influence gene function and ultimately affect our health.
Although more research is needed, there is no doubt that diet plays a role in cancer prevention. Without scientific support for which individual nutrients are most effective in cancer prevention, people should adopt a whole-foods approach to ensure a balanced intake of protective phytonutrients. A diet that is mainly composed of whole grains, a variety of vegetables and fruits, legumes, tea (green and/or black), and nuts and seeds should work synergistically to offer protection against many types of chronic diseases, including cancer.
The old model of cancer as a purely genetic disorder that thrives outside of the patient's control is slowly disappearing. Most scientists and physicians are acknowledging the role of the body's own defenses -- and our lifestyle choices that support them -- in contributing to whether early cancer cells become a life-threatening disease or not. Now is the time for financial investment and scientific efforts that have been dedicated for decades to recruitment into screening programs, chemoprevention, or cancer treatment to be matched with aggressive investments in understanding how lifestyle contributes to cancer risk and in promoting necessary lifestyle changes early after the disease has been detected. As part of true health care reform, we need to focus on teaching children in our schools, employees in our corporations, and physicians in our hospitals how to really increase the odds of preventing and controlling cancer