Cancer Prevention DietIt is widely agreed that appropriate dietary habits decrease the risk of cancer. The same diet recommended to the general population to prevent cancer is also recommended for cancer patients to follow during and after treatment in order to contribute toward disease control and minimize recurrence. The following basic recommendations are stressed by numerous citations in the bibliography, including American Institute for Cancer Research (2002a, 2002b), Goodman (2001), Keane and Chace (1996), Murray et al (2002), Nixon (2000), and World Cancer Research Fund / American Institute for Cancer Research (1997).
1. Include lots of different fruits and vegetables and whole grains and legumes (beans) in your diet. Eat at least 5 servings of fruits and vegetables per day and 7 servings of whole-grain foods, legumes, and nuts. This single recommendation is the most important for accomplishing two goals. First, it provides vitamins, minerals, and other micronutrients, plus non-nutrients with possible anti-cancer effects such as phytochemicals (flavonoids, isoflavones, lignans, polyphenols, and others). These healthy whole foods include antioxidants which can counteract carcinogenic effects at the cellular level by combatting free radicals. Free radicals are unstable molecules (usually containing oxygen or nitrogen) which can damage normal cells and their DNA through chemical reactions. Antioxidants stabilize these molecules, thereby preventing cell damage; this may slow or prevent the development of cancer. Second, this plant-based diet provides fiber (roughage) for colon health.
2. Limit red meat consumption. Three ounces of red meat per day is the maximum recommended by WCRF/AICR, but other authors recommend eating red meat only occasionally. Choose fish, chicken, legumes, soy-based foods, eggs, and low-fat dairy products as your main protein sources. It is important to get enough protein. Some sources (Deane and Chace, 1996; Martin, 2000) indicate that cancer survivors require greater amounts of protein than typical persons: 1-1.5 grams of dietary protein per kilogram of body weight per day, compared to 0.8-1.0 g/kg/day for the general population.
3. Reduce fat consumption to 20-30% of calorie intake. Avoid fats of animal origin and hydrogenated fats in cooking and in purchased baked products. Avoid polyunsaturated cooking oils such as corn, safflower, and sunflower oils; these contain omega-6 fatty acids. Avoid baked goods and crackers containing trans-fats. Choose olive oil and canola oil (rapeseed oil) for cooking. Omega-3 fatty acids are healthy and desirable. Omega-3 fatty acids are found in certain fish (such as sardines, salmon, mackerel, albacore tuna), walnuts, and golden flaxseed (which can be ground in a coffee grinder and added to other foods).
4. Restrict intake of salt, including salty and salt-cured foods, table salt, and salt used in cooking.
5. If you drink alcohol, consume no more than two alcoholic drinks per day for men, one for women.
6. Do not eat charred food. A substance called IQ (which stands for A2-amino-3-methylimidazo[4,5-f] quinolone@) has been identified as “reasonably expected to be a human carcinogen” (NIEHS, 2003). IQ forms when meat or eggs are cooked in direct high heat. Restrict food grilled in direct flame to occasional consumption, and cook meats using lower-temperature methods rather than high-temperature methods such as broiling. Limit intake of smoked or cured meats (hot dogs, bacon, etc.).
7. Avoid being overweight, and do exercise on a daily basis.
SPECIFIC RECOMMENDED FOODS
Consistent with the general cancer prevention diet discussed above, specific foods may be particularly health-promoting. For example, brassica or cruciferous vegetables (the cabbage family, including bok choi, broccoli, brussels sprouts, cabbage, cauliflour, collards, kale, and mustard greens) are especially rich in antioxidants and are associated with reduced cancer incidence in epidemiological studies (Van Poppel et al, 1999). There has been discussion in the literature of the benefits of drinking green and black teas for their polyphenol content.
Some authors urge cancer survivors to use particular foods. Whey protein powder is recommended as enabling the body to make and use glutathione and glutamine for normal cells, while simultaneously depleting glutathione in cancer cells, thereby inhibiting their growth and making them more susceptible to cancer treatments (Moss, 2000; Murray et al, 2002). Boik (2001) and Roth et al (2002) provide additional support for the importance of glutamine and glutathione metabolism.
Probiotic foods replenish the populations of helpful bacteria in the gut. The most familiar example is the lactobacillus culture that turns milk into yogurt. Murray et al (2002) recommend not only probiotic foods such as yogurt but also proteolytic enzyme supplements to assist in digestion, enhance immune response, inhibit tumor angiogenesis and metastasis, and promote differentiation of cancer cells. Boik (2001) also discusses the potential anti-cancer properties of bromelain, a proteolytic enzyme.
Scientists are regularly identifying new substances within whole foods which have beneficial properties; in other words, we don=t yet know everything that makes food good for us. Supplements are available to enable us to increase our intake of some previously identified substances, but it is still necessary to eat good whole foods in order to get the wide variety of micronutrients, non-nutritive substances, and unidentified beneficial substances in combinations which only foods provide. That is, no one should expect to eat junk food plus supplements and stay healthy. However, vitamin and mineral supplements can provide both insurance of adequate nutrient intake and an extra source of desirable nutrients.
In the United States of America, minimum intakes of vitamins and minerals are established by the Food and Nutrition Board of the Institute of Medicine, part of the National Academy of Sciences (see references). The Board establishes Recommended Dietary Allowances (RDAs) for selected nutrients based on the minimum amount needed to prevent deficiency diseases such as rickets or scurvy. The Board has also established Tolerable Upper Intake limits for a few nutrients to prevent diseases or disorders associated with excess intake. Note that these Tolerable Upper Intakes are set very low so as to prevent any adverse effects for the most susceptible individuals who have particular health problems that could be aggravated by the vitamin in question. However, the Board has not established desirable intake levels for optimum health.
Fat-soluble vitamins (A, E, D, and K) can be stored in body fat; therefore, avoid taking excess amounts to prevent adverse effects of accumulation in body tissues. Water-soluble vitamins (C and the B vitamin group) do not accumulate in tissue; excess amounts beyond daily use are excreted. In contrast to vitamins and minerals, daily intakes for many nutrients and non-nutrient substances have not yet been established.
Shown in Table 1 are the RDA and Tolerable Upper Intake values (when available) for vitamins and minerals, plus additional columns showing the recommended intakes for cancer survivors as suggested by several different nutrition authors. Click the link below to view the table as a pdf.
TABLE 1. Recommend Dietary Allowances and tolerable upper intake levels (when available) from the Food and Nutrition Board of the Institute of Medicine, compared to recommendations for cancer survivors by the referenced authors.
You will note in Table 1 that there are differences of opinion regarding the optimal intakes among the sources represented by the columns. The individual authors writing for cancer survivors generally recommend intakes above and beyond the RDAs, sometimes above the Tolerable Upper Intake Levels. In contrast, medical and nutritional professional associations generally recommend only supplements not exceeding 100-200% of the RDA values (minimum intakes to prevent deficiencies). Seifried et al (2003) and Norman et al (2003) summarize some concerns about use of antioxidant supplements by cancer survivors; essentially the scientific evidence is not conclusive or consistent enough to support recommending supplements, and there is inadequate understanding of the relationships among the factors which affect the results. More research is needed. One concern about supplements does not apply to GIST patients taking Gleevec: there is controversy about whether antioxidant supplements could interfere with some types of chemotherapy and radiation therapy for cancer, but there is no suggestion that this might apply to Gleevec.
In evaluating these conflicting opinions, it is important to understand that medical groups generally make recommendations only after there is sufficient scientific evidence available to meet their criteria for conclusive evidence. They prefer to make recommendations upon the basis of prospective randomized double-blind clinical trials using large numbers of subjects over long time periods. For example, a study was recently initiated which will recruit over 30,000 men to receive either two placebos, or selenium plus one placebo, or vitamin E plus one placebo, or selenium plus vitamin E, over a period of 12 years, after which effects on prostate and other cancers will be assessed (the ASELECT@ study described on the website of the National Cancer Institute). For a description of the criteria used by the National Cancer Institute for evaluating human clinical cancer research, see the ALevels of Evidence for Human Studies of Cancer@ document posted on their website.
Because this type of research is expensive and time-consuming, there are few such studies; therefore, recommendations from groups of experts are slow in coming. Furthermore, for-profit companies will not undertake research on substances for which they cannot obtain patents. Therefore, cancer survivors may need to make their own assessments of the potential benefits and risks of dietary supplements, as well as other nutrients. Information available from government websites such as the Food and Nutrition Information Center, National Agricultural Library of the US Department of Agriculture can be helpful in assessing nutritional supplements.
In addition to vitamins and minerals, many herbal and other supplements are marketed. There is abundant evidence in animal studies and in vitro (test-tube) studies of human cancer cell lines that natural plant-derived chemicals can slow the growth of cancer. One detailed summary of the cellular mechanisms of action of such substances, as well as relevant research regarding their use, is Natural Compounds in Cancer Therapy by Boik (2001). However, there are also many substances on the market for which there are little if any health benefits. To assess potential benefit, consumers can consult websites such as the Office of Dietary Supplements at the National Institutes of Health (NIH), the National Center for Complementary and Alternative Medicine at NIH, and Quackwatch.
American Dietetic Association
American Institute for Cancer Research
Food and Nutrition Board, Institute of Medicine, National Academy Press.
Food and Nutrition Information Center, National Agricultural Library, USDA
National Cancer Institute
National Center for Complementary and Alternative Medicine, NIH
Office of Dietary Supplements, National Institutes of Health (NIH)
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A GUIDE TO ABBREVIATIONS AND MEASUREMENTS USED IN TABLE 1 AND OTHER CONVERSION FACTORS
1 gram (g) = 1000 milligrams (mg) = 1,000,000 micrograms (mcg or g).
Most vitamins are measured in milligrams or micrograms.
Vitamins A, D and E are also measured in International Units, or IUs, a measurement designed to standardize the different forms of these vitamins that have different potencies. Note! The conversion between the metric system (mg, mcg, etc.) and IUs varies from vitamin to vitamin.
1 mcg of retinol (mcg RE) = 3.3 IU of vitamin A
100 IU of vitamin D = 2.5 mcg.
100 IU of vitamin E = 67 mg.
1 mcg of retinol = 6 mcg of beta-carotene
1 pound (lb) = 16 ounces (oz)
2.2 lb = 1 kilogram (kg)
1 pint = .57 liters
1.76 pints = 1 liter
One must be careful and always, always read the fine print. In some books and printed food content labels the word calories (It should be a capital C) actually means kilocalories (kcal). It is unfortunate, but worldwide standards of definitions of terms as well as quantities do not seem to be in place when it comes to labeling vitamins and supplements. So read the fine print.
M - male, F - female