Diet and cancer

Dr Kirti Bushan
Nutrition is the science of food and its relationship to health. Diet is a double edge sword. On one end, its consumption, breakdown in body and utilisation as a fuel by body is essential for body’s growth and activity; on the other hand it is linked in etiology of cancers. The association between diet and the risk of cancer has been the subject of debate in a number of epidemiologic studies because to pinpoint dietary carcinogen as main cause in the background of many confounding variables (e.g, lifestyle, alcohol, smoking, physical activity, body weight) is very difficult. The studies have taken various diet assessment instruments and variables into account to establish any bearing of diet on cancer. These include dietary habits, constituents, food frequency questionnaire, 7 day diet record , total intake in 24 hrs, quality of food intake, dietary fat consumption, alcohol & cigarette intake and total energy intake. About 67%, i.e, 2 in 3 cases are linked to diet. Diet modifications lead to prevention of cancers.
The dietary carcinogens are classified into 4 main types – Naturally occurring, during preparation of food, synthetic carcinogens and procarcinogens. The naturally occurring dietary carcinogens include pesticides and mycotoxins (aflatoxins B1). The dietary carcinogens formed during food preparation include heterocyclic aromatic amines (HAA), polycyclic aromatic hydrocarbons (PAH), nitrosamines, urethane, acrylamide. The synthetic carcinogens include directly acting (intentional) and indirect acting (unintentional) carcinogens. It includes artificial sweetners, food and colouring materials, flavouring agents, antioxidants, solvents, vinyl chloride, humefactants. Procarcinogens are dietary components which are converted in body to carcinogens.
The interaction of dietary carcinogens with cellular DNA is known as nutrigenomics. It can lead to carcinogenesis by variety of mechanisms which include – altered cell cycle, activation of oncogenes, tumor suppressor gene inactivation, DNA breaks and faulty DNA repairs, inhibiting apoptosis (cell death), hormonal or antihormonal effects.
The most important impact of diet on the risk of cancer is mediated through body weight . Overweight, obesity and inactivity are major contributors to cancer risk. Obese individuals have substantially higher risk for all cancers and in particular for colorectal cancers, postmenopausal breast cancers, uterine cancers. Weight gain of 10kgs or more is associated with significant increase in postmenopausal breast cancer incidence among women who never use hormonal replacement therapy while weight loss of comparable magnitude after menopause substantially decrease breast cancer risk. Regular physical activity contributes to a lower prevalence of overweight and obesity and consequently reduces the burden of cancer through this pathway.
Alcohol has been classified as carcinogen by IARC. Its consumption increases risk of various cancers including liver, esophagus, pharynx, oral cavity, larynx, breast and colorectum in a dose dependant fashion. Mechanism of alcohol carcinogenesis include direct damage to cells, modulation of DNA methylation, increase in acetaldehyde (main metabolite of alcohol) which forms DNA adducts and enhances proliferation of epithelial cells, interaction with folates (endogenous) leading to decrease in folate and other antioxidants.
A strong association has been seen with dietary fat and cancers of breast, colon, prostate and endometrium. The correlation is strong with animal fat but not vegetable fat. The breast cancer risk increases with increased animal fat intake especially in post menopausal females. The possible reason being obesity with increased body mass index, increased estrogen levels. In colorectal cancers increase in fat intake increases bile acid secretion in intestines containing apcholic acid which is carcinogenic; animal fat also increases low density lipoproteins (LDL) required by tumor cells to grow.
Cooked meat (red meat) leads to increased heterocyclic aromatic amines (HAA) in diet due to pyrolysis and causes carcinogenesis. Decreased intake of dietary fibers, fruits and vegetables, antioxidants (selenium),vitamins, folates and methionine in diet all lead to increased risk of cancer. Increased intake of Vit D, selenium, calcium, tomatoes (lycopene) & soy have been shown to decrease risk of prostate cancer.
These are plant polysaccharides and lignins resistant to hydrolysis by the digestive enzymes. Dietary fibers are soluble and insoluble fibers. Soluble fibers include starch, pectin, gums, some hemicelluloses and other polysaccharides. Source of soluble fibers are fruits, vegetables, bean, barley, oats, bran. Insoluble fibers are lignins, cellulose, most hemicelluloses. The source of insoluble fibers include whole wheat, cereals, beans, skin of fruits and vegetables. The dietary fibers act as anticancer agent in colorectal cancers by following mechanisms:-Fibers cause bulking effect and decrease colonic transit time so less exposure to luminal carcinogens; dilutes bile acid carcinogens; may induce apoptosis; contain phytates which inhibit colonic calcium absorption; cause concurrent decrease fat & decrease calorie intake causing decreased weight again ; and fibers produce short chain fatty acids which are not harmful.
Recommendation for a proper anticancer diet include:-
* Total calorie requirement 40k/cal/kg/day.
* Carbohydrate in diet should contribute 50-70% of calories.
* Proteins should be 15-20% of total calories.
* Fats should contribute 20-30% of total calories.
* Avoid animal fats.
* Vegetable fat favoured (mono unsaturated fat).
* Avoid hydrogenated fats.
* Omega 3 fatty acid favoured.
* Dietary cholesterol should be < 300mg/day
* Dietary fibers intake should be more (25gm/day).
* Eat a lot of raw fruits and vegetables.
* Switch over from animal based to plant based food.
* Eat more soy products.
* Oil rich in omega 3 fatty acid, mono saturated fats favoured (e.g, olive oil).
* Avoid saturated and hydrogenated oil.
* Calcium rich food preferred – for < 50 years age – 1000 ?g/day; for > 50 years age – 1200 ?g/day. Calcium binds bile acids and decreases risk of colorectal cancers.
* Drink less alcohol. Beer contains nitroamines, Red wine contains tannins and grape wine phytonutrients. Dose limitations are canes of beer or 2 small glasses of wine or 2 average cocktails per day. One drink per day for females and 2 drinks for males may serve as a physiologic limit for intake.
* Eat more vitamins and minerals. Vitamin A, B, C, D and minerals & trace elements like Copper, Zinc, Iron, Potassium, Magnesium, should be sufficient in diet.
* For normal bacterial flora in intestine acidophilas powder preffered.
* Fish liver oil, garlic, green tea preferred.
* Salt and sodium restriction (< 6gm/day).
* Body Mass Index (BMI) should be restricted to 27 kg/m2 in males and 25 kg/m2 in females.
* Eat more antioxidants in diet. It includes – Vitamin E, Selenium, ? carotene, Lycopene.
* TOP ANTICANCER VEGETABLES preferred. These are – Broccoli, Brussel sprout, cabbage, carrots, cauliflower, green beans, soy, sweet potato, tomato, pepper, raddish.
* TOP ANTICANCER FRUITS are Apricot, blue berries, grape fruits, lemon, oranges, mangoes, papaya, peaches and strawberries.
(The author is consultant surgical oncologist at Asian Institute of Oncology, SL Raheja(Fortis) hospital, Lilavati hospital, Mumbai)