Every day we can see reports on medical websites and books that “so-and-so food can prevent cancer, so-and-so diet can keep you away from cancer.” However, as medical practitioners and researchers, we can’t help but question whether these rumors have any scientific basis. Professor Michelle Harvie from the University of South Manchester, UK, pointed out at the 2015 ASCO Annual Meeting that most of the current recommendations for cancer prevention come from observational studies, not from randomized trials. It is therefore difficult to verify whether there is really a causal relationship between two factors in observational studies, but these cohort studies show us correlations between multiple pairs of factors (e.g. obesity and cancer, diet and cancer, exercise and cancer). In order to prevent cancer, the three major departments of the American Cancer Society (ACS), the World Cancer Research Fund (WCRF), and the American Institute for Cancer Research (AICR) have joined together to recommend several lifestyles for preventing cancer as follows: (1) Maintaining a normal weight (2) Exercising for at least 30 minutes a day (3) Drinking fewer sugary beverages (4) Avoiding high-calorie diets (5) Eating more vegetables, fruits, and whole grains, (6) Limit intake of red meat (e.g., beef, pork, and lamb) and avoid processed meat products (7) Limit daily intake of alcoholic beverages (8) Don’t take supplements indiscriminately (9) Eat a low-salt diet Specific findings of the study are as follows: 1. Maintain a normal body weight In order to prevent breast cancer, the ACS recommends that women engage in moderate-intensity physical activity for at least 150 minutes per week, consume up to one alcoholic beverage per day, and maintain BMI. To prevent breast cancer, the ACS recommends that women engage in at least 150 minutes of moderate-intensity physical activity per week, consume at most one alcoholic beverage per day, and maintain a BMI of less than 25 kg/m2 In a clinical trial study that included 2,905 women at high risk for breast cancer, the risk of breast cancer in this population was reduced by 44% after receiving the ACS recommendations. The Women’s Health Initiative Observational Study, which included 64,000 women, found that a healthy diet (more vegetables and fruits, less meat, and less alcoholic beverages) significantly reduced the risk of breast cancer by 20% in women with a BMI of <25 kg/m2 and by 30% in women with a BMI of 25-29.9 kg/m2. Women with a BMI of 25-29.9 kg/m2 had a 30% lower risk of breast cancer. However, it is important to note that a healthy diet does not reduce the risk of breast cancer in obese women. This is because BMI itself is a risk factor for cancer. Excess body fat triggers insulin resistance, and elevated levels of insulin and growth factors promote cancer. Obesity also promotes the production of estrogen, which in turn promotes the development of many cancers, and fat secretes cytokines that promote inflammation. A recent dose/response meta-analysis of 50 prospective observational studies found that maintaining a normal body weight in adults may prevent certain specific types of cancer, especially those for which hormone replacement therapy (HRT) is not indicated. The study found that for every 5 kg of weight gain in adult women, there was an 11% increase in the risk of postmenopausal breast cancer, a 39% increase in the risk of endometrial cancer, and a 13% increase in the risk of ovarian cancer. For every 5 kg of weight gain in adult males, the risk of colon cancer increases by 9%, and the risk of kidney cancer is 1.42 times higher than that of normal-weight adult males. The biggest dilemma we face is that adult weight increases with age. Dr. Harvie said, "One of the biggest dilemmas is that weight increases with age." 2, Exercise at least 30 minutes a day Several observational studies have found that physical activity reduces the risk of breast, colorectal, and endometrial cancer. A prospective cohort study of U.S. and European populations found that those who exercised to the minimum recommended level of exercise (7.5-15 metabolic equivalents per week (MET)) had a 20 percent lower risk of cancer death relative to those who lacked exercise. At the 2015 ASCO Annual Meeting, Professor Donald Abrams of the University of California noted that exercise improves the prognosis of cancer patients. A recent meta-analysis of breast and colorectal cancer survivors (16 breast and 7 colorectal cancer studies with 50,000 patients) found that being physically active reduced breast and colorectal cancer mortality in survivors. Therefore, it is even more important for cancer patients to adopt these cancer prevention recommendations after receiving treatment. 3. Eat More Vegetables, Fruits, Whole Grains, Beans and Other Foods In addition to controlling body weight and increasing exercise, dietary habits can also affect the occurrence of cancer. A recent meta-analysis of prospective cohort studies that included nearly 1 million people found that eating more fruits and vegetables reduced all-cause mortality and cardiovascular mortality, but was not associated with cancer-related mortality. 4. Limit your intake of red meat (such as beef, pork and lamb) and avoid processed meat products Additionally, studies have found that red meat isn't as bad as we thought it was, at least when it comes to causing cancer. The results of the European Prospective Investigation into Cancer and Nutrition (EPIC), which surveyed 450,000 people, showed that the public's concern is whether processed meat products elevate the risk of cancer. A study found that an additional 50 g of processed meat products per day would increase the risk of cancer by 11%, but the study did not find that red meat was associated with the risk of cancer. This shows that it is processed meat products, not red meat, that should attract attention. Limiting daily intake of alcoholic beverages Heavy alcohol abuse (drinking more than 5 standard drinks per day) is strongly associated with the development of 10 types of cancer: oropharyngeal cancer (HR, 5.13), esophageal squamous epithelial cancer (HR, 4.95), breast cancer (HR, 1.61), laryngeal cancer (HR, 2.65), colorectal cancer (HR, 1.44), liver cancer (HR, 2.07), stomach cancer (HR, 1.2), biliary tract cancer (HR, 1.5), and other cancers. (HR, 1.2), gallbladder (HR, 2.07), pancreas (HR, 1.19), and lung (HR, 1.11). Even small amounts of alcohol (1 standard drink per day) increase the risk of oropharyngeal cancer (HR, 1.17), squamous epithelial cancer of the esophagus (HR, 1.3) and breast cancer (HR, 1.05). In addition, it should not be overlooked that non-drinking is associated with overall mortality, as there is a tendency for cardiovascular morbidity to be elevated in non-drinking patients. A recent randomized clinical trial examined whether the consumption of vitamin supplements in healthy populations could reduce the risk of cancer. However, the study brought sobering results. Folic acid was associated with an increased risk of cancer (HR, 1.07), particularly prostate cancer (HR, 1.24) and colorectal cancer (HR, 1.28); β-carotene was associated with an increased risk of lung cancer (HR, 1.20) and gastric cancer (HR, 1.54); selenium was associated with an increased risk of non-melanoma skin cancer (HR, 1.44); and vitamin E was associated with an increased risk of prostate cancer (HR, 1.44). Vitamin E increases the risk of prostate cancer (HR, 1.17). In summary, obesity, lack of exercise, and excessive alcohol intake are factors that should be emphasized. However, the evidence on the effect of dietary habits on cancer development is not sufficient, and further studies are needed to better characterize the relationship between the two.