Every day we see reports on medical websites and books that “so-and-so food can prevent cancer and so-and-so diet can keep you away from cancer.” However, as medical practitioners and researchers, we cannot help but question whether these rumors are based on science or not. 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. Therefore it is difficult to verify whether there is really a causal relationship between the two factors in observational studies, but these cohort studies show us the correlation between multiple pairs of factors (e.g., obesity and cancer, diet and cancer, exercise and cancer). In order to prevent cancer, the American Cancer Society (ACS), the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) have jointly recommended several lifestyles for cancer prevention, as follows: (Most of these recommendations have been supported by recent studies) (1) Maintain a normal weight (2) Exercise for at least 30 minutes a day (3) Drink less sugary drinks (4) Avoid (5) Eat more vegetables, fruits, whole grains, and legumes (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) Do not take supplements indiscriminately (9) Eat a low-salt diet The specific findings of the study are as follows: 1. In a clinical trial study of 2905 women at high risk for breast cancer, the risk of breast cancer in this population was reduced by 44% after receiving 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, less alcohol) significantly reduced the risk of breast cancer in women with a BMI <25 kg/m2 by 20% and a BMI=25-29.9 kg/m2 by 30%. The risk of breast cancer was reduced by 30% for women with BMI=25-29.9 kg/m2. 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 development. Excess body fat triggers insulin resistance, and elevated levels of insulin and growth factors promote the development of cancer. Obesity also promotes the production of estrogen, which in turn promotes the development of many cancers, and fat secretes cytokines that promote the development of inflammation. A recent dose-response meta-analysis, which included 50 prospective observational studies, found that maintaining a normal body weight in adults may prevent certain types of cancer, particularly those for which hormone replacement therapy (HRT) is not indicated. In the study, adult women were found to have an 11% increased risk of postmenopausal breast cancer, a 39% increased risk of endometrial cancer, and a 13% increased risk of ovarian cancer for every 5 kg increase in body weight. For every 5 kg increase in body weight in adult men, 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 men. The biggest challenge we face is that adult weight increases with age. Dr. Harvie said, "One of the biggest conundrums is that weight increases with age." 2. Exercise at least 30 minutes a day Several observational studies have found that physical activity can reduce the risk of breast, colorectal and endometrial cancers. A prospective cohort study of U.S. and European populations found that people who exercised at the minimum recommended level of exercise (7.5-15 metabolic equivalents (MET) per week) had a 20% lower risk of cancer death compared 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 cancer studies and 7 colorectal cancer studies with 50,000 patients) found that being physically active reduced the mortality rate of breast and colorectal cancers 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, and legumes In addition to weight control and increased exercise, dietary habits can also influence the occurrence of cancer. A recent meta-analysis of prospective cohort studies of 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 intake of red meat (e.g. beef, pork and lamb) and avoid processed meat products In addition, studies have found that red meat is not as bad as we thought, at least in terms of carcinogenesis. The results of the European Prospective Investigation into Cancer and Nutrition (EPIC), which surveyed 450,000 people, show that the public is concerned about whether processed meat products increase the risk of cancer. One study found that eating an additional 50 g of processed meat products per day increased the risk of cancer by 11%, but the study did not find an association between red meat and cancer risk. Thus, it is processed meat products, not red meat, that should be brought to your attention. 5. Limit the daily intake of alcoholic beverages Heavy alcohol consumption (more than 5 standard drinks per day) is strongly associated with the development of 10 cancers: oropharyngeal cancer (HR, 5.13), esophageal squamous epithelial cancer (HR, 4.95), breast cancer (HR, 1.61), larynx cancer (HR, 2.65), colorectal cancer (HR, 1.44), liver cancer (HR, 2.07), stomach cancer ( HR, 1.2), gallbladder cancer (HR, 2.07), pancreatic cancer (HR, 1.19), and lung cancer (HR, 1.11). Even small amounts of alcohol (1 standard drink per day) can increase the risk of oropharyngeal cancer (HR, 1.17), esophageal squamous epithelial cancer (HR, 1.3) and breast cancer (HR, 1.05). In addition, it cannot be ignored: non-drinking is associated with overall mortality, as there is a trend toward increased cardiovascular morbidity in patients who do not drink alcohol. Not taking vitamin supplements indiscriminately A recent randomized clinical trial examined whether the consumption of vitamin supplements in a healthy population could reduce the risk of cancer. However, the study brought sobering results. Folic acid increased the risk of cancer (HR, 1.07), particularly prostate (HR, 1.24) and colorectal (HR, 1.28) cancers; beta-carotene increased the risk of lung (HR, 1.20) and stomach (HR, 1.54) cancers; selenium increased the risk of non-melanoma skin cancer (HR, 1.44); and vitamin E increased the risk of prostate cancer (HR, 1.17). The risk of prostate cancer (HR, 1.17) was increased by vitamin E. In conclusion, obesity, lack of exercise, and excessive alcohol intake are factors that we should focus on. The evidence on the effect of dietary habits on cancer development is not sufficient, and further in-depth studies are needed to better determine the relationship between them.