We often see reports like “XX foods can prevent cancer” and “YY diet can keep you away from cancer” on medical websites and books. However, as medical practitioners and researchers, we cannot help but ask whether there is any scientific basis for these rumors. Professor Michelle Harvie from the University of South Manchester, UK, pointed out at the 2015 ASCO Annual Conference that most of the current cancer prevention recommendations come from observational studies rather than randomized trial results. Although it is difficult to verify whether there is really a causal relationship between two factors in observational studies, this presents us with correlations between multiple pairs of factors, such as obesity and cancer, diet and cancer, and exercise and cancer. The American Cancer Society (ACS), the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) have issued a joint article recommending a lifestyle for cancer prevention, specifically the following five points. Maintaining a normal weight with a BMI <25 kg/m2 reduces the risk of breast cancer in women This recommendation is not listed by the three departments out of thin air, but is based on the results of several recent randomized clinical trials. To prevent breast cancer, the ACS recommends that women get at least 150 minutes of moderate-intensity exercise per week, drink up to one standard drink of alcoholic beverages per day, and maintain a body mass index (BMI) of less than 25 kg/m2. In one clinical trial (2905 women), women at high risk of developing breast cancer had a 44% reduction in their risk of developing the disease after following the ACS recommendations. The Women's Health Initiative Watch (64,000 women) study found that a healthy diet (more fruits and vegetables, less meat, less alcoholic beverages) significantly reduced the risk of breast cancer in women, for example by 20% for women with a BMI <25 kg/m2 and 30% for women with a BMI=25-29.9 kg/m2. It is important to note that a healthy diet does not reduce the risk of breast cancer in obese women. You may not be surprised to hear this, as BMI is a cancer risk factor in its own right. Excess body fat triggers insulin resistance, and elevated levels of insulin and growth factors can promote cancer development. Obesity also promotes the production of estrogen, which in turn is a stimulant for many cancers. In addition, fat secretes cytokines that promote inflammation. A recent dose-response meta-analysis (involving 50 prospective observational studies) found that maintaining a normal weight in adults may prevent certain types of cancer, particularly those not amenable to hormone replacement therapy (HRT). For example, for every 5 kg increase in body weight in adult women, the relative risk of postmenopausal breast cancer increased by 11%, postmenopausal endometrial cancer by 39%, and postmenopausal ovarian cancer by 13%. The key problem is that the weight of adults increases with age, and this cannot be prevented. So you can only manage your health well. Increased physical activity MET=7.5-15, reduced risk of cancer death Several observational studies have found that physical activity can reduce the risk of breast, colorectal and endometrial cancers. A study of U.S. and European populations found that those who exercised at the minimum recommended level of exercise - a metabolic equivalent (MET) of 7.5-15 per week - had a 20 percent lower risk of cancer death compared to those who were physically inactive. At the 2015 ASCO Annual Meeting, Professor Donald Abrams of the University of California noted that exercise can improve outcomes for patients with diagnosed cancer. A recent meta-analysis of breast and colorectal cancer survivors (50,000 patients) found that active exercise reduced breast cancer mortality and colorectal cancer mortality among survivors. This shows that it is more important for cancer patients to adopt these cancer prevention recommendations after receiving treatment. Eat more vegetables, less meat In addition to weight control and increased exercise, dietary habits can also influence cancer. A recent meta-analysis study found that eating more vegetables and fruits reduced all-cause mortality and cardiovascular mortality in people, but was not associated with cancer-related mortality. In addition, the study found that lean meat is not as bad as we might think, at least from a cancer risk perspective. The results of the European Prospective Investigation into Cancer and Nutrition (EPIC) showed that a major concern was whether processed meat products increased the risk of cancer. One study found that eating an additional 50 g of processed meat products per day was associated with an 11% increased risk of cancer. However, lean meat was not associated with cancer risk. This shows that processed meat products are more important to be aware of than lean meats. Moderate alcohol consumption 1 standard glass of alcohol per day and no more Heavy alcohol consumption (more than 5 standard glasses of alcohol per day) is significantly associated with the development of 10 cancers: oropharyngeal cancer, esophageal squamous epithelial cancer, breast cancer, laryngeal cancer, colorectal cancer, liver cancer, stomach cancer, gallbladder cancer, pancreatic cancer, and lung cancer. In addition, studies have found that small amounts of alcohol (1 standard glass of alcohol per day) can increase the risk of oropharyngeal, esophageal squamous epithelial, and breast cancers. However, recent studies have reported that moderate alcohol consumption can prevent cancer. In addition, it is important not to lose sight of the fact that abstaining from alcohol is associated with higher overall mortality, as there is a trend toward higher cardiovascular morbidity among non-drinkers, so we cannot simply advocate that "abstaining from alcohol is healthy. Don't take vitamin supplements if you're not deficient A recent randomized clinical trial examined whether vitamin supplements could reduce the risk of cancer in a healthy population. However, the study brought about sobering results. For example, folic acid increased the risk of cancer, especially prostate and colorectal cancers; beta-carotene increased the risk of lung and stomach cancers; selenium increased the risk of non-melanoma skin cancer; and vitamin E increased the risk of prostate cancer. In summary, obesity, lack of exercise, and excessive alcohol intake are risk factors for cancer development and should be given significant attention. However, the evidence that dietary habits affect cancer is not conclusive, and the relationship between the two needs to be studied in depth.