Nutrition, Diet, and Anti-aging: Cancer Prevention and Nutrition/Diet

While the concept of evidence-based medicine is well-established, prevention also needs to be based on evidence. When health care professionals intervene in the unique culture and preferences of individuals and ethnic groups in the name of dietary guidance, there is a need for solid evidence that the probability of getting cancer decreases in return for implementing it. Simply stating that “it has antioxidant effects” or “it suppressed cancer development in mice” is insufficient as evidence. The most reliable evidence comes from intervention studies with random allocation (randomized controlled trials). However, when the incidence of cancer is the endpoint, large-scale long-term studies under strict control are necessary, and the number of studies is limited, so there is not much evidence available. So far, antioxidant nutrients such as β-carotene, vitamin E, and vitamin C have not shown the expected cancer prevention effects theoretically, and it has been shown that high doses of β-carotene and vitamin E increase the risk of certain cancers and cerebrovascular diseases. Also, it has been clearly shown that reducing the intake of fat (fat energy ratio) in adulthood does not prevent breast cancer or colorectal cancer. The next most reliable evidence is provided by cohort studies. This is an observational study that sets up a large target group, first understands factors such as dietary habits through questionnaires, and then tracks the occurrence of cancer over a long period. It is less likely to be biased and relatively reliable. However, there is a limitation that the relationship seen between a factor and cancer incidence may actually be due to a third factor (confounding factor), and the research results may be apparent. When developing cancer prevention methods based mainly on cohort studies, it is necessary to have backing for the mechanism through experiments in animals or in test tubes. In addition, evidence from research methods such as case-control studies and cross-sectional studies can be used, but while they can be conducted in a relatively short time and at low cost, biases and reversals of causality from the time axis are likely to occur. Regardless of the type of research method, the relationship obtained in a single study cannot deny the possibility of chance, bias, and confounding, so it is necessary to evaluate the presence or absence of a causal relationship based on multiple studies.