Diet and cancer

Dietary factors are recognized as having a significant effect on the risk of cancers, with different dietary elements both increasing and reducing risk. Diet and obesity may be related to up to 30-35% of cancer deaths, while physical inactivity appears to be related to 7% risk of cancer occurrence. One review in 2011 suggested that total caloric intake influences cancer incidence and possibly progression. Dietary factors are recognized as having a significant effect on the risk of cancers, with different dietary elements both increasing and reducing risk. Diet and obesity may be related to up to 30-35% of cancer deaths, while physical inactivity appears to be related to 7% risk of cancer occurrence. One review in 2011 suggested that total caloric intake influences cancer incidence and possibly progression. While many dietary recommendations have been proposed to reduce the risk of cancer, few have significant supporting scientific evidence. Obesity and drinking alcohol have been correlated with the incidence and progression of some cancers. Lowering the drinking of beverages sweetened with sugar is recommended as a measure to address obesity. A diet low in fruits and vegetables and high in red meat has been implicated but not confirmed, and the effect may be small for well-nourished people who maintain a healthy weight. Some specific foods are linked to specific cancers. Studies have linked eating red or processed meat to an increased risk of breast cancer, colon cancer, prostate cancer, and pancreatic cancer, which may be partially explained by the presence of carcinogens in foods cooked at high temperatures. Aflatoxin B1, a frequent food contaminate, causes liver cancer, but drinking coffee is associated with a reduced risk. Betel nut chewing causes oral cancer. Pickled vegetables are directly linked to increased risks of several cancers. The differences in dietary practices may partly explain differences in cancer incidence in different countries. For example, stomach cancer is more common in Japan due to its high-salt diet and colon cancer is more common in the United States. Immigrant communities tend to develop the risk of their new country, often within one generation, suggesting a substantial link between diet and cancer. Dietary recommendations for cancer prevention typically include weight management and eating 'mainly vegetables, fruit, whole grains and fish, and a reduced intake of red meat, animal fat, and refined sugar.' A number of diets and diet-based regimes are claimed to be useful against cancer. Popular types of 'anti-cancer' diets include the Breuss diet, Gerson therapy, the Budwig protocol and the macrobiotic diet. None of these diets has been found to be effective, and some of them have been found to be harmful. Nutritional epidemiologists use multivariate statistics, such as principal components analysis and factor analysis, to measure how patterns of dietary behavior influence the risk of developing cancer. (The most well-studied dietary pattern is the mediterranean diet.) Based on their dietary pattern score, epidemiologists categorize people into quantiles. To estimate the influence of dietary behavior on risk of cancer, they measure the association between quantiles and the distribution of cancer prevalence (in case-control studies) and cancer incidence (in longitudinal studies). They usually include other variables in their statistical model to account for the other differences between people with and without cancer (confounders). For breast cancer, there is a replicated trend for women with a more 'prudent or healthy' diet, i.e. higher in fruits and vegetables, to have a lower risk of cancer. A 'drinker dietary pattern' is also associated with higher breast cancer risk, while the association is inconsistent between a more westernized diet and elevated risk of breast cancer. Pickled foods are linked with cancer. Alcohol is associated with an increased risk of a number of cancers. 3.6% of all cancer cases and 3.5% of cancer deaths worldwide are attributable to drinking of alcohol. Breast cancer in women is linked with alcohol intake. Alcohol also increases the risk of cancers of the mouth, esophagus, pharynx and larynx, colorectal cancer, liver cancer, stomach and ovaries. The International Agency for Research on Cancer (Centre International de Recherche sur le Cancer) of the World Health Organization has classified alcohol as a Group 1 carcinogen. Its evaluation states, 'There is sufficient evidence for the carcinogenicity of alcoholic beverages in humans. …Alcoholic beverages are carcinogenic to humans (Group 1).' On October 26, 2015, the International Agency for Research on Cancer of the World Health Organization reported that eating processed meat (e.g., bacon, ham, hot dogs, sausages) or red meat was linked to some cancers. The evidence on the effect of dietary fiber on the risk of colon cancer is mixed with some types of evidence showing a benefit and others not. While eating fruit and vegetables has a benefit, it has less benefit on reducing cancer than once thought.