Diet and cancer

Types of diet

Restrictive diets

It is a popular misconception that cancer can be treated by "starving" a tumour or restricting carbohydrate intake, when in reality the health of people with cancer is best served by following a healthy diet. A number of specific diets and diet-based regimes have been claimed to be useful against cancer, including 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.

Dietary patterns

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.

Unhealthy dietary patterns are associated with a higher body mass index suggesting a potential mediating effect of obesity on cancer risk.

Western pattern diet

Mediterranean diet

Dietary components

Alcohol

Main article: Alcohol and cancer, Alcohol and breast cancer

Alcohol is associated with an increased risk of a number of cancers. It has been reported that 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)."

Eggs

Processed and red meat

There is strong evidence that processed meat and red meat intake increases risk of colorectal cancer. The American Cancer Society in their "Diet and Physical Activity Guideline", stated "evidence that red and processed meats increase cancer risk has existed for decades, and many health organizations recommend limiting or avoiding these foods."

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 and classed them as Group 1 (carcinogenic to humans) and Group 2a (probably carcinogenic to humans) carcinogens respectively. There is some evidence that suggests that heme and nitrite are involved in the processes linking red and processed meat intake with colorectal cancer. Heme is present in particular in red meat and nitrite is used as curing salt in many processed meats.

Processed and unprocessed red meat intake is associated with an increased risk of breast cancer.

The World Health Organization has found that the consumption of processed meat, and potentially red meat, promote carcinogenesis and can increase the risk of colorectal cancer. Colorectal cancer is the second most common cause of cancer death in the world. A 2023 systematic review and meta analysis found that meat consumption was associated with an increased risk of colorectal cancer, colon cancer and rectal cancer. A meta analysis reported in 2024, provided evidence that consumption of high levels of red meat increased the risk of developing esophageal, pancreatic, liver, colon, rectal and colorectal cancers, and that consumption of processed meat (as distinct from red meat) also increased the levels of pancreatic colon, rectal and colorectal cancers. In contrast, high consumption of fish significantly reduced the risk of colon, rectal and colorectal cancers.

A metabolic link has been suggested between a fat- and meat rich diet and cancer associated gut microbes that convert primary bile acids into secondary carcinogenic bile acids.

Salted fish

Fiber, fruits and vegetables

There is strong evidence that consumption of dietary fiber reduces risk of colorectal cancer. Two 2020 meta-analyses found that a high fiber intake was associated with a lower risk of both premenopausal and postmenopausal breast cancers and a higher survival rate in patients with breast cancer.

A 2021 review found that there is moderate-quality evidence 200g of fruit intake per day is associated with a lower risk of breast cancer. Another review found that high total fruit and vegetable consumption are associated with reduced risk of breast cancer. A 2024 review found convincing evidence for high dietary fiber intake associated with lower breast cancer risk.

Pickled vegetables

Flavonoids

Flavonoids (specifically flavonoids such as the catechins) are "the most common group of polyphenolic compounds in the human diet and are found ubiquitously in plants." While some studies have suggested flavonoids may have a role in cancer prevention, others have been inconclusive or suggested they may be harmful.

Methionine

Restriction of methionine has been suggested as a strategy in cancer growth control in cancers that depend on methionine for survival and proliferation. According to a 2012 review, the effect of methionine restriction on cancer has yet to be studied directly in humans and "there is still insufficient knowledge to give reliable nutritional advice".

Reviews of epidemiological studies have found no association between dietary methionine and breast or pancreatic cancer risk.

Mushrooms

According to Cancer Research UK, "there is currently no evidence that any type of mushroom or mushroom extract can prevent or cure cancer", although research into some species continues.

A 2020 review found that higher mushroom consumption is associated with lower risk of breast cancer.

Dairy products

Whole grains

There is strong evidence that consumption of whole grains decreases risk of colorectal cancer.

Saturated fat

Soy

The American Cancer Society have stated that "there is some evidence from human and lab studies that consuming traditional soy foods such as tofu may lower the risk of breast and prostate cancer, but overall the evidence is too limited to draw firm conclusions".

A 2023 review found that soy protein lowers breast cancer risk.

Other

• Green tea consumption has no effect on cancer risk.
• A 2016 meta-analysis showed that women and men who drank coffee had a lower risk of liver cancer.
• A 2014 systematic review found, "no firm evidence that vitamin D supplementation affects cancer occurrence in predominantly elderly community-dwelling women."

References

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