Several research findings have shown that some foods are associated with an increase or decrease in the risks of certain cancers; however, many of these published data may be biased for several reasons. To reduce such bias, explain data inconsistencies, and establish a consensus, experts merge similar trials about a specific subject and critically analyse them to assess their feasibility per the standard protocols. Such discussions turn into a meta-analysis. It is not astounding to note that 20% of good meta-analyses fail to avoid bias. To further reduce bias among the meta-analyses about foods and cancer risks, Papadimitriou N et al. 2021, conducted an umbrella review of 860 meta-analyses with evidence associating diet and cancer risk.
They noted that alcohol consumption was associated with increased risks of colorectal cancer and breast cancer, whereas calcium, dairy, and whole-grain foods (products) lowered the risk of colorectal cancer. Coffee intake correlated with a reduced risk of liver and skin cancer (basal cell carcinoma). Fruits and vegetable consumption was associated with a reduced risk of head and neck cancers.
They further noted that diet and nutrition might account for 20-25% of the global cancer burden. 10-15% of this burden may be due to obesity due to a high-calorie diet and lack of physical activity. Alcohol may account for another 5%, and other foods like red meat and grains may account for the remaining 5%.
Alcohol alters the oestrogen concentrations within the blood and cells and leads to the proliferation of oestrogen receptors within the mammary epithelial cells. The receptors enhance the risk of breast cancer.
Chronic alcohol intake creates an imbalance of intestinal bacteria, dysregulates the permeability of the luminal cells, and increases oxidative stress. These changes increase the risk of colorectal cancer, alcoholic liver disease, and liver cancer. When alcohol reaches the liver, the enzymes metabolise it to acetaldehyde and other products. Acetaldehyde is toxic to several cells. Its interaction with the DNA can create mutations that may lead to the development of cancers.
The observation that calcium and dairy products reduce the risks of colorectal cancer might be because calcium forms insoluble soaps within the colon as it binds to various free fatty acids and bile salts that could promote colonic tumours. They might also preserve intestinal luminal cell integrity and maintain a robust immune response within the intestines. They further noted that lactic acid bacteria absorb toxins from cooked foods that could potentiate cancer development. The bacteria also reduce inflammation within the intestines.
Because whole-grain foods contain dietary fibre, they reduce transit time during food digestion, dilute contents within the colon, and enhance intestinal bacteria food breakdown. The reduced transit time curtails the epithelial cells contact with toxins within the food that could cause cancer. Another observation was that whole-grain foods reduce fasting insulin concentrations. Elevated fasting insulin levels are highly associated with colorectal cancer.
Coffee contains abundant antioxidants. They curb oxidative stress and inflammatory tendencies that could result in the development of cancers. It lowers the risks of liver cancer by possibly reducing a surge in the markers of liver injury.
In a nutshell, most of these foods must be in moderate quantities. No good prevails in consuming alcohol. Common sense is crucial. You can read the full paper by visiting nature via this link.