We are what we eat. Diet plays an important role in supporting our body function. To extend it far, diet is sure to have something to do with cancer incidence. In consideration of cancer ranking as the top cause of death worldwide, it is of significance to know the relationship between diet and cancer risk.
In the past decades, many researchers investigated the association between diet and cancer risk. Though many studies indicate the positive effects of diet on cancer risk, it is still difficult to determine the exact effect of diet on cancer risk due to multiple determinants involved in the clinical experiments.
A collaborative research team composing of researchers from the UK, New Zealand, USA, and Japan published a study, reviewing a few dietary factors that clearly influence the risk of cancers along distractive tract and of other common types of cancer.
In the study, the researchers illustrated the association between diet and the risk of several types of cancer.
High-salt foods like Chinese style salted fish have been found to associated with Nasopharyngeal cancer and eating more fruits, vegetables and micronutrients such as vitamin C and folate could have a protective effect.
Like nasopharyngeal cancer, consuming large amounts of salted foods increase the risk of developing stomach cancer. Studies show that diets high in fruit and vegetables may help decrease the risk. Micronutrients like β carotene, selenium, and α tocopherol, polyphenols from green tea may have protective effects.
Obesity, alcohol, and smoke will increase the risk of developing oesophageal cancer. The lack of micronutrients is suspected to explain a high risk of oesophageal cancer while it has not been determined due to residual confounding from smoking and alcohol consumption. Additionally, hot beverages above 65°C is probably associated with an increased risk of oesophageal cancer.
Colorectal cancer is cancer highly associated with diet. Processed meat processed with potentially toxic chemicals like nitrates and nitrites have been listed as carcinogenic to humans. High consumptions of milk, calcium, vitamin D and dietary fiber are probably associated with a lower risk of colorectal cancer, indicated in some studies.
Alcohol is a well-known contributor to liver cancer, and obesity and chronic infection with hepatitis B or C viruses also increase risk. Aflatoxin, a mutagenic compound produced by certain fungi in foods like grains, nuts, and dried fruit is classified as a carcinogen, while coffee consumption may be weakly associated with a lower risk of developing liver cancer.
Obesity is associated with an increased risk of pancreatic cancer by about 20%, while it might play a role in breast cancer and prostate cancer but is not clear.
Some studies found that lycopene from tomatoes, micronutrients including β carotene, vitamin D, vitamin E, and selenium, and isoflavones largely from soya food may be probably associated with prostate cancer risk.
Smoking would increase the risk of developing lung cancer and diets higher in fruits, and vegetables might be associated with a slightly lower risk of lung cancer in smokers, but not in never smokers.
Diet has been found to associate with most types of cancer, whether weakly or strongly. The study listed some convincing nutritional factors identified by the World Cancer Research Fund (WCRF) and the International Agency for Research on Cancer (IARC) to be responsible for cancer risk increment. They are:
- Obesity. Cancer risk increases for every 5kg/m² rise in body mass index, varying from 5% for colorectal cancer to 50% for cancer of the endometrium.
- Alcohol. Cancer risk increases for each 10 g rise in alcohol consumption a day, vary from 4% for liver cancer to 25% for squamous cell carcinoma of the esophagus.
- Processed meat. The relative risk for colorectal cancer is high for each 50 g/day increment, and Chinese style salted fish is classified as a carcinogen.
- Foods contaminated with aflatoxin. Foods contaminated with aflatoxin can cause liver cancer.
Researchers also summarized a table listing some nutritional factors that are probably associated with increased cancer risk and decreased cancer risk, identified by WCRF and IARC.
Obesity and alcohol probably increase the risk of some types of cancer. Very hot drinks are probably associated with an increased risk of esophagus cancer. In contrast, a high glycaemic-containing diet may lower the risk of endometrial cancer, and coffee is probably protective for liver and endometrial cancer.
It is worth noting that acrylamide, a chemical produced mainly during high-temperature cooking, is included as a probable carcinogen to humans.
The study provides an overall outline of what we know about diet and cancer. Some diety factors, including obesity, alcohol, processed meat, etc, convincingly contribute to high cancer risk.
However, we are still not clear whether healthy diet factors like fruits and vegetables truly reduce cancer risk due to the presence of other involved determinants.
Key Timothy J, Bradbury Kathryn E, Perez Cornago Aurora, Sinha Rashmi, Tsilidis Konstantinos K, Tsugane Shoichiro et al. Diet, nutrition, and cancer risk: what do we know and what is the way forward? BMJ 2020; 368 :m511