To test the true impact of diet on bowel cancer, researchers at the Imperial College London recruited 20 African Americans from Pittsburgh, Pennsylvania and gave them a meal plan based on a ‘traditional’ African diet high in fibre and low in fat, centred on corn-based products, vegetables, fruit, and pulses. Meanwhile, 20 African volunteers living in rural South Africa were given a typical Western diet, high in red meat and low in fruit, vegetables and other sources of fibre.
Participants had colonoscopy examinations to look for inflammation and polyps that can indicate potential cancer risk before commencement and after completion of the study. At the start of the study, nearly half of the Americans, and none of the South Africans, had polyps. But after only two weeks, the American group was found to have significantly reduced colon or bowel inflammation, while in the South Africans, measurements indicating cancer risk dramatically increased.
Professor Jeremy Nicholson from Imperial’s department of surgery and cancer commented on the findings: “What is really surprising is how quickly and dramatically the risk markers can switch in both groups following diet change.”The new study suggests that changing diet may affect cancer risk by altering the balance of bacteria found in the gut – known as the microbiome. At the start of the study the African group consumed between two and three times less animal protein and fat than the Americans, but consumed significantly more carbohydrate and fibre.
This led to higher levels of butyrate, a by-product made by the body when it metabolises fibre. Butyrate is thought to have anti-cancer effects, and higher levels were seen in the Americans after two weeks on the African diet.
Dr James Kinross, a colorectal surgeon and clinical lecturer at Imperial, comments: "Scientists are beginning to recognise that the gut microbiome could have an important influence on human health.This research shows that gut bacteria are critically important for mediating the link between diet and colon cancer risk. This means we can look to develop therapies targeting gut bacteria as a way to prevent and treat cancer.”
Professor Nicholson also raised the concern that the progressive westernisation of African communities may lead to the emergence of colon cancer as a major health issue for them.
Proceedings of the National Academy of Sciences USA. Study on the connection between red meat, inflammation and cancer progression.
Nature Communications Fat, Fibre and Cancer risk