London - Black Americans who switched to a high-fibre African diet for just two weeks saw a dramatic drop in risk factors for colon cancer, a study published on Tuesday found.
A group of Africans from KwaZulu-Natal who went the other way and started eating American food rich in animal proteins and fats saw their risks rise over the same short period, according to the paper in the journal Nature Communications.
Researchers said they were not surprised that eating more fibre appeared to lower colon cancer risk, but were struck by how quickly and dramatically the effects showed.
The findings raised concerns about Western diet and about how the increasing "Westernization" of diets in Africa could turn colon cancer into a major health issue there, said Jeremy Nicholson from Imperial College London who co-led the study.
Colon cancer is the fourth deadliest form of the disease, killing more than 600,000 people a year. Rates are much higher in Western countries than in Africa or the Far East.
To analyse the possible effects of diet and gut bacteria, scientists from Imperial College and the University of Pittsburgh in the United States worked with a group of 20 African American volunteers and 20 from rural KZN, the Guardian reports.
The Independent reports that researchers gave the Amercians from Pittsburgh, Pennsylvania 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, the KZN volunteers were given a typical Western diet, with plenty of red meat, but precious little fruit and vegetables or other sources of fibre.
In the American group, two weeks on the African diet led to significantly less inflammation in the colon and reduced biomarkers of cancer risk.
In the African group, measurements of cancer risk dramatically increased after 14 days on the Western diet, with lots of food like meat and cheese.
"We can't definitively tell from these measurements that the change in their diet would have led to more cancer in the African group or less in the American group, but there is good evidence from other studies that the changes we observed are signs of cancer risk," said Nicholson.
The analysis found one of the main reasons for the risk changes was the way in which bacteria in the gut - known as the microbiome - changed their metabolism to adapt to the new diet.
In the American group, the African diet led to a rise in the production of butyrate, a by-product of fibre metabolism that has important anti-cancer effects, the researchers said.
"Africanisation" of the diet increased total quantities of butyrate in one measure by 2.5 times, while "Westernisation" reduced quantities by half, they wrote in their study.
Reuters
Diet swap: What the volunteers ate on day one
A high fibre, low fat rural South African diet for the Americans included corn fritters, spinach and red pepper for breakfast; corn dogs, fried potatoes and mango for lunch; and tomatoes, corn muffins and black-eyed peas for dinner.
A high fat, high protein American diet for the South Africans included beef sausage and pancakes for breakfast; burger and chips for lunch; and meatloaf and rice for dinner.
The Independent