Ellie Zolfagharifard — Daily Mail April 29, 2015
Black Americans who switched to a high-fibre African diet for a fortnight saw a dramatic drop in risk factors for colon cancer.
Meanwhile, a group of Africans who started eating American food rich in animal proteins and fats saw their risks rise over the same short period.
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.
Colon cancer is the second biggest cause of cancer-related deaths of men and women in the U.S, with 136,000 new cases a year, and 50,000 deaths, according to the American Cancer Society.
In South Africa, colon cancer is far less prevalent, affecting five out of every 100,000 rural South Africans.
Globally colon cancer is the fourth deadliest form of the disease, killing more than 600,000 people a year.
The findings raised concerns about Western diet and about how the increasing ‘Westernisation’ 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.
To analyse the possible effects of diet and gut bacteria, scientists from Imperial College and the University of Pittsburgh worked with a group of 20 African American volunteers and 20 from rural South Africa.
‘Animal protein and fat intake was two to three times higher in Americans, whereas carbohydrate and fibre, chiefly in the form of resistant starch, were higher in Africans,’ they wrote in their report, published in the journal Nature Communications.
Fibre is main component of African dishes, many of which are plant-based. In comparison, junk food in US can lack fibre because the foods are largely processed.
The volunteers had colonoscopy examinations before and after the diet swap.
The researchers also measured biological markers that indicate colon cancer risk and studied samples of bacteria taken from the colon.
At the start, when the groups had been eating their normal diets, almost half of the American subjects had polyps – abnormal growths in the bowel lining that may be harmless but can progress to cancer.
None of the Africans had these abnormalities.
After two weeks on the African diet, the American group had significantly less inflammation in the colon and reduced biomarkers of cancer risk.
In the African group, measurements indicating cancer risk dramatically increased after two weeks 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