I think you’re referring to a “diet swap” study in which African Americans in the U.S. switched diets with people living in rural South Africa. This was a small study that produced intriguing results, suggesting that a radical dietary change can dramatically lower colon cancer risk in just two weeks.
Researchers at the University of Pittsburg and Imperial College in London recruited 20 African Americans in the U.S. and 20 volunteers from rural South Africa. To begin, all the participants had colonoscopies, and the researchers examined and measured biological markers indicative of colon cancer risk. They also studied samples of colonic bacteria from all the volunteers. Almost half of the Americans – but none of the Africans – had polyps in the lining of their bowels. These growths can be harmless, but in some cases they can progress to cancer.
The diet swap involved the African Americans eating a high-fiber, low-fat African-style diet, while the Africans ate a Western-style diet high in fat and low in fiber. They were closely supervised for the two weeks of the experiment. All then had follow-up colonoscopies.
The result of the swap was rather remarkable. After the two weeks, the Americans had significantly less inflammation in their colons and reduced biomarkers of cancer risk. However, the Africans’ measurements showed a dramatic increase in markers of cancer risk.
We’ve known for some time that the low-fiber Western diet is linked to a much higher rate of colon cancer than are diets in Africa and the Far East. Diets high in red meat – especially those cooked at high temperatures – can increase risk, possibly due to chemicals created by heat and charring. The American Cancer Society reports that for reasons not yet understood, African Americans have the highest colorectal cancer incidence and mortality rates of all racial groups in the United States. Worldwide, colon cancer accounts for 600,000 deaths per year.
In a press release accompanying publication of the study, Imperial College professor Jeremy Nicholson said that it isn’t certain that the changes seen in the tests given the Africans after the two weeks would have led to cancer, but that there is “good evidence from other studies that the changes we observed are signs of cancer risk.”
The investigators also reported that the major reason for the changes in cancer risk observed was the way in which bacteria in the gut – the microbiome – altered their metabolism to adapt to the new diets. They found that the African diet led to an increase in production of butyrate, a byproduct of fiber metabolism that has important anti-cancer effects. This is good news since it suggests that treatments might be developed targeting gut bacteria as a way to prevent cancer.
The other important message from this study is to reinforce the recommendation that people can lower their colon cancer risk by boosting their fiber intake, and that this positive change could come about quickly.
Andrew Weil, M.D.
S.J.D. O’Keefe et al. “Fat, fibre and cancer risk in African Americans and rural Africans.” Nature Communications, 2015. DOI: 10.1038/ncomms7342