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Swap Your Diet, Swap Your Cancer Risk, New Study Finds

If you weren’t quite convinced that you are, at least mostly, what you eat, a new study should help persuade you. Researchers from the University of Pittsburgh, Imperial College London, Wageningen University in the Netherlands, University of Helsinki, University of Illinois, and the University of KwaZulu-Natal in South Africa followed participants in the U.S. and in South Africa, asking each group to switch to the diet of the other country. That is, African-American people in the U.S. ate a South African diet for two weeks, and South African people eat an American diet for two weeks. The switch, though brief, effected some pretty impressive changes in both groups of participants, from inflammatory markers to gut microbes. Though the study can’t prove that cancer incidence would have risen in the African participants had they continued an American diet over the long-term, based on the markers that arose, the authors say it’s probably a pretty good bet.

Colon cancer is the third most common form of cancer, and responsible for almost 700,000 deaths worldwide each year.


(AP Photo/Anjum Naveed)

Stephen O’Keefe, a professor at University of Pittsburgh School of Medicine, had noticed during his medical practice in South Africa that his patients’ colon health was chronically excellent: They rarely had polyps upon colonoscopy, and they rarely had colon cancer at all. In contrast, in the U.S., colon cancer is the second leading killer of all cancers, and African-Americans have the greatest risk of all groups in the U.S. Previous studies have shown that it takes just one generation for people who immigrate from non-Western countries to assume the cancer risk of America. Though the culprit is strongly believed to be the change in diet, it could theoretically be other things, like cigarettes, chemicals, infections and antibiotics. Therefore, O’Keefe and his team wanted to see what would happen in Africans and African-Americans switched diets for just two weeks.

So they had 20 people in each country, aged 50-65, assume the diet of the other. The Americans ate the typical low-fat, high fiber diet of South Africa: Foods included hi-maize corn fritters, salmon croquettes, and spinach, red pepper and onions for breakfast; hi-maize corn dogs or veggie dogs, homemade tater tots, and mango slices for lunch; and okra, tomatoes, and hi-maize meal; corn muffins, black-eyed peas, pineapple and black tea for dinner. Meanwhile, people in South Africa ate an “American” high-fat, low-fiber diet: Foods included beef sausage links and pancakes for breakfast; hamburger and French fries for lunch; and meatloaf and rice for dinner.

The researchers took blood samples, fecal samples, and had everyone have a colonoscopy before and after the diet intervention.

And the changes for both groups of people were marked. The turnover rate of the intestinal cells of American participants slowed considerably at the end of the two weeks, which is linked reduced cancer risk; in the South Africans participants, on the other hand, it sped up, a sign of increased cancer risk. Markers of inflammation increased in the South Africans who ate an American diet, and these same markers decreased in the Americans who ate the South African diet.

Finally, and perhaps most importantly, the composition of the gut bacteria of the two groups shifted over the two-week period. After the diet intervention, the African-American participants had an increase in butyrate production in the gut, which is linked to reduced colon cancer risk, and the African group showed a reciprocal drop in butyrate. The authors say these shifts reflect changes in the makeup of each group’s gut bacteria, which are increasingly thought to influence our health in many ways, from metabolic health to mental health. And the new study supports that connection, at least when it comes to colon cancer risk.

“These findings are really very good news,” said O’Keefe. “In just two weeks, a change in diet from a Westernized composition to a traditional African high-fiber, low-fat diet reduced these biomarkers of cancer risk, indicating that it is likely never too late to modify the risk of colon cancer.” Of course, the study can’t determine whether the change in diet would have led to more colon cancer in the African participants if they’d continued it for years. But the authors say that the changes they saw were very likely signs of increased cancer risk.

The authors argue that the high-fiber element of the African diet is likely what’s behind the shift, at least in large part – previous studies have found that 50 grams/day of fiber is generally what’s needed to reduce colon cancer risk, and this is about what the American participants’ fiber intake rose to when they switched to an African diet. Less than this, based on earlier evidence, doesn’t seem to do the trick.

The results also call out a larger issue: That the increasing Westernization of dietary habits across the world is probably not a good thing. If you eat any kind of diet that’s decidedly not American – Mediterranean, vegetarian, African, or anything else that’s high-fiber and plant-based – you’ll probably want to keep it up. And, based on the accumulating evidence, if you’ve fallen into the sticky clutches of the Western diet, whether you live in the U.S. or not, it’s probably smart to try and clamber out.

Also on Forbes:

A Quick Guide To The Mediterranean Diet

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