Beware of what you eat, because an unhealthy Western diet reportedly increases your risk of developing colon cancer.

That's at least according to a new study published in the journal Nature Communications, which details how scientists have found dramatic effects on risk factors for colon cancer when American and African volunteers swapped diets for just two weeks.

Western diets, which are high in protein and fat but low in fiber, are thought to raise colon cancer risk compared with African diets high in fiber and low in fat and protein. And now researchers at the Imperial College London (ICL) have confirmed that lots of fiber is the key to staving off colon cancer, with gut bacteria also playing a crucial role.

Colon cancer is the fourth leading cancer killer worldwide, accounting for over 600,000 deaths per year. Colon cancer rates are much higher in the western world than in Africa or the Far East, and yet in the United States, African Americans shoulder the greatest burden of the disease.

To investigate how diet may come into play, an international team of scientists from ICL and the University of Pittsburgh looked at a group of 40 volunteers, half of them African American and half of them from rural South Africa. The two groups swapped diets under tightly controlled conditions for two weeks, undergoing a colonoscopy examination both before and after the diet change. The researchers also measured biological markers that indicate colon cancer risk and studied samples of bacteria taken from the colon.

Before the swap, almost half of the American subjects had polyps - abnormal growths in the bowel lining that could possibly lead to cancer. Meanwhile, none of the Africans had these potentially life-threatening abnormalities. (Scroll to read on...)

But after two weeks on the African diet, the American group had significantly less inflammation in the colon and reduced biomarkers of cancer risk. On the other hand, the African group's risk of colon cancer dramatically increased after two weeks on the western diet.

"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," lead researcher Professor Jeremy Nicholson from ICL said in a news release.

"The findings suggest that people can substantially lower their risk of colon cancer by eating more fiber. This is not new in itself," he added, "but what is really surprising is how quickly and dramatically the risk markers can switch in both groups following diet change. These findings also raise serious concerns that the progressive westernization of African communities may lead to the emergence of colon cancer as a major health issue."

So what is it exactly about the low-fiber Western diet that makes it such a significant risk for developing colon cancer? Nicholson and his colleagues suggest that the answer lies with gut bacteria (microbiome) in the body. That is, when participants adapted to a new diet, their gut bacteria altered their metabolism in a way that affected their risk for color cancer.

In the American group, for example, the researchers found that the African diet led to an increase in the production of butyrate - a byproduct of fiber metabolism that has important anti-cancer effects.

"The gut microbiome is being increasingly recognized as an important contributor to human health," noted Dr. James Kinross, one of the researchers. "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."

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