High-fat diets could be driving America’s colorectal cancer epidemic in young people, a study suggests. Researchers at the Salk Institute and the University of California, San Diego, found that high-fat diets change gut bacteria and alter digestive molecules called bile acids in mice. These caused inflammation, which increased the chance of colorectal cancer, a notoriously difficult-to-treat type of the disease.
While only studied in mice, the study may provide one of the first clues as to what’s causing the spike in colorectal cancer cases in young Americans, which have doubled inexplicably in the last two decades. Other factors like sugar, C-sections, and even a fungal infection have also been touted as possible causes.
Dr Ronald Evans, study author and director of the Salk Institute’s Gene Expression Laboratory, said: ‘The balance of microbes in the gut is shaped by diet, and we are discovering how alterations in the gut microbial population (the gut microbiome) can create problems that lead to cancer.
‘This paves the way toward interventions that decrease cancer risk.’ It’s unclear what specific foods the mice ate or how much fat was in them, but it’s safe to assume they were meant to emulate high-fat foods that are staples of the American diet, like fast food.
The study builds on Dr Evans’ previous research, which found that mice who ate high-fat diets had higher bile acid levels. Bile acids are molecules produced by the liver that help the gut digest food and absorb cholesterol, fats, and nutrients.
The researchers suggested that the shift in bile acids shut down a key protein in the gut called the Farnesoid X receptor (FXR), increasing the prevalence of colorectal cancer.
In the new study, Dr. Evans and his team found that modified bile acids affected the production of stem cells in the intestines. When these don’t replenish frequently enough, they can cause mutations that encourage cancer cell growth.
High-fat diets, they said, change the composition of the microbiome, encouraging the growth of bacteria that boosts bile acid production. This creates a vicious cycle of inflammation.
Study author Dr Michael Downes said: ‘We are only just beginning to understand these bacterially-conjugated bile acids and their roles in health and disease.’
‘We’ve deconstructed why high-fat diets aren’t good for you, and identified specific strains of microbes that flare with high-fat diets, Dr Evans said. ‘By knowing what the problem is, we have a much better idea of how to prevent and reverse it.’
Colorectal cancer rates are on the rise worldwide, causing an epidemic in young people. Rates are expected to double in young people by 2030, and colorectal cancer is also expected to become the leading cause of cancer deaths in people under 50 by the end of the decade.
