Colorectal cancer cases in young adults are rising. Scientists blame poor gut health from unhealthy diets

Doctors recommend colorectal cancer screenings starting at 45, yet this may not be soon enough. The number of colorectal cancer diagnoses in people under 50 has risen in the past decade by 2%. New research from the University of Cincinnati’s College of Medicine suggests the cause for an increase in cases among young adults is the gut microbiome and what people nowadays are feeding it.

“When I started practice and residency around 2010, I’d uncommonly see patients who were less than 50 years old,” says Dr. Jordan Kharofa, an associate professor in the Department of Radiation Oncology at the school, in a university release. “But more and more we’re seeing these patients in our clinics now to the point where it doesn’t strike us as an exception to the rule.”

One reason people had trouble connecting the gut’s role in colorectal cancer is insufficient tools to study it. Advances in DNA sequencing over the past decade have made it possible to better study the microbiome and specific bacterial species that inhabit it. “In the past, we’d have to culture specific bacteria and isolate them, and that’s really complicated,” Kharofa explains. “But now with the genetics and the cost of sequencing going down, we can quickly characterize what species are where and try to understand if they have implications for normal health and disease.”

Previous research has now linked specific bacterial species in the gut with colorectal cancer. While science has shown a light on the presence of cancer-causing bacteria, it’s unknown whether some of these species are more prominent in younger people with colorectal cancer versus older adults with the disease.

For their research, the team collected genetic data from 11 other studies which contain information on the microbiome of 609 people, as well as 692 with colorectal cancer.

There were some age-related differences in the gut bacteria that are associated with colorectal cancer. Two bacterial species linked to colorectal cancer were not elevated among younger patients. This suggests these bacteria are not the cause of rising cancer diagnoses in young people.

Instead, the team spotted five other bacterial species at high levels in the microbiome of young patients with colorectal cancer. One bacterial species comes from a sulfur microbial diet while the other comes from eating a diet high in processed meats, low-calories drinks, alcohol, and low in raw fruits, vegetables, and legumes.

The results are consistent with another finding that studied stool samples from young people. They found a higher risk of cancer in young people who adhere to a sulfur microbial diet.

“Although these patients aren’t obese, there may be dietary patterns that happen early in life that enrich for certain bacteria such as this one,” Kharofa says. “It’s not that what you’re eating has carcinogens in them, but the byproducts produced during bacteria metabolism may lead to carcinogenic chemicals. It’s possible that interactions between diet and the microbiome may mediate the formation of colorectal cancer cells and heightened risk in younger populations over the last several decades.” 

The grand takeaway the researchers want people to know is that the microbiome influences a young person’s cancer risk, but it may start with what you eat. Kharofa urges young people to eat more raw fruits, vegetables, and legumes and reduce the amount of processed meat they consume everyday.

“There’s still a lot we don’t understand about how the diet influences the microbiome and how that might influence cancer, but this is a small sneak peek at something that might be going on,” explains Kharofa. 

The next step in the research is to see how the elevated bacterial species in young adults affect the development of cancer and cancer treatment effectiveness. Looking ahead, if the role of gut bacteria in cancer becomes clearer, there is a possibility of creating personalized screenings for young adults.

“It’s really difficult to just screen everybody because the rates are pretty low in the entire population of individuals less than 45 years old,” says Kharofa. “But if you are able to profile the microbiome and maybe do targeted screening in some patients who had higher risk based on their stool, that might be a worthwhile investigation.”

The research findings were presented at the American Society of Clinical Oncology (ASCO) annual meeting.

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