Did you know that the tiny critters living in your stomach play a role larger than life? Whether regulating blood sugar, boosting the immune system or even influencing your mood, these communities of bacteria, viruses, fungi and other microorganisms—collectively known as the gut microbiome—have a say in a panoply of physiological processes.

When you eat fermented foods such as kimchi, these microbes revel in a bounty of probiotics. But when you consume too many unhealthy foods, such as those that are ultra-processed, they get upset, which could lead to broader physiological repercussions.

Sometimes, an imbalanced microbiome can contribute to various health issues, such as the growth of pre-cancerous colorectal polyps. This link has recently been strengthened by a study led by Dr Jonathan Lee, Consultant in the Division of Gastroenterology & Hepatology, Department of Medicine, National University Hospital (NUH), who brought to light specific bacterial types that associate with the presence of tubular adenomas (TAs) and sessile serrated adenomas (SSAs), two types of pre-cancerous polyps.

Given that these polyps have the tendency to evolve into colorectal cancer—the second most common cause of cancer-related fatalities in Singapore—pinpointing these associated microbes could facilitate early detection and enable more focused preventative strategies.

The study analysed stool samples from a diverse cohort, comprising 971 individuals undergoing routine endoscopic procedures. The researchers identified 19 bacterial species significantly associated with TAs and eight with SSAs, distinguishing them from the non-adenoma group. Using these bacterial signatures, the Adenoma Microbial Dysbiosis Index was created, serving as a tool to refine the accuracy of detecting these polyps.

Looking into how these microbes process certain compounds offers important clues too. “For instance, patients with TAs had fewer microbial enzymes that metabolise methane and more that metabolise amino acids and lipids, while those with SSAs had more microbes that metabolise sulphates and secondary bile acids,” says Dr Lee. “Such findings could one day advance colorectal cancer screening by directly contributing to novel screening strategies incorporating microbial testing.” 

The study goes further, correlating specific demographic and environmental factors with the presence of these microbial signatures. Key influences include age, sex, body mass index, dietary patterns and certain medications like metformin and proton pump inhibitors.

These insights underscore the profound impact of lifestyle choices on the gut microbiome and, by extension, on the risk of developing colorectal cancer. In particular, the researchers found that certain bacteria associated with TAs, such as Flavonifractor plautii and Bacteroides stercoris, were noticeably less abundant in individuals consuming a vegetable-rich diet or those using Aspirin.

“When it comes to what you eat, a diet high in fibre, including fruits, vegetables, nuts and seeds, while minimising processed foods, nurtures beneficial bacterial and plays a crucial role in curbing the development of colorectal cancer,” says Dr Lee, highlighting the dietary angle of the study. “We’re looking forward to advancing this line of research, as deciphering how gut bacteria influence colorectal cancer susceptibility can potentially lead to novel therapeutic and dietary strategies to combat this disease.”