• The findings of a study suggest that yogurt consumption can modify the microbiome, leading to a protective effect against certain types of colorectal cancer.
• Researchers observed that the rate of colon cancer incidence is 20 per cent lower with yogurt intake two or more times a week.
• The lower rate refers to a reduced incidence of proximal colorectal cancer, in the right side of the colon.

Long-term yogurt consumption may protect against colorectal cancer through changes in the gut microbiome: that is what a study conducted by researchers at the Harvard T.H. Chan School of Public Health and Mass General Brigham, published on 12 February in Gut Microbes, has found.

"Our study provides unique evidence on the potential benefits of yogurt," said Shuji Ogino, professor in the Department of Epidemiology at Harvard T.H. Chan School and one of the study's authors. "My lab's approach is to try to link long-term diets and other exposures to a possible fundamental difference in tissues, such as the presence or absence of a particular bacterial species. This kind of investigative work can strengthen the evidence linking diet to health outcomes."

Yogurt and colorectal cancer, the study

The researchers used data from two prospective cohort studies in the United States known as the Nurses' Health Study (NHS), involving 100,000 nurses, and the Health Professionals Follow-up Study (HPFS), involving 51,000 male health professionals. Participants were followed from 1976 for the NHS and from 1986 for the HPFS, completing questionnaires on lifestyle and health status.

They identified 3,079 documented cases of colorectal cancer across the two study populations. Information on Bifidobacterium content was available in 1,121 cases. Of these, 346 cases (31 per cent) were Bifidobacterium-positive and 775 cases (69 per cent) were Bifidobacterium-negative.

The scientists did not observe a significant association between long-term yogurt consumption and overall colorectal cancer incidence, but they did note an association in Bifidobacterium-positive tumours, with an incidence rate 20 per cent lower among participants who consumed two or more servings of yogurt per week. This lower rate was driven by a reduced incidence of proximal colon cancer based on the abundance of Bifidobacterium tumour tissue. Proximal colon cancer occurs in the right side of the colon and is more aggressive than distal colon cancer, which occurs on the left side.

The findings suggest that yogurt consumption can modify the gut microbiome, leading to a protective effect against certain types of colorectal cancer. "Yogurt and other fermented dairy products have long been thought to be beneficial for gastrointestinal health," said study co-senior author Tomotaka Ugai. "Our new findings suggest that this protective effect may be specific to Bifidobacterium-positive tumours."

The study adds to the growing body of evidence illustrating the connection between diet, the gut microbiome and colorectal cancer risk, but further research bringing together both basic science and population health studies is needed to draw a definitive conclusion.