"This study supports a direct role of diet in modifying the gut microbiome in ways that might have an influence on the development of CRC," Dr. Andrew Chan of Massachusetts General Hospital and Harvard Medical School in Boston told Reuters Health by email.
"There is strong evidence linking diet to CRC risk and emerging evidence supporting a key role of the gut microbiome in CRC," he said. "However, specific data to show if the influence of diet on cancer risk was mediated through its influence on the gut microbiome was lacking. We sought to fill that evidence gap."
As reported in JAMA Network Open, the prospective cohort study included data from close to 215,000 health professionals who were free of inflammatory bowel disease and cancer at baseline. About 23% were men with a mean age of 54 at baseline the rest were women with a mean baseline age of 43.
Dr. Chan and colleagues created a diet score, developed by analyzing food-frequency questionnaires, that correlated with 43 sulfur-metabolizing bacteria identified through taxonomic and functional profiling of gut metagenome data.
A total of 3,217 (1.5%) cases of CRC were documented during 5,278,048 person-years of follow-up. The diet that promoted sulfur-metabolizing bacteria (dubbed "sulfur microbial diet") was identified in a subsample of 307 men (mean age, 70.5) and 212 women (mean age, 61.0), and was characterized by high intakes of low-calorie beverages, French fries, red meats, and processed meats, and low intakes of fruits, yellow vegetables, whole grains, legumes, leafy vegetables, and cruciferous vegetables.
After adjustment for other risk factors, greater adherence to the sulfur microbial diet was associated with an increased risk of CRC, with a hazard ratio of 1.27 when comparing the highest versus the lowest quintile of the diet score.
When assessed by anatomical subsites, greater adherence to the sulfur microbial diet was positively associated with distal CRC (HR, 1.25) but not proximal colon cancer (HR, 1.13).
Summing up, the authors state, "Adherence to the sulfur microbial diet was associated with an increased risk of CRC, suggesting a potential mediating role of sulfur-metabolizing bacteria in the association between diet and CRC. Further research is needed to confirm these findings and to determine the underlying mechanisms."
Dr. Chan added, "The next step will be to examine if diet could be modified in such a way as to encourage the development of a gut microbiome that has less sulfur-reducing bacteria to lower the risk of CRC."
Meanwhile, he added, "We should be counseling patients to eat a healthy diet, particularly avoiding foods that may promote the development of sulfur-reducing bacteria."
Dr. Jeffery Nelson, Surgical Director of Mercy's Center for Inflammatory Bowel and Colorectal Diseases in Baltimore, commented in an email to Reuters Health. "The findings seem reasonable, but this study shows association, not causation. It's interesting, because it does hone in a little bit on what might be involved in possible dietary causes of CRC. It makes sense that the microbiome would be involved in CRC development, and this has been implicated in other studies."
That said, he added, "We've been counseling people away from diets heavy in red meat and low calorie/diet drinks for quite some time (in addition to the other foods they mention). The importance of the study is that it potentially gives us a group of bacteria to focus on in future studies that may ultimately show the causation we're looking for."
SOURCE: https://bit.ly/3nJ3Tva JAMA Network Open, online November 12, 2021
By Marilynn Larkin
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