Dietary index for gut microbiota is inversely associated with colorectal cancer risk: a case-control study

Gut microbial dysbiosis is a recognized contributor to colorectal cancer (CRC) development, with diet serving as a primary modifiable factor influencing microbiota composition. While previous research has largely focused on individual nutrients or the inflammatory potential of diet, few studies have investigated dietary patterns explicitly designed to support gut microbiota health in relation to CRC risk.

In this case-control study, 350 adults (175 newly diagnosed CRC patients and 175 age- and sex-matched controls) were recruited. Dietary intake was assessed using multiple 24-h recalls and a validated food-frequency questionnaire to calculate the Dietary Index for Gut Microbiota (DI-GM), which emphasizes prebiotic fibers, polyphenols, fermented foods, fruits, vegetables, legumes, and whole grains, while penalizing ultra-processed and pro-inflammatory foods. Anthropometric, lifestyle, inflammatory (CRP, IL-6), frailty (mFI-5), intestinal permeability, and psychological indicators were measured. Logistic regression estimated CRC odds across DI-GM tertiles, adjusting for potential confounders.

CRC patients had significantly lower DI-GM scores than controls (7.29 ± 2.70 vs. 11.34 ± 2.55; p < 0.001). Higher DI-GM scores were associated with lower systemic inflammation, lower frailty, and fewer depressive and sleep-related symptoms. Individuals in the highest DI-GM tertile had 68% lower odds of CRC compared with the lowest (OR = 0.32; 95% CI 0.19-0.55; P-trend < 0.001).

Greater adherence to a gut microbiota-supportive dietary index is independently associated with a lower risk of colorectal cancer, as well as with more favorable profiles of systemic inflammation, gut barrier integrity, and psychosocial health. These findings highlight the potential of microbiota-targeted dietary strategies for CRC prevention and support the need for future prospective and interventional research.