Date of Award

Fall 2022

Document Type

Open Access Dissertation


Epidemiology and Biostatistics

First Advisor

Susan E. Steck


Introduction: Diet serves as a driving force for shaping the gut microbiome. Understanding how diet may modify gut microbiota and subsequently may be associated with chronic disease is critical to public health prevention efforts. Aims: We aimed to develop a novel dietary index that captures the quality of diet with respect to attaining beneficial composition and function of gut microbiota. We then examined the relationship between the dietary index and two gut microbiota-related cancers, i.e., colorectal and breast cancers.

Methods: We conducted a systematic review of studies that examined the effect of foods on gut microbiota in adult populations. Dietary components with evidence of beneficial or harmful effects on gut microbiota were used to build the novel dietary index for gut microbiota (DI-GM). In a large cross-sectional study, we examined the association between DI-GM and indirect biomarkers of gut microbiota diversity using linear regression analysis. In a prospective cohort study, Cox proportional hazard models were used to examine the association between DI-GM and risk of colorectal and breast cancers.

Results: Based on the literature review, 14 foods were included in the DI-GM: fermented dairy, chickpeas, soybean, whole grains, fiber, cranberries, avocados, broccoli, coffee, green tea, red meat, processed meat, refined grains, and high-fat diet (≥40% of energy). Each component was scored 0 or 1 based on sex-specific median intakes, and scores were summed to develop the DI-GM score. We found positive associations between DI-GM and markers of gut microbiota diversity. During < 5 years of follow-up, those with higher DI-GM scores (higher diet quality) had an 18% lower risk of incident colorectal cancer (HRadjusted= 0.82, 95% CI: 0.63, 1.07) compared to those with lower scores, though there was no association during ≥ 5 years of follow-up (HRadjusted=1.01, 95% CI: 0.80, 1.26). Females with higher DI-GM scores had a 10% reduced risk of breast cancer compared to those with lower scores (HRadjusted= 0.90, 95% CI: 0.79, 1.07).

Conclusions: A novel literature-derived dietary index, the DI-GM, was developed to score dietary intake in relation to gut microbiota composition and function. Using the DI-GM, we showed that diet quality related to the composition and function of gut microbiota may be related to the development of colorectal and breast cancers.


© 2022, Bezawit Eyob Kase

Available for download on Sunday, December 15, 2024

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