The study aimed to develop and evaluate a novel dietary index for gut microbiota (DI-GM) that captures dietary composition related to gut microbiota profiles. A literature review of longitudinal studies on the association of diet with gut microbiota in adult populations identified 14 foods or nutrients as components of the DI-GM, including fermented dairy, chickpeas, soybean, whole grains, fiber, cranberries, avocados, broccoli, coffee, and green tea as beneficial components, and red meat, processed meat, refined grains, and a high-fat diet (≥40% of energy from fat) as unfavorable components. Each component was scored 0 or 1 based on sex-specific median intakes, and scores were summed to develop the overall DI-GM score. The DI-GM was computed using dietary data from the National Health and Nutrition Examination Survey (NHANES, 2005–2010, n = 3812), and associations with biomarkers of gut microbiota diversity (urinary enterodiol and enterolactone) were examined using linear regression. The DI-GM scores ranged from 0–13 with a mean of 4.8 (SE = 0.04). Positive associations between DI-GM and urinary enterodiol and enterolactone were observed, indicating enhanced gut microbiota diversity. The study demonstrates the potential utility of this index for gut health-related studies.The study aimed to develop and evaluate a novel dietary index for gut microbiota (DI-GM) that captures dietary composition related to gut microbiota profiles. A literature review of longitudinal studies on the association of diet with gut microbiota in adult populations identified 14 foods or nutrients as components of the DI-GM, including fermented dairy, chickpeas, soybean, whole grains, fiber, cranberries, avocados, broccoli, coffee, and green tea as beneficial components, and red meat, processed meat, refined grains, and a high-fat diet (≥40% of energy from fat) as unfavorable components. Each component was scored 0 or 1 based on sex-specific median intakes, and scores were summed to develop the overall DI-GM score. The DI-GM was computed using dietary data from the National Health and Nutrition Examination Survey (NHANES, 2005–2010, n = 3812), and associations with biomarkers of gut microbiota diversity (urinary enterodiol and enterolactone) were examined using linear regression. The DI-GM scores ranged from 0–13 with a mean of 4.8 (SE = 0.04). Positive associations between DI-GM and urinary enterodiol and enterolactone were observed, indicating enhanced gut microbiota diversity. The study demonstrates the potential utility of this index for gut health-related studies.