Association between the dietary index for gut microbiota and Alzheimer's disease: A cross-sectional study from the National Health and Nutrition Examination Survey (2004 to 2018).

Introduction: Emerging evidence implicates gut microbiota (GM), shaped by diet, in Alzheimer's disease (AD) pathogenesis. However, the association between the dietary index for GM (DI-GM) and AD remains unclear.

Methods: This cross-sectional study analyzed data from 28,830 adults aged ≥20 years in the 2004-2018 National Health and Nutrition Examination Survey (NHANES). The DI-GM score, derived from dietary recalls, comprised beneficial to GM score (BGMS) and unfavorable to GM score (UGMS) components. AD was identified via self-report, medications, or death certificates. Multivariable weighted logistic regression, restricted cubic spline, and subgroup analyses were performed.

Results: Contrary to expectations, higher DI-GM score and UGMS were associated with increased AD prevalence (DI-GM: odds ratio [OR] = 1.24, 95% CI: 1.02 to 1.52, p = 0.033; UGMS: OR = 1.36, 95% CI: 1.10 to 1.69, p = 0.005).

Discussion: The DI-GM was positively associated with AD prevalence, suggesting that imbalanced plant-based diets low in protein or key nutrients may elevate AD risk despite presumed microbiota benefits.

Highlights: Higher DI-GM and UGMS were significantly associated with greater AD prevalence in US adults.Restricted cubic spline analyses showed linear and non-linear associations of DI-GM and UGMS with AD, respectively.Results challenge prior assumptions that higher DI-GM scores are uniformly linked to health benefits.Imbalanced plant-based diets low in protein or key nutrients may adversely affect cognitive aging despite presumed microbiota benefits.