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.