Diet and biomarkers of Alzheimer's disease: a systematic review and meta-analysis.

Alzheimer's disease (AD) risk increases with age and lacks efficacious pharmacological options. Summaries of the existing evidence reveal an association between Mediterranean-style diet adherence and reduced AD incidence; however, no review has investigated this relationship with respect to the hallmark AD biomarkers (tau and beta-amyloid) that manifest decades before clinical symptomatology. MEDLINE, PubMed, PsycINFO, Google Scholar, and SCOPUS databases were systematically searched to identify peer-reviewed articles investigating diet and AD biomarkers in the last 2 decades. Two thousand seven hundred twenty-six records were extracted, quality assessed, and double-blind screened by 2 authors. Fifteen studies met the inclusion criteria and 13 studies found a significant relationship. Of these, 4 studies found a high-glycemic load was related to an increase in AD biomarker burden; 6 found adherence to a Mediterranean or "AD-protective" dietary pattern conferred a reduction in AD biomarker burden. Meta-analysis revealed a small but significant effect of diet on AD biomarkers (β = 0.11 [95% CI 0.04-0.17], p = 0.002). This systematic review supports the notion that diet and nutrition display potential for nonpharmacological AD prevention.