Abstract

A healthy diet has long been indicated to be protective against Alzheimer's diseases (AD). We carried out a systematic review and meta-analysis of published observational studies to explore the relationship between healthy and unhealthy diets and risk of ADs. We screened PubMed, Scopus, Web of Sciences, Google Scholar, Science Direct, and Embase, and screened manually to identify relevant articles published in English and non-English until Jun 2020. We classified the studied dietary patterns into two groups: healthy and unhealthy diets. The pooled weighted mean difference and 95 confidence interval (95 CI) was used to analyze the data using a random-effects model. The data were extracted manually and the preferred reporting items for systematic review and meta-analysis checklist was used to appraise the risk of bias and quality of data. Of the 1,813 articles identified, 21 met the inclusion criteria and were included in the quantitative analysis. A healthy diet was related to a lower risk of AD odds ratio (OR): 0.45, 95% CI: 0.23 to 0.86, I(2)=99.7%; n=17 studies. Moreover, high adherence to an unhealthy diet was not associated with increased risk of AD (OR: 0.99, 95% CI: 0.98 to 0.99, I(2)=0.0%; n=6 studies). However, the etiology of AD is uncertain and it is difficult draw conclusions about dietary healthy patterns. We concluded that adherence to a healthy diet is associated with a lower risk of AD, but were unable to find evidence that an unhealthy diet increases the risk of AD.