Dietary Patterns and Neurocognitive Health: A Systematic Review [Internet]

Excerpt

Background:

1. This important public health question was identified by the U.S. Departments of Agriculture (USDA) and Health and Human Services (HHS) to be examined by the 2020 Dietary Guidelines Advisory Committee.

2. The 2020 Dietary Guidelines Advisory Committee, Dietary Patterns Subcommittee conducted a systematic review to answer this question with support from the Nutrition Evidence Systematic Review (NESR) team.

3. The goal of this systematic review was to examine the following question: What is the relationship between dietary patterns consumed and neurocognitive health?

Conclusion statement and grade:

1. Limited evidence suggests that dietary patterns containing vegetables, fruits, unsaturated vegetable oils and/or nuts, legumes, and fish or seafood consumed during adulthood are associated with lower risk of age-related cognitive impairment and/or dementia. (Grade: Limited)

Methods:

1. Two literature searches were conducted using 3 databases (PubMed, Cochrane, Embase) to identify articles that evaluated the intervention or exposure of dietary patterns consumed and the outcomes of neurocognitive health. A manual search was conducted to identify articles that may not have been included in the electronic databases searched. Articles were screened by two NESR analysts independently for inclusion based on pre-determined criteria

2. Data extraction and risk of bias assessment were conducted for each included study, and both were checked for accuracy. The Committee qualitatively synthesized the body of evidence to inform development of a conclusion statement(s), and graded the strength of evidence using pre-established criteria for risk of bias, consistency, directness, precision, and generalizability.

3. Dietary patterns were defined as the quantities, proportions, variety, or combination of different foods, drinks, and nutrients (when available) in diets, and the frequency with which they are habitually consumed.

Summary of the evidence:

1. This systematic review update includes 26 articles that met inclusion criteria and were published between January 2014 and February 2020.

   1. ○

      Four studies were randomized controlled trials.

   2. ○

      Twenty-two articles were from observational studies, with 21 prospective cohort designs and 1 nested-case control design.

2. Studies in this update to the existing review produced similarly consistent results regarding the relationship between dietary patterns in adults and age-related cognitive decline, mild cognitive impairment, and/or dementia

3. Dietary patterns were examined using various approaches including 17 studies that examined adherence to a dietary pattern using indices/scores, 4 articles identified dietary patterns using factor/cluster analysis, and 1 study used reduced rank regression.

4. Outcomes were measured using various approaches and reported as global cognition, cognitive performance, mild cognitive impairment, and/or incident dementia.

5. The majority of significant findings reported dietary patterns consumed during adulthood were “protective” in either improving measures of cognitive impairment and/or reducing risk of cognitive impairment or dementia. These protective dietary patterns contained vegetables, fruits, unsaturated vegetable oils and/or nuts, legumes, and fish or seafood. Many of these dietary patterns also emphasized whole grains, non-refined grains, or (non-refined) breads/cereals.

6. Not all of these protective dietary patterns contained alcoholic beverages. The benefit of the overall dietary pattern with the outcome was still observed if alcoholic beverages, particularly red wine, were included.

7. Non-significant findings or those reporting mixed associations reported dietary patterns consumed during adulthood did not worsen cognitive outcomes.

8. There are numerous limitations across the body of evidence, including the lack of RCT’s, considerable variation in testing methods used, validity and reliability of the methods used, the dietary patterns and cognitive outcomes examined.

9. This body of evidence updates and builds upon the conclusion drawn by the 2015 Dietary Guidelines Advisory Committee in an existing systematic review, which consisted of 30 articles from a wide range of study designs that used different methods to measure neurocognitive outcomes but produced relatively consistent findings.