Conclusion Statement
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)
Plain Language Summary
What is the question?
- The question is: What is the relationship between dietary patterns consumed and neurocognitive health?
What is the answer to the question?
- 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.
Why was this question asked?
- 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.
How was this question answered?
- 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.
- 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.
What is the population of interest?
- For the intervention/exposure, children through older adults, age 2 years and older
- For the outcome, adults and older adults, age 19 years and older
What evidence was found?
- This review identified 26 articles that met inclusion criteria.
- Most studies reported dietary patterns consumed during adulthood relate to improved cognitive measures or lower risk of cognitive impairment. These dietary patterns were higher in vegetables, fruits, unsaturated vegetable oils and/or nuts, legumes, and fish or seafood.
- Many limitations in study design and conduct were identified in the included studies. This includes differences in dietary patterns examined, cognitive assessment methods, and lack of accounting for possible changes in diet over time.
- The 2020 Committee updates and builds on the conclusion drawn by the 2015 Committee from an existing systematic review.
How up-to-date is this systematic review?
- This review searched for studies published from January 2014 to February 2020, and updated an existing systematic review that included evidence from January 1980 to August 2014.
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Technical Abstract
Background
- 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.
- 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.
- 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
- 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
- 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
- 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.
- 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
- This systematic review update includes 26 articles that met inclusion criteria and were published between January 2014 and February 2020.
- Four studies were randomized controlled trials.
- Twenty-two articles were from observational studies, with 21 prospective cohort designs and 1 nested-case control design.
- 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
- 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.
- Outcomes were measured using various approaches and reported as global cognition, cognitive performance, mild cognitive impairment, and/or incident dementia.
- 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.
- 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.
- Non-significant findings or those reporting mixed associations reported dietary patterns consumed during adulthood did not worsen cognitive outcomes.
- 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.
- 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.
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Full Systematic Review
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Suggested Citation: Boushey C, Ard J, Bazzano L, Heymsfield S, Mayer-Davis E, Sabaté J, Snetselaar L, Van Horn L, Schneeman B, English LK, Bates M, Callahan E, Venkatramanan S, Butera G, Terry N, Obbagy J. Dietary Patterns and Neurocognitive Health: A Systematic Review. July 2020. U.S. Department of Agriculture, Food and Nutrition Service, Center for Nutrition Policy and Promotion, Nutrition Evidence Systematic Review. Available at: https://doi.org/10.52570/NESR.DGAC2020.SR0106
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