Article - Effect of Polyphenol Supplementation on Memory Functioning in Overweight and Obese Adults: A Systematic Review and Meta-Analysis.

Expert Review

Reviewer: Nicky Ester

24th Apr 2025

Conflict of interest

None

Take home message

While it was not possible to identify which polyphenol (flavonoids, isoflavone and resveratrol) was the most effective, chronic polyphenol supplementation may benefit memory recall (immediate) in individuals who are overweight or obese and aged 60 or above.

Evidence category

A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)

Summary review

Introduction

This review focused on the effect of polyphenol supplementation on short-and long-term memory in overweight and obese individuals. Research highlights that overweight middle-aged individuals are at increased risk of cognitive impairment and Alzheimer’s disease (likely associated with chronic inflammation, including neuroinflammation).

Methods

A systematic search of PubMed/Medline, PsycInfo and Scopus was conducted for randomised controlled trials (RCTs) up to August 2023. Only English language studies were included.
Inclusion criteria (PICOS) – Overweight or obese adults >18 years, Body Mass Index ≥ 25kg/m2, only acute and/or chronic polyphenol-rich supplementation, control groups with food, juice or placebo and memory function tasks included.
Of 3330 publications, 24 met the inclusion criteria.
14 studies included both immediate and delayed retrieval tasks; five assessed delayed retrieval and five immediate retrieval.
Five crossover (CO) studies reported the acute effects of supplementation with single dosage up to 8 hours after administration and 19 between-participants design RCTs (BTW-P) examined chronic supplementation administered for up to 2.5 years.
2336 participants were included, with a mean age > 60.

Results

Immediate retrieval:

Level one meta-analyses - 16 RCT’s included. The weighted mean effect size for this random-effects analysis was significant (Hedges’ g= 0.170; 95% CI 0.007- 0.333; z = 2.044, p = 0.041), suggesting that polyphenol supplementation positively impacted immediate memory retrieval.
Level two meta-analyses – results from BTW-P supported this finding (g = 0.226, z = 2.209, p = 0.027), whereas CO studies did not (g = −0.007, z = −0.052).
Level three meta-analyses – by polyphenol type, were borderline nonsignificant (flavonoids) and nonsignificant (isoflavone, and resveratrol), suggesting a potential general benefit from polyphenol supplementation.

Delayed retrieval:

Level one meta-analyses - 16 studies included (Hedges’ g = 0.022; 95% CI −0.066-0.111; z = 0.499).
Level two meta-analyses - BTW-P results (g = 0.041, z = 0.854). CO results (g = 0.113, z = −0.867).
All results were nonsignificant, suggesting that polyphenol supplementation had no effect on delayed memory retrieval.

Conclusion

Chronic polyphenol supplementation may enhance immediate memory retrieval versus placebo.

Clinical practice applications

Mild cognitive impairment is a transitional stage between normal brain function and dementia. While the research is still not conclusive, given the inflammatory risks associated with being overweight or obese, chronic polyphenol supplementation including flavonoids, isoflavone and resveratrol, may benefit these client’s, especially those who are > 60 years of age and have a family history of dementia.

Considerations for future research

While the mean age of the study was >60, participants included could be of any age. Further studies could include reviewing the benefits of polyphenol supplementation on younger overweight/obese individuals to understand the impact it has on memory function.
Since studies included in the review did not all make a distinction between immediate and delayed retrieval, future research would benefit from more defined criteria and larger samples sizes.
More specific detail around polyphenol supplementation, including phenolic content would be recommended.

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Abstract

Negative health consequences of obesity include impaired neuronal functioning and cell death, thus bringing the risk of impaired cognitive functioning. Antioxidant properties of polyphenols offer a possible intervention for overweight people, but evidence for their effectiveness in supporting cognitive functioning is mixed. This review examined evidence from randomized controlled trials concerning the effect of polyphenols on tasks requiring either immediate or delayed retrieval of learned information, respectively, thus controlling for differences in cognitive processes and related neural substrates supporting respective task demands. Searches of the PubMed/Medline, PsycInfo, and Scopus databases identified 24 relevant primary studies with N = 2336 participants having a BMI ≥ 25.0 kg/m. The participants' mean age for the 24 studies exceeded 60 years. Respective meta-analyses produced a significant summary effect for immediate retrieval but not for delayed retrieval. The present findings support a potential positive effect of chronic supplementation with polyphenols, most notably flavonoids, on immediate retrieval in participants aged over 60 years with obesity being a risk factor for cognitive impairment. We recommend further investigation of this potential positive effect in participants with such risk factors. Future research on all populations should report the phenolic content of the supplementation administered and be specific regarding the cognitive processes tested.