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Am J Clin Nutr. 2020 Mar 1;111(3):590-600. doi: 10.1093/ajcn/nqz328.

Effect of a 2-year diet intervention with walnuts on cognitive decline. The Walnuts And Healthy Aging (WAHA) study: a randomized controlled trial.

Author information

1
Lipid Clinic, Endocrinology and Nutrition Service, Hospital Clínic, Biomedical Research Institute August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
2
CIBER Pathophysiology of Obesity and Nutrition (CIBEROBN), Carlos III Health Institute, Madrid, Spain.
3
Barcelonaßeta Brain Research Center, Pasqual Maragall Foundation, Barcelona, Spain.
4
Center for Nutrition, Healthy Lifestyle, and Disease Prevention, School of Public Health, Loma Linda University, Loma Linda, CA, USA.
5
Alzheimer's Disease and Other Cognitive Disorders Unit, Neurology Service, Hospital Clínic, IDIBAPS, Barcelona, Spain.
6
Department of Psychology, School of Behavioral Health, Loma Linda University, Loma Linda, CA, USA.
7
Department of Preventive Medicine and Public Health, School of Medicine, University of Valencia, Valencia, Spain.
8
Department of Medicine, Faculty of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, IDIBAPS, Barcelona, Spain.
9
Department of Biomedicine, Faculty of Medicine and Health Sciences, University of Barcelona, Barcelona, Spain.

Abstract

BACKGROUND:

Walnut consumption counteracts oxidative stress and inflammation, 2 drivers of cognitive decline. Clinical data concerning effects on cognition are lacking.

OBJECTIVES:

The Walnuts And Healthy Aging study is a 2-center (Barcelona, Spain; Loma Linda, CA) randomized controlled trial examining the cognitive effects of a 2-y walnut intervention in cognitively healthy elders.

METHODS:

We randomly allocated 708 free-living elders (63-79 y, 68% women) to a diet enriched with walnuts at ∼15% energy (30-60 g/d) or a control diet (abstention from walnuts). We administered a comprehensive neurocognitive test battery at baseline and 2 y. Change in the global cognition composite was the primary outcome. We performed repeated structural and functional brain MRI in 108 Barcelona participants.

RESULTS:

A total of 636 participants completed the intervention. Besides differences in nutrient intake, participants from Barcelona smoked more, were less educated, and had lower baseline neuropsychological test scores than those from Loma Linda. Walnuts were well tolerated and compliance was good. Modified intention-to-treat analyses (n = 657) uncovered no between-group differences in the global cognitive composite, with mean changes of -0.072 (95% CI: -0.100, -0.043) in the walnut diet group and -0.086 (95% CI: -0.115, -0.057) in the control diet group (P = 0.491). Post hoc analyses revealed significant differences in the Barcelona cohort, with unadjusted changes of -0.037 (95% CI: -0.077, 0.002) in the walnut group and -0.097 (95% CI: -0.137, -0.057) in controls (P = 0.040). Results of brain fMRI in a subset of Barcelona participants indicated greater functional network recruitment in a working memory task in controls.

CONCLUSIONS:

Walnut supplementation for 2 y had no effect on cognition in healthy elders. However, brain fMRI and post hoc analyses by site suggest that walnuts might delay cognitive decline in subgroups at higher risk. These encouraging but inconclusive results warrant further investigation, particularly targeting disadvantaged populations, in whom greatest benefit could be expected.This trial was registered at clinicaltrials.gov as NCT01634841.

KEYWORDS:

cognition; neuroimaging; nuts; omega-3; α-linolenic acid

PMID:
31912155
DOI:
10.1093/ajcn/nqz328

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