Researchers from Oxford University, University College London, and collaborating institutions across Germany, France, and the Netherlands, found that diet quality and waist-to-hip ratio during midlife are associated with brain connectivity and cognitive performance in later life. Examining data from the Whitehall II Study, a longitudinal cohort of British civil service workers, the team concluded that healthier diets and lower waist-to-hip ratio during midlife correlate with improved brain health in older age.

Global shifts in dietary habits have contributed to rising rates of obesity, cardiovascular disease, and diabetes, all of which are linked to an increased risk of dementia. Research into the relationship between diet, metabolic health, and brain function has primarily focused on individual nutrients, with fewer studies assessing overall diet quality and body fat distribution over extended periods.

Previous studies have suggested that midlife is a critical window for cognitive health interventions, yet long-term study evidence on diet and brain connectivity remains limited.

In the study, "Association of Diet and Waist-to-Hip Ratio With Brain Connectivity and Memory in Aging," published in JAMA Network Open, researchers conducted a cohort study using data from the Whitehall II Study at University College London and the Whitehall II Imaging Substudy at the University of Oxford. The study analysed longitudinal changes in diet quality and waist-to-hip ratio to assess their association with hippocampal connectivity and cognitive function in aging.

The cohort included 512 participants in the diet quality analysis and 664 in the waist-to-hip ratio analysis. Participants were drawn from the Whitehall II Imaging Study, a subset of the larger Whitehall II Study that has followed over 10,000 British civil service workers since 1985. Data collection for the imaging substudy took place between 2012 and 2016, with brain imaging and cognitive assessments performed at an average age of 70 years.

Researchers assessed diet quality using the Alternative Healthy Eating Index–2010 (AHEI-2010), a scoring system designed to evaluate overall dietary intake. Waist-to-hip ratio was measured at five time points over a 21-year period.

Structural and functional brain connectivity was assessed using diffusion tensor imaging (DTI) and resting-state functional magnetic resonance imaging (fMRI). Cognitive function was measured using tests of working memory, executive function, and fluency.

Higher AHEI-2010 scores in midlife and across middle to older age were associated with increased hippocampal functional connectivity to the occipital lobe and cerebellum. Higher diet quality was also linked to better white matter integrity, as indicated by higher fractional anisotropy and lower mean diffusivity in brain scans.

Healthier diet quality in midlife was associated with better working memory, executive function, and overall cognitive performance, with improvements in working memory and executive function partially explained by better white matter integrity.

Higher waist-to-hip ratio in midlife was associated with widespread decreases in white matter integrity. Higher waist-to-hip ratio correlated with increased mean diffusivity and radial diffusivity in major white matter tracts, including the cingulum and inferior longitudinal fasciculus, which are implicated in memory and executive function. Reduced fractional anisotropy in these regions was linked to poorer cognitive performance. Mediation analyses indicated that the association between waist-to-hip ratio and cognitive decline was partially explained by changes in white matter connectivity.

Findings suggest that diet quality and abdominal obesity in midlife are predictive of brain connectivity and cognitive function in later life.

In an invited commentary, "Midlife Dietary Quality and Body Composition Relevance for Brain Connectivity and Cognitive Performance in Later Life," published alongside the study in JAMA Network Open, Sharmili Edwin Thanarajah, MD, from Goethe University Frankfurt, contextualised the findings within the broader public health challenge of dementia prevention.

Public health challenges related to obesity and poor diet require systemic interventions beyond individual choices. Thanarajah pointed to the worsening global obesity rates, where approximately 43% of adults and 20% of children are overweight, as a barrier to implementing effective cognitive health strategies. Strategies focused solely on personal responsibility may not be sufficient if food environments continue to promote high-calorie, nutrient-poor diets.

Sex differences in dietary behavior and metabolism were identified as a key gap in the current study. With only 20% of participants being female, the study leaves questions about whether the observed diet-brain associations apply equally to women. Differences in body fat distribution, hormonal influences on metabolism, and potential variations in brain aging between sexes warrant further study.

Thanarajah also noted that while higher alcohol consumption was associated with poorer dietary quality in the cohort, its role as an independent factor in brain aging remains difficult to disentangle. Alcohol's effects on white matter integrity, vascular health, and inflammation could complicate interpretations of diet-related cognitive outcomes. Future studies may benefit from more detailed assessments of alcohol intake patterns in relation to both diet and brain function.

Longitudinal studies like this one suggest that dietary improvements in midlife may benefit brain structure and function decades later, yet demonstrating causality remains challenging. Thanarajah argues that intervention studies targeting diet and obesity during midlife are needed to confirm whether modifying these factors can directly alter brain aging trajectories.

More information: Daria E. A. Jensen et al, Association of Diet and Waist-to-Hip Ratio With Brain Connectivity and Memory in Aging, JAMA Network Open (2025). DOI: 10.1001/jamanetworkopen.2025.0171

Sharmili Edwin Thanarajah, Midlife Dietary Quality and Body Composition Relevance for Brain Connectivity and Cognitive Performance in Later Life, JAMA Network Open (2025). DOI: 10.1001/jamanetworkopen.2025.0181

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