"Belt and Memory": How Diet and Belly Fat Rewire the Brain by Age 70

Brain aging begins long before clinically noticeable memory and attention impairments. The hippocampus, a key site for episodic memory formation, and the white matter conduction network, which facilitates efficient information exchange between cortical and subcortical regions, are considered to be the most vulnerable to age-related and metabolic effects. Microstructural changes in white matter tracts (e.g., decreased FA and increased MD/RD as measured by diffusion tensor MRI) are associated with vascular injury, inflammation, demyelination, and impaired axonal integrity. Resting-state fMRI reflects the “coherence” of hippocampal involvement in distributed memory networks and visual-associative circuits.

Midlife lifestyle factors are thought to determine the trajectory of cognitive aging. Two of these, diet quality and abdominal obesity, are biologically plausible to influence the brain in different ways:

• Diets rich in vegetables, fruits, whole grains, fish, nuts and limited in sugars, trans fats and processed meats are associated with better cardiovascular and metabolic profiles, less chronic inflammation and oxidative stress. These systemic effects potentially support perfusion, metabolism and neuroplasticity, which may be reflected in the integrity of the white tracts and the functional integration of the hippocampus. The AHEI-2010 index, a validated integral measure of such “diet quality”, is widely used in epidemiology.
• Abdominal obesity, assessed by waist-to-hip ratio (WHR) or height-to-height ratio (WHtR), reflects excess visceral fat better than BMI. Visceral adipose tissue is metabolically active: it increases insulin resistance, dyslipidemia, proinflammatory cascades, and endothelial dysfunction. These mechanisms are associated with microcirculatory damage, white-medulla hyperintensity, and tract microstructure degradation, which in turn impairs working memory and executive functions.

Despite the growing number of works, the literature has several gaps:

1. there are few longitudinal studies that have repeatedly measured diet and anthropometry in midlife and then correlated them with multimodal brain measures (DTI and resting-state fMRI) and cognitive tests in old age;
2. trajectories of change (improvement/deterioration of diet, WHR dynamics) are rarely assessed, although they may be the most informative; (3) there is insufficient evidence on whether white matter indices act as mediators linking metabolic risk factors to cognitive outcomes.

The Whitehall II cohort, a long-term UK longitudinal study originally recruited from civil service workers, provides a unique opportunity to close these gaps: repeated measures of diet (via the AHEI-2010) and WHR across decades of midlife, followed by MRI (DTI and resting-state fMRI) and standardised cognitive tests around age 70. This allows:

1. to test whether dietary intake and quality improvements in midlife are associated with more coherent hippocampal connectivity and healthier white matter microstructure in old age;
2. to assess whether higher WHR in midlife is associated with diffuse white tract changes and worse cognitive outcomes;
3. to test the hypothesis that white matter partially mediates the association of abdominal obesity with cognitive function.

Thus, the study is based on the concept of an “intervention window” of 45–70 years, when modifiable factors—nutrition and fat distribution—can program the structural and functional architecture of the brain and, as a consequence, the long-term cognitive trajectory.

In the Whitehall II longitudinal project in the UK, people who ate better in midlife had a more coherent hippocampus (the brain’s memory hub) and healthier white matter tracts at age 70. And those who had a higher waist-to-hip ratio (WHR) in midlife – a measure of abdominal fat – later showed worse working memory and executive function. Part of this effect was due to changes in white matter (the microstructure of the brain’s wiring). The study was published in JAMA Network Open.

What was studied

• Who: Participants in the Whitehall II Imaging sub-study (mainly UK civil service employees).
  • Nutrition cohort: 512 individuals (average age ~48 at baseline; ~70 at MRI).
  • Waist/hip ratio (WHR) cohort: 664 individuals.
  • Men ~80%, average BMI about 26.
• When: Nutrition was assessed 3 times over 11 years (from ~48 to ~60 years), WHR - 5 times over 21 years (from ~48 to ~68). MRI and cognitive tests - around 70 years.
• How was it measured:
  • Diet quality: AHEI-2010 index (more vegetables, fruits, whole grains, fish/nuts; less sugar, trans fats and processed meats).
  • Abdominal fat: WHR (waist/hips).
  • Brain:
    • hippocampal functional connectivity (resting-state fMRI),
    • white matter microstructure (DTI: FA - "fiber ordering", higher - better; MD/RD/AD - diffusion, higher - worse).
  • Cognition: working memory, executive functions, verbal fluency, episodic memory.

Main results

Nutrition → hippocampus and white matter

• The best diet in midlife and its improvement over time are associated with:
  • higher connectivity of the hippocampus with occipital and cerebellar areas (clusters for the left hippocampus total ~9,176 mm³; P < 0.05),
  • healthier white matter microstructure: higher FA and lower MD/AD in a number of tracts (including the superior longitudinal fasciculus, optic radiation, frontal tracts).
  • ROI analysis showed an association between dietary improvement and AD in the fornix, a key memory tract (adjusted P = 0.02).
• On average, the AHEI did not change much across the group, but individual improvements correlated with higher-quality pathways—an important signal that even a modest dietary upgrade makes sense.

Abdominal fat → white matter and cognition

• Higher WHR in midlife is associated with looser white matter microstructure at age 70:
  • higher than MD and RD (affected up to 26% and 23% of the total white matter framework; P ≤0.001/0.05),
  • below FA (about 4.9% of the skeleton; P < 0.05), particularly in the cingulum and inferior longitudinal fasciculus (ILF)—tracts critical for memory and attention.
• The same high WHR was associated with worse outcomes for:
  • working memory (digit span),
  • executive functions (Trail Making, digit coding),
  • episodic memory and semantic fluency.
• Part of the WHR → worse test performance association was via white matter: global FA/RD/MD measures mediated the effect (a small but significant proportion).

Why is this important?

• The window of intervention is “those same 48–70 years.” Both the quality of the diet and central obesity during these years are imprinted on the connectivity of the hippocampus and the integrity of the white tracts, and therefore on tomorrow’s memory and attention management abilities.
• Not just "weight" - "where" weight. Waist/hips are more informative than BMI for brain risks: "excess" on the stomach is associated with broader changes in the conduction pathways.

What does this mean in practice?

If you are 45–70:

• Nutrition for brain growth:
  • half a plate - vegetables and fruits, whole grains daily, legumes 3-5 times a week, fish 1-2 times a week, nuts - in portions;
  • Minimize sugary drinks, ultra-processed snacks, processed meats; cook "olive-Mediterranean."
• Keep your “belt” under control: focus on WHtR ~0.5 (waist/height) as a simple home marker; for WHR, monitor the dynamics at least once every 6–12 months.
• Movement + sleep + stress: aerobic activity 150-300 min/week, 2 strength sessions, sleep hygiene and stress management - “boosters” of brain structures.

In the doctor's office:

• Add WHR/WHtR to your usual BMI; for the "apple" type of obesity, discuss nutrition and activity more actively.
• In middle-aged patients with a high WHR, the threshold for cognitive screening and control of risk factors (BP, lipids, glucose) is low.

Important Disclaimers

• This is an observational study: it shows associations, not causation.
• Nutrition - according to the frequency questionnaire (there are errors).
• The sample is predominantly male and white British - generalisability to other groups requires confirmation.
• Associations with hippocampal functional connectivity were local and small—requiring replication.

Conclusion

Eat better — the memory “wires” are stronger; the wider the waist — the worse the brain’s “cable management.” Whitehall II data suggest that it makes sense to invest in the quality of your diet and reducing abdominal fat precisely in middle age — then by 70+ there is a higher chance of preserving both the integrity of white matter and clarity of mind.