Waist size carried a stronger cognitive signal than BMI in a Dutch cohort
In 3,873 middle-aged adults followed with repeated testing, waist-based categories of overweight and obesity showed larger effect sizes than BMI-based ones. The link to actual decline appeared only in men.
Body mass index is the number that decides who counts as having obesity, who qualifies for treatment, and what public health targets are measured against. It is also a ratio of weight to height that says nothing about where the weight sits. A Dutch cohort analysis published this month provides a small, specific piece of evidence on what that omission costs.
Researchers analysed 3,873 participants from the Doetinchem Cohort Study, aged 45 to 70 at baseline and 52% women, with up to six repeated rounds of measurement [s1]. At each round they recorded body mass index and waist circumference, and administered cognitive tests scored into four domains: global cognition, memory, flexibility, and processing speed [s1].
Participants were classified as having obesity at a BMI of 30 kg/m² or above, and as having abdominal obesity at a waist circumference of 102 cm or more in men and 88 cm or more in women [s1].
What was found
Higher BMI and higher waist circumference were both associated with worse cognitive performance across all four domains [s1]. That much is consistent with a large existing literature and is not the interesting part.
The interesting part is the comparison. When the two measures were used as categories — overweight or obesity, yes or no — the effect sizes attached to the waist-based categories were generally larger than those attached to the BMI-based categories [s1]. Having obesity by either definition, compared with a healthy BMI or waist, was consistently associated with worse memory in both sexes [s1].
The pattern of which domain moved most also differed by measure. For BMI the smallest difference was in global cognition and the largest in flexibility; for waist circumference the smallest was in processing speed and the largest in memory [s1].
Level versus decline
The study separates two questions that are easy to conflate: whether people with more adiposity perform worse at a given moment, and whether they lose ground faster over time. The first was true for both sexes and both measures. The second was not.
Associations with accelerated cognitive decline appeared only in men [s1]. In men, abdominal obesity was associated with faster decline in processing speed at all ages, and with faster decline in global cognition and flexibility among those older than 55 at baseline [s1]. In women, the authors report no such associations with decline, and no modification by age [s1].
A sex difference of that shape has more than one possible explanation, and an observational cohort cannot distinguish between them. It could reflect biology. It could reflect that the waist threshold of 88 cm in women captures a different slice of the population than 102 cm does in men. It could reflect differences in the range of values or in statistical power. The study does not resolve this, and the authors do not claim it does.
What it does not show
This is an observational cohort, not a trial. Nothing here establishes that abdominal fat causes cognitive decline, or that reducing waist circumference would prevent it. Reverse causation is a live concern in this literature: early cognitive change can alter diet, activity, and weight years before it is measurable on a test.
The cohort is a single Dutch population sampled from one town, which limits how far the effect sizes travel. And cognitive test scores in a research setting are not diagnoses.
Why the measure matters anyway
The finding sits alongside a broader argument the obesity field has been having for several years: that BMI is a screening convenience rather than a description of disease, and that categories built on it may sort people into the wrong groups. This study does not settle that argument. It adds one data point in one direction — that when the same population was classified two ways, the waist-based classification tracked the outcome somewhat more closely [s1].
That is a modest claim, and it should be read as one. But it is the kind of comparison the field mostly does not run, because BMI is already in the record and waist circumference often is not.
This article is informational and is not medical advice.
Sources
- Association of body mass index, waist circumference, (abdominal) overweight and obesity with sex- and age-specific cognitive function over time — the Doetinchem Cohort Study — International Journal of Obesity, 2026-03-17
Sources
- Association of body mass index, waist circumference, (abdominal) overweight and obesity with sex- and age-specific cognitive function over time — the Doetinchem Cohort Study — International Journal of Obesity , March 17, 2026
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