A study of older adults in China found that people with higher estimated body fat were less likely to develop Alzheimer’s-type mild cognitive impairment (MCI) or dementia during an average follow-up of 2.27 years.
The findings describe an association, not proof that body fat protects against Alzheimer’s disease. The researchers also cautioned that the results do not support gaining body fat to prevent dementia.
What the study found
The observational study followed 2,349 dementia-free adults enrolled through the Hubei Memory and Aging Cohort Study. Participants lived in the community, were recruited at seven research centers in Hubei Province between 2018 and 2023, and had an average age of 71.9. The group included 1,070 men and 1,279 women.
Compared with people in the lowest quarter of estimated body fat, those in the highest quarter had:
- A hazard ratio of 0.52 for Alzheimer’s-type MCI, with a 95% confidence interval of 0.36 to 0.76.
- A hazard ratio of 0.59 for Alzheimer’s-type dementia, with a 95% confidence interval of 0.39 to 0.89.
In absolute terms, Alzheimer’s-type MCI developed in 46 of 359 people in the highest body-fat quarter and 77 of 323 in the lowest quarter. Alzheimer’s-type dementia developed in 37 of 586 people in the highest quarter and 67 of 587 in the lowest quarter.
When the analysis accounted for competing risks from other causes of decline, the estimate for Alzheimer’s-type dementia changed to 0.68, with a confidence interval of 0.45 to 1.03. That wider interval included the possibility of no clear difference, making the dementia finding less certain.
The measurement was an estimate, not a body-fat scan
Researchers estimated body fat with CUN-BAE, a calculation based on body mass index, age and sex. The measure has been compared with DEXA scans, but it does not directly measure body fat, distinguish fat from muscle or show where fat is distributed in the body.
Analyses accounted for age, education, high blood pressure and diabetes. In the Hubei cohort, Alzheimer’s-type MCI and dementia were classified from clinical patterns, including gradual onset and steadily worsening memory or thinking, rather than biomarker testing.
The association was not clear for MCI or dementia attributed to causes other than Alzheimer’s disease. The hazard ratio was 0.95 for MCI from other causes and 0.71 for dementia from other causes, with confidence intervals that did not establish a clear difference.
Age, sex and disease stage
Among participants who had normal cognition at the start, each one-point increase in estimated body-fat percentage was associated with a relative risk ratio of 0.91 for developing MCI. The association was statistically significant only among people aged 70 to 74; estimates were 0.95 for ages 65 to 69 and 0.97 for those aged 75 and older.
Among people who already had MCI at the beginning, changes in body fat were not linked to recovery or progression to dementia.
Formal tests did not find significant differences in the results by sex or age. The study’s subgroup findings were exploratory, so the suggested patterns should not be treated as established differences between men and women or between age groups.
What the validation data showed
The researchers also examined 1,858 dementia-free participants from the Alzheimer’s Disease Neuroimaging Initiative, a mostly North American research cohort that included brain scans and spinal fluid tests.
In that cohort, each one-point increase in estimated body fat was associated with lower odds of testing positive for both amyloid and tau in men and women. The odds ratio was 0.91 for men and 0.93 for women. Higher estimated body fat was also linked to less amyloid across multiple brain regions, with larger effects in women.
Some additional patterns were more limited. Higher estimated body fat was linked to lower blood p-tau217 in women and, above about 37.6% estimated body fat, to higher blood amyloid-beta 42. A link with less tau appeared only in men with MCI, mainly among those who were already amyloid-positive. The researchers described the overall pattern as a hypothesis for future testing, not a confirmed sex difference, because formal interaction tests were not significant.
Why the result needs careful interpretation
Because the study was observational, it cannot determine whether body fat caused the lower rate of Alzheimer’s-type outcomes. The follow-up was also short enough that it could not rule out reverse causation: weight loss may occur during the early stages of an undiagnosed disease.
Deaths could not be modeled. The source also notes that older adults with higher body fat who survived to later ages may represent an unusually healthy group of survivors. This could influence the observed association.
The results do not overturn the established health concerns associated with obesity, including heart and metabolic risks. Nor do they establish that body-fat percentage is a treatment target or a reliable standalone way to predict dementia. Unplanned weight loss in later life can precede memory problems and is a change worth discussing with a doctor.
Key takeaways
- In a 2,349-person observational study, higher estimated body fat was associated with lower rates of Alzheimer’s-type MCI and dementia over an average of 2.27 years.
- The highest body-fat quarter had hazard ratios of 0.52 for Alzheimer’s-type MCI and 0.59 for Alzheimer’s-type dementia compared with the lowest quarter.
- The body-fat measure was calculated from BMI, age and sex rather than directly measured, and it did not show fat distribution.
- The association does not prove that body fat protects against Alzheimer’s disease or support gaining body fat to prevent dementia.
What this means
The study is relevant because it challenges a simple assumption that higher body weight always corresponds to higher dementia risk, but it does not provide a reason to pursue weight gain. Body composition, changes in weight over time, cardiovascular and metabolic health, and the underlying causes of cognitive change are not captured by a single estimated body-fat percentage. Unexpected weight loss in an older adult can occur before memory problems and is a change to discuss with a doctor.
What the evidence cannot tell us
- The study was observational and cannot establish that body fat caused the lower risk.
- The average 2.27-year follow-up was short and could not rule out weight loss caused by early, undiagnosed disease.
- CUN-BAE estimated body fat from BMI, age and sex; it did not directly measure fat, distinguish fat from muscle or indicate fat distribution.
- Hubei clinical classifications of Alzheimer’s-type MCI and dementia were based on symptoms without biomarker confirmation when participants were classified in that cohort.
AI tools were used to assist with the preparation of this article under our editorial standards.
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