A recent study reveals that individuals classified as “metabolically healthy obese”—those with a body mass index (BMI) of 25 kg/㎡ or higher and at most one metabolic syndrome indicator—may have a lower risk of developing Alzheimer’s disease compared to their metabolically unhealthy counterparts. 

“Since weight and metabolic syndrome can be managed through diet, exercise, and medication, maintaining metabolic health and proper weight may help prevent Alzheimer’s-related dementia,” said Professor Kang Sung-hoon of Korea University Guro Hospital’s neurology department, who led the study. 

Professor Kang, also head of the newly launched Alzheimer’s prevention center at Korea University Guro Hospital, said that this study, published in Alzheimer’s Research & Therapy in August, is the first to confirm the combined impact of obesity and metabolic syndrome on these markers globally.

The research explored the effects of BMI on Alzheimer’s and vascular markers in relation to metabolic health.

Together with Professor Seo Sang-won of Samsung Medical Center’s neurology department, the team examined the influence of body weight and metabolic syndrome on Alzheimer’s-related protein buildup and progression. They categorized 1,736 dementia-free Koreans aged 45 and older by BMI—underweight (BMI under 18.5 kg/㎡), normal weight, and obese (BMI 25 kg/㎡ or higher). Each group was then further divided into “metabolically healthy” and “metabolically unhealthy” based on the International Diabetes Federation’s definition of metabolic syndrome.

Metabolically healthy individuals met only one or none of the metabolic syndrome criteria (high blood pressure, high fasting glucose, high triglycerides, or low HDL cholesterol), excluding waist circumference. The researchers then analyzed participants' amyloid PET, brain MRI, and cognitive function test results.

The study found that the beta-amyloid positivity rate—a key Alzheimer’s marker—was highest among the underweight group (73.9 percent) and lowest in the obese group (37 percent), suggesting that obesity may reduce amyloid buildup. In the metabolically healthy obese group, beta-amyloid positivity was 29.6 percent, compared to 42.5 percent in the obese metabolic syndrome group, indicating that the protective effect of obesity on amyloid accumulation is present only in metabolically healthy individuals. 

Additionally, the metabolically healthy obese group showed greater hippocampal volume and better cognitive performance, with the slowest cognitive decline over time.