Distinct associations between body mass index and polyunsaturated fatty acids in dementia with Lewy Bodies and Alzheimer’s disease

Objective We aimed to assess the association between body mass index and polyunsaturated fatty acids to determine potential links and metabolic differences between Alzheimer's disease and dementia with Lewy bodies. Methods We performed a cross-sectional study of enrolment data with 133 patients with mild AD (n = 75) and DLB (n = 58) from a Norwegian cohort study. We used linear regression models adjusting for age, sex, and diagnosis to explore the association between PUFA concentrations and BMI estimates. Results In DLB patients, BMI was positively associated with downstream omega-6 PUFA, including gamma-linolenic acid (GLA; β = 0.285, p = 0.012), arachidonic acid (AA; β = 0.320, p = 0.005), and adrenic acid (β = 0.303, p = 0.005). BMI was also related to increased Δ6-desaturase n-6 activity (β = 0.383, p = 0.002) and Δ6-desaturase n-3 activity (β = 0.335, p = 0.011), along with reduced elongase n-6 (β = –0.396, p = 0.002) and elongase n-3 (β = –0.376, p = 0.004), suggesting increased fatty acid turnover. No significant associations were found in the AD group. Conclusions BMI in DLB patients was positively associated with elevated downstream omega-6 metabolites and desaturase and elongase activity, compatible with higher fatty‑acid turnover and systemic inflammatory state hypothesized in DLB. These findings highlight the distinct metabolic alterations across dementia subtypes that are relevant for personalized nutritional strategies in dementia care.