Body composition differences in older adults with and without Alzheimer's disease: A systematic review and meta-analysis of observational studies

Background Research on body composition and fat distribution in Alzheimer's disease (AD) has presented conflicting findings. Objective Compare body composition and anthropometric measurements in older adults with and without AD. Methods A systematic review and meta-analysis were conducted following Cochrane guidelines and PRISMA standards. MEDLINE, Embase, Scopus, LILACS, WPRIM, and the Spanish Bibliographic Index of Health Sciences were searched up to September 2024, considering observational studies that compared body composition between AD groups and controls. Outcomes included body fat percentage, body mass index (BMI), impedance, resistance, and reactance. The methodological quality and level of evidence were assessed using the Joanna Briggs Institute scale and GRADE, respectively. A random-effects meta-analysis model was used to calculate mean differences (MD). Results Fourteen studies involving 2761 older adults were included. Older adult women with AD showed a lower body fat percentage (p < 0.01; MD = -5.07) and BMI (p = 0.05; MD = -1.28) compared to controls. Older adult men with AD had higher impedance (p = 0.01; MD = 2.05), resistance (p = 0.02; MD = 45.10), and lower reactance (p = 0.03; MD = -2.05) compared to controls. No significant differences in body fat percentage or BMI were found between older adults with and without AD, regardless of gender. Conclusions Women with AD showed lower body fat percentage and BMI, while men with AD had higher impedance, resistance, and lower reactance. These factors should be included in geriatric assessments for AD patients, though further research is needed to understand their link to cognitive outcomes in AD.