Previous research has found that unexplained weight loss is an early sign of Alzheimer's. Now a study involving 140 older adults (60+), of whom half had early-stage Alzheimer's disease, has revealed that it is not the overall weight or fat levels that are important, but the loss of lean mass (weight of an individual's bones, muscles and organs without body fat). This directly correlated with reductions in the volume of the whole brain and of white matter only, along with declines in cognitive performance. The finding is consistent with research suggesting that brain pathology contributes to a decline in body composition, perhaps by disrupting the regulation of energy metabolism and food intake, perhaps through behavioral changes (there is a strong association between loss of muscle mass and reductions in physical activity), or perhaps through a common underlying mechanism, such as inflammation.
(2010). Reduced Lean Mass in Early Alzheimer Disease and Its Association With Brain Atrophy.
Arch Neurol. 67(4), 428 - 433.