Weight loss is a typical symptom of Parkinson’s disease (PD). However, nothing is known about when it begins, how it progresses, and whether there is a difference in lean or fat mass loss. For a study, researchers wanted to determine how body composition varies before and after a Parkinson’s disease diagnosis. Body composition was measured by dual-energy x-ray absorptiometry on an annual or biennial basis from year 1 to year 10 in the Health, Aging, and Body Composition research (n=3075; age range, 70–79 years). Each year, for each PD instance, they estimated the difference between their actual body composition measurements and the values they would have had if they had not acquired PD. They investigated the trend of change in body composition measurements before and after Parkinson’s disease diagnosis using linear mixed models with crossed random factors.

A cohort had a total of 80 patients with PD. They began to notice a decrease in total and fat mass around 6–7 years before diagnosis, compared to their predicted values, albeit the changes were not statistically significant until 3–5 years after diagnosis. The decrease was large and long-lasting, with statistically significant changes in total body mass (P=0.008), fat mass (P=0.001), and percentage fat (P=0.001). Lean mass, on the other hand, remained steady throughout the study (P=0.16). Fat mass loss accounted for 96% of the total body mass decreased in patients with PD.

They discovered continuous weight loss in patients with PD, mostly in fat mass, commencing a few years before diagnosis in a longitudinal study using objective markers of body composition.