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Weight loss is a well-recognized but poorly understood non-motor feature of Parkinson’s disease (PD). Many patients progressively lose weight as the disease advances, often alongside worsening motor symptoms and quality of life. Until now, it was unclear whether this reflected muscle loss, poor nutrition, or deeper metabolic changes. New research shows that PD-related weight loss is driven mainly by a selective loss of body fat, while muscle mass is largely preserved, and is accompanied by a fundamental shift in how the body produces energy.

Although PD is classically viewed as a neurological disorder, increasing evidence points to widespread metabolic dysfunction. Patients often experience fatigue and nutritional decline, yet dietary advice has largely focused on boosting calories. The new findings challenge this conventional view, showing that weight loss in PD reflects a failure of the body’s standard energy-producing pathways rather than reduced food intake alone. The findings are published in the Journal of Neurology, Neurosurgery & Psychiatry.

The study was led by Professor Hirohisa Watanabe from the Department of Neurology at Fujita Health University, School of Medicine, Japan, along with Dr. Atsuhiro Higashi and Dr. Yasuaki Mizutani from Fujita Health University. The team aimed to clarify what exactly is lost when patients with PD lose weight and why the body is forced to change its energy strategy.