Weight loss is a common but puzzling problem for many people living with Parkinson’s disease. Patients often become thinner as the disease progresses, even when they are eating enough food.
For years, doctors were unsure whether this weight loss was caused by muscle wasting, poor nutrition, or other hidden changes in the body.
A new study now suggests a surprising explanation: the body is losing fat, not muscle, and shifting into a different way of producing energy.
The research, published in the Journal of Neurology, Neurosurgery & Psychiatry, was led by scientists at Fujita Health University in Japan. The team studied 91 people with Parkinson’s disease and compared them with 47 healthy adults.
They measured body composition to see how much fat and muscle each person had, and they analyzed blood samples to understand how the body was producing energy.
The results showed that people with Parkinson’s weighed less mainly because they had lost body fat. Their muscle mass was largely preserved, especially in the earlier stages of the disease.
This finding challenges the common belief that weight loss in Parkinson’s is mainly due to muscle decline.
More importantly, the researchers discovered that this fat loss is linked to a deeper problem with how the body makes energy.
Normally, the body turns glucose from food into energy through a process that acts like its main power system.
In Parkinson’s patients, this system appeared to be weakened. Key substances involved in energy production were lower than normal, suggesting that the body could no longer efficiently convert sugar into usable fuel.
When the main energy system fails, the body activates a backup plan. Instead of relying on carbohydrates, it begins breaking down fat — and sometimes protein — to produce energy.
This process creates molecules called ketone bodies, which were found at higher levels in the patients, especially in those who were thinner or had more advanced disease.
In simple terms, the body appears to switch into an “emergency mode” to survive when its usual energy supply stops working properly.
Researchers say this hidden energy crisis may explain why simply eating more calories does not always prevent weight loss in Parkinson’s disease. If the body cannot use glucose efficiently, extra food alone may not solve the problem.
The findings could change how doctors approach care for Parkinson’s patients. Instead of focusing only on increasing calorie intake, future treatments might aim to support the body’s energy-producing systems or protect mitochondrial function, which plays a key role in generating energy inside cells.
The study also highlights that Parkinson’s disease affects more than movement and the brain. It can disrupt basic body processes such as metabolism. Recognizing unexplained weight loss as a warning sign of these deeper changes could help doctors identify patients at higher risk and intervene earlier.
By revealing that Parkinson’s disease pushes the body to burn fat for survival rather than maintaining its normal energy production, the research offers a new way of understanding the disease — and new hope for better treatments in the future.
