The new study suggests that the impact of obesity is nuanced and related more to specific body composition rather than weight alone.
“We consistently observed an increased risk with ‘central obesity’ [characterized by fat mass mainly in the torso] and ‘arm-dominant fat distribution’ patterns, and a reduced risk with the ‘muscle strength’ pattern, in both clinical neurodegenerative disease onset and brain aging markers,” says lead study author Shishi Xu, MD, a researcher with the department of endocrinology and metabolism at Sichuan University’s West China Biomedical Big Data Center in Chengdu.
“This confirmed our hypothesis that it is not the absolute weight of fat and muscle, but their distribution and quality that significantly impact the development of neurodegenerative diseases.”
Body Composition Makes a Difference
For the analysis, Dr. Xu and her colleagues examined health data from more than 400,000 people, average age 56. Free of neurodegenerative diseases at study start, participants were measured for specific body composition elements, such as waist and hip size, grip strength, bone density, and fat and lean mass.
During an average of nine years of follow-up, about 8,200 subjects (about 2 percent) developed neurodegenerative diseases — mainly Alzheimer’s disease, other dementia-causing diseases, and Parkinson’s disease.
After adjusting for other factors that could influence the rate of these disorders (such as high blood pressure, smoking and drinking status and diabetes), the investigative team calculated that adults with high levels of belly fat were 13 percent more likely to develop these diseases compared with adults with low levels of belly fat.
Also, participants with high levels of arm fat were 18 percent more likely to develop the diseases than those with low levels of arm fat.
Muscular power, on the other hand, was shown to have a protective effect. Those with high muscle strength were 26 percent less likely to develop the diseases than those with low levels of strength.
How Fat and Muscle Play a Role
Yuko Hara, PhD, director of aging and Alzheimer’s prevention at the Alzheimer’s Drug Discovery Foundation, offers a possible explanation for these findings. (Dr. Hara was not involved in the current research.)
Because frailty is also among the top contributors to neurodegenerative decline, Joel Salinas, MD, clinical assistant professor of neurology at NYU Langone Health in New York City and chief medical officer at Isaac Health, advises that building up muscle makes sense as a way to possibly ward off dementia.
“Muscle strength is associated with better physical fitness and metabolic health, which can reduce inflammation and improve cardiovascular function,” says Dr. Salinas, who was not involved in the research.
People with high levels of arm fat are likely to have less arm muscle mass, and that is associated with not getting enough physical activity, which is yet another risk factor for dementia.
Lifestyle Changes Can Cut Risks
Because the analysis was not based on direct clinical trials, study authors point out that more evidence is needed to clarify whether these body composition factors are just early risk indicators or really a possible cause of neurodegenerative diseases.
Still, the research may help people who want to understand their risk of developing Alzheimer’s and Parkinson’s. That can be motivation to make positive lifestyle changes that can change body composition and build muscle strength.
“In recent years, due to the widespread use and even abuse of weight loss drugs such as semaglutide, people have become overly concerned with overall weight and often overlook the key role of different body compositions,” says Xu. “We want to emphasize that the quality or distribution of your muscle and adiposity [accumulation of fat], rather than the absolute weight, may be more important for your health.”
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