Quick Facts

• Scientists scanned 26,000 brains and found visceral fat-to-muscle ratio predicts brain aging better than BMI
• People with normal weight but high hidden belly fat showed accelerated cognitive decline
• Muscle mass protects brain health through chemical signals that influence brain tissue

Scientists analyzed brain scans from 26,000 adults and discovered that body composition predicts cognitive decline more accurately than body weight alone.

The study, published in Radiology, used MRI scans to map fat distribution across eight body areas in participants from the UK Biobank. Researchers found that people with higher visceral fat relative to muscle mass showed accelerated brain aging, even when their total weight appeared normal.

“Healthier bodies with more muscle mass and less hidden belly fat are more likely to have healthier, youthful brains,” said senior study author Dr. Cyrus Raji, associate professor of radiology and neurology at Washington University School of Medicine.

The research examined 1,164 healthy individuals with an average age of 55 years. Scientists used artificial intelligence to measure total muscle volume, visceral fat, and brain age from whole-body MRI scans.

Participants with more muscle showed younger-looking brains, while those with more hidden belly fat relative to muscle had older-looking brains. Subcutaneous fat under the skin showed no connection to brain aging.

The study identified a concerning “skinny-fat” phenomenon. People who appeared normal weight but carried high fat relative to muscle across multiple body areas also showed accelerated brain aging and cognitive decline.

“The participants with more muscle tended to have younger-looking brains,” Dr. Raji said. “The fat just under the skin wasn’t related to brain aging. More muscle and a lower visceral fat to muscle ratio were linked to a younger brain.”

The average brain age of study participants was 56.04 years, nearly one year older than their chronological age of 55.17 years.

Researchers identified six distinct fat distribution profiles that people naturally fall into, moving beyond crude measurements like BMI or waist circumference.

The findings have immediate implications for popular weight loss medications. GLP-1 drugs like Ozempic effectively reduce body fat but may also contribute to muscle loss.

“Losing fat—especially visceral fat—while preserving muscle volume would have the best benefit on brain aging and brain health,” Dr. Raji said.

The muscle-brain connection works through chemical signals. When people exercise, muscles release compounds that positively influence brain tissue and other organs.

“This is why individuals who perform regular exercise tend to have lower risk of cognitive decline, dementia, and Alzheimer’s,” said expert Glenn Gaesser.

The research suggests a shift from focusing solely on weight loss to body recomposition—maintaining or building muscle while managing visceral fat.

Whole-body MRI scans combined with AI brain-age estimates provide objective tools to design and monitor interventions that lower visceral fat while preserving muscle mass.

Read more: Scientists Scanned 26K Brains & Found This Metric Predicted Cognitive Decline