“Healthier bodies with more muscle mass and less hidden belly fat are more likely to have healthier, youthful brains,” said senior study author Cyrus Raji, M.D., Ph.D., associate professor of radiology and neurology in the Department of Radiology at Mallinckrodt Institute of Radiology at Washington University School of Medicine in St. Louis, Missouri. “Better brain health, in turn, lowers the risk for future brain diseases, such as Alzheimer’s.”

How MRI Measures Brain Age and Body Composition

Brain age is an estimate of how old the brain appears biologically, based on its structure as seen through MRI. Body MRI can track muscle mass, which serves as a marker for efforts to reduce frailty and strengthen overall health. Estimated brain age from structural scans may also shed light on risk factors for Alzheimer’s disease, including muscle loss.

“While it is commonly known that chronological aging translates to loss of muscle mass and increased hidden belly fat, this work shows that these health measures relate to brain aging itself,” Dr. Raji said. “It shows muscle and fat mass quantified in the body are key reflectors of brain health, as tracked with brain aging.”

Study Details: Imaging, AI Analysis, and Participant Profile

The study evaluated 1,164 healthy adults (52% women) across four research sites using whole-body MRI. Participants had a mean chronological age of 55.17 years. Imaging included T1-weighted MRI sequences, which highlight fat as bright and fluid as dark, providing a clear view of muscle, fat, and brain tissue. An artificial intelligence (AI) algorithm measured total normalized muscle volume, visceral fat (hidden belly fat), subcutaneous fat (fat under the skin) and predicted brain age.

The data indicated that individuals with a higher visceral fat to muscle ratio had higher predicted brain age. Subcutaneous fat showed no meaningful association with how old the brain appeared.

“The participants with more muscle tended to have younger-looking brains, while those with more hidden belly fat relative to their muscle had older-looking brains,” Dr. Raji said. “The fat just under the skin wasn’t related to brain aging. In short, more muscle and a lower visceral fat to muscle ratio were linked to a younger brain.”

Implications for Health, Prevention, and Future Interventions

Dr. Raji explained that focusing on building muscle and reducing visceral fat are realistic and actionable goals. Whole-body MRI and AI-based brain age estimates can offer clear benchmarks for programs designed to lower visceral fat while maintaining or increasing muscle.

He also noted that the results highlight the close connection between physical health and brain health.

“This research has validated widely held hypotheses about the association between body composition biomarkers and brain health and provides a foundation for those biomarkers to be included in future trials of various metabolic interventions and treatments,” he said.

What the Findings Mean for GLP-1 Weight Loss Drugs

Commonly prescribed glucagon-like peptide-1 (GLP-1) weight loss medications, including Ozempic, are effective at reducing body fat but may also contribute to muscle loss. Dr. Raji suggested that the study’s findings could help guide the development of next-generation therapies. These future treatments may aim to reduce visceral fat more than subcutaneous fat while protecting muscle mass.

“Losing fat — especially visceral fat — while preserving muscle volume would have the best benefit on brain aging and brain health based on insights from our work,” he said. “Thus, our study can inform future treatments by promoting research that quantifies MRI of body fat, muscle and brain age, which can help determine the optimal dosing regimens for GLP-1s to achieve the best outcomes in body and brain health.”

Co-authors are Somayeh Meysami, M.D., Soojin Lee, Ph.D., Saurabh Garg, M.Sc., Nasrin Akbari, M.Sc., Rodrigo Solis Pompa M.D., M.H.Sc., Ahmed Gouda, M.Sc., Thanh Duc Nguyen, Ph.D., Saqib Abdullah Basar, M.B.B.S., M.P.H., Yosef G. Chodakiewitz, M.D., David A. Merrill, M.D., Ph.D., Alex Exuzides, Ph.D., M.D., Amar P. Patel, M.D., Daniel J. Durand, M.D., M.B.A., and Sam Hashemi, M.Sc.

Earthquakes have the potential to reshape this environment in several ways. Shaking can break open new rock surfaces, force out fluids that were previously sealed away, and redirect the flow of water through the subsurface. Each of these effects can create fresh chemical reactions, which in turn alter the types of energy available to microbial communities. The authors refer to this shift in available resources as a change in the chemical “menu” that microbes can draw from.

Sampling Yellowstone’s Deep Fluids After the Quake Swarm

To understand how seismic activity influenced this hidden ecosystem, the researchers collected water samples from a nearly 100-meter deep borehole located along the western edge of Yellowstone Lake. They sampled the site five times throughout 2021, giving them a rare look at how conditions changed both immediately and over the following months.

Analyses of these samples showed notable increases in hydrogen, sulfide, and dissolved organic carbon after the earthquakes. These compounds serve as important energy sources for many subsurface organisms. As the chemistry of the water shifted, the team also detected a rise in planktonic cells, suggesting that more microbes were present in the water column than before. This combination of chemical and biological changes indicates that the quake swarm temporarily boosted the resources available to deep microbial life.

Microbial Communities in Motion

Beyond detecting an increase in cell numbers, Boyd and colleagues observed that the types of microbes present changed over time. This result stands out because subsurface microbial communities in continental bedrock aquifers are often considered relatively stable. In contrast, the Yellowstone system appeared to respond quickly and noticeably to the pulse of seismic energy.

According to the authors, the kinetic energy associated with earthquakes can influence both the chemistry and the biological makeup of aquifer fluids. Their findings imply that even small seismic events can drive meaningful ecological shifts underground.

Implications for Other Worlds With Rock and Water

The processes observed in the Yellowstone borehole may not be unique. Many regions around the world experience regular seismic activity that could similarly reshape subsurface energy supplies. If this mechanism is widespread, it could help explain how microbial life persists in deep and isolated environments.

The team also notes that the same basic dynamics might occur on other rocky planets that contain water. If earthquakes or similar geological motions can refresh chemical resources below the surface, this could expand the possible habitats for microbes on worlds such as Mars.