Obesity’s brain health risk may depend on where fat is stored

Obesity may impact brain health, depending on where fat is stored in the body, not just on total body fat. New research studying this effect offers insights into the specific risks of fat distribution patterns. 

Researchers at The Affiliated Hospital of Xuzhou Medical University in Xuzhou, China, used data from 25,997 individuals in the UK Biobank database, which includes medical imaging measurements alongside volunteers’ physical measurements, demographics, disease biomarkers, medical history, and answers to lifestyle questionnaires.

This allowed the team to compare brain health outcomes with patterns of body fat distribution in the observational study.

“Our work leveraged MRI’s ability to quantify fat in various body compartments, especially internal organs, to create a classification system that’s data-driven instead of subjective,” says study co-author Kai Liu, M.D., Ph.D., an associate professor at The Affiliated Hospital’s Department of Radiology.

“The data-driven classification unexpectedly discovered two previously undefined fat distribution types that deserve greater attention.”

Top two most risky fat storage areas

The study authors pinpointed two fat distribution types on MRI scans with the strongest association with negative brain and cognitive outcomes. A “pancreatic predominant” type had a significantly high concentration of fat in the pancreas compared to other areas of the body and a “skinny fat” type, with a high fat burden despite not fitting the typical patterns of high obesity.

Both profiles had the highest association with extensive gray matter atrophy, accelerated brain aging, cognitive decline, and increased risk of neurological disease.

MRI scans linked high pancreatic fat and skinny-fat profiles — excessive internal fat despite low overall weight — most strongly to cognitive decline and poor brain health.These risks affected men and women, with “nuanced variations” between the sexes, the authors highlight.

Individuals with “pancreatic-predominant” distribution patterns had a proton density fat fraction of around 30% in the pancreas. This MRI marker provides a precise estimation of fat concentration in tissue.

“This level is about two to three times higher than that of other fat distribution categories, and it can be up to six times higher than that of lean individuals with low overall fat,” explains Liu.

“Additionally, this group tends to have a higher BMI and overall body fat load.”

Notably, these individuals didn’t have significantly pronounced liver fat compared to those with other profiles. High pancreatic fat accompanied by relatively low liver fat emerges as a distinct, clinically overlooked phenotype, Liu highlights.

“In our daily radiology practice, we often diagnose ‘fatty liver,’” he says. “But from the perspectives of brain structure, cognitive impairment, and neurological disease risk, increased pancreatic fat should be recognized as a potentially higher-risk imaging phenotype than fatty liver.”

Burden of “skinny fat”

Individuals with “skinny fat” profiles showed the highest fat burden in nearly all areas except the liver and pancreas. Unlike a balanced “high obesity” profile, the researchers note “skinny fat” tends to be more concentrated around the abdomen.

“Most notably, this type does not fit the traditional image of a very obese person, as its actual average BMI ranks only fourth among all categories,” Liu explains. “The increase is perhaps more in fat proportion. Therefore, if one feature best summarizes this profile, I think it would be an elevated weight-to-muscle ratio, especially in male individuals.”

To see how fat distribution affects other areas of health, such as cardiovascular or metabolic health, Liu says that more research is needed to determine how these patterns could be related.

Understanding the risks associated with specific fat distribution patterns could enable health care providers to guide more personalized treatment for cognitive health and performance. As Liu explains: “Brain health is not just a matter of how much fat you have, but also where it goes.”

The findings are published in Radiology, the journal of the Radiological Society of North America.

In other recent findings, a separate paper uncovered that dementia may pose a greater risk for people with obesity and high blood pressure. The study analyzed data from participants in Denmark and the UK to pinpoint a link between higher body weight and the progressive brain disease.