'The Rear View: How Glute Shape Predicts Diabetes Risk'

 Thanks to imaging data, researchers may have a new perspective on type 2 diabetes (T2D) risk — from the backside.

Researchers in the UK used three-dimensional MRI to study how age-related changes in the shape of a person’s gluteus maximus (GM) muscle were associated with an increase in T2D risk over time, and the results differed by sex.

“There is growing interest in the central role of muscle in lifelong health, from age-related conditions, such as sarcopenia and frailty, to metabolic diseases, especially at a time when many people are concerned about potential muscle loss associated with weight-loss drugs,” Louise Thomas, PhD, professor of metabolic imaging at the University of Westminster, London, England, told Medscape Medical News.

“We wanted to understand whether muscle shape also carries important information, beyond the traditional measures of muscle volume and quality,” she said, adding that muscle quality is defined as the amount of fat infiltration.

Assessing GM Morphology

In a study presented at the Radiological Society of North America 2025 Annual Meeting, Thomas and colleagues reviewed data from 61,290 MRI exams in the UK Biobank database. They combined the imaging with data on physical measurements, demographics, disease biomarkers, medical history, and lifestyle factors to explore how sex-specific GM morphology related to body measures and T2D.

GM shape was defined in terms of surface-to-surface (S2S) imaging, a technique often used in assessment of internal organs that compares the differences between a patient’s anatomical surface and reference model templates for adult men and adult women. Positive values define muscle expansion, and negative values define muscle shrinkage or atrophy.

Overall, a rounder GM was significantly associated with higher BMI, greater alcohol intake, more physical activity, and increased grip strength, while those with flatter GMs were more likely to be older and frailer and more likely to have osteoporosis and spend more time sitting (P < .05 for both).

However, in men, T2D was significantly associated with a flatter bottom, while the opposite was true for women (P < .05 for both). The negative median difference in S2S from the template was -0.41 mm and -0.39 mm on the right and left GM muscles, respectively, for men with T2D, suggesting atrophy. For women, the positive median differences of 0.45 mm and 0.49 mm for the right and left GM muscles, respectively, suggested fatty hypertrophy, according to the researchers.

Sex Differences Surprising

“We were surprised not just by the scale of the differences, but by how sharply the muscle shape patterns linked to type 2 diabetes diverged between men and women,” Thomas told Medscape Medical News. “Men showed clear regions of localized thinning consistent with muscle atrophy, whereas women showed outward bulging that likely reflects increased fat deposition,” she explained.

“We also found that people with a larger gluteus maximus at baseline had a substantially lower future risk of developing type 2 diabetes, even after accounting for age, BMI, waist-to-hip ratio, physical activity, and other lifestyle factors,” she said.

The results suggest different biological responses to the same disease, she noted. Not surprisingly, individuals with higher fitness, as measured by vigorous physical activity and hand grip strength, also had a rounder GM shape, while aging, frailty, and long sitting times were linked to muscle thinning, Thomas said.

The findings were limited by providing only a single snapshot measure, but the large study population makes the results valuable for understanding muscle structure at scale, said Thomas.

“Crucially, UK Biobank is now conducting repeat scans in another 60,000 participants, due to complete by 2030, and this follow-up will give us the opportunity to track how muscle shape changes as people age or modify their lifestyle,” she added. Sex-specific GM shape changes in T2D may reflect local differences in response to insulin tolerance that merit additional investigation, she said.

Spatial Specificity Unexpected

The new study addresses a key limitation in how muscle health is assessed in metabolic disease, said Ricardo Rosero-Revelo, MD, endocrinologist at the Cleveland Clinic, Cleveland, and lead author of a study describing a predictive model for muscle mass loss in obesity.

“Traditional metrics such as muscle volume or total fat measures miss regional, sex-specific muscle adaptations that may be clinically meaningful,” said Rosero-Revelo, who was not involved in the UK study. “The availability of large biobank MRI datasets combined with automated segmentation and shape modeling allow for population-scale mapping of subtle morphological changes,” he said. The researchers leveraged these tools to refine muscle phenotyping in T2D in a way that was not previously feasible, he added.

While the findings were biologically plausible, the spatial specificity was surprising, Rosero-Revelo told Medscape Medical News.

“Sex differences in fat distribution and muscle aging are well described, which makes divergent patterns between men and women in type 2 diabetes reasonable; however, it was unexpected to see clearly localized regions of inward versus outward deformation rather than a uniform change in muscle size,” he said.

“This highlights that metabolic disease affects skeletal muscle heterogeneously and supports the idea that muscle phenotype, not just muscle quantity, matters,” he explained.

Consider Muscle Mass in Clinical Care

The key implication for clinical practice is that relying on BMI, body weight, or even muscle quantity alone is insufficient to understand muscle health in people with T2D, Rosero-Revelo said. “While MRI-based shape analysis is not feasible for routine care, the study reinforces a practical direction for clinicians to incorporate scalable tools, such as body composition assessment together with strength and functional testing, to better approximate muscle quality and detect ‘hidden’ muscle vulnerability,” he said.

“Much of the clinical messaging around health focuses on weight loss and body fat, and while that matters, maintaining healthy muscle mass is just as essential for long-term well-being,” Thomas added.

“We should be encouraging people to engage in simple resistance exercises that help strengthen, build, and preserve muscle; this message deserves far more prominence in public health conversations,” she said.

Limitations of the study include reliance on MRI-based shape analysis, which is resource-intensive and not readily scalable, as well as potential selection bias, because only participants with high-quality imaging and valid segmentations can be included, Rosero-Revelo said. The study’s cross-sectional design prevents conclusions of causality, and the results may not generalize to all populations, he added.

“Future research should include longitudinal and multiethnic validation, calibration against reference measures of muscle composition and function, and development of simpler surrogate markers that can capture similar phenotypes in routine clinical practice,” said Rosero-Revelo.

“In the longer term, improved assessment of muscle health could inform treatment personalization, including selecting and monitoring therapies with attention to preserving lean tissue during weight loss,” he said.

The study reported receiving no outside funding. The researchers and Rosero-Revelo reported having no financial conflicts to disclose.

https://www.medscape.com/viewarticle/rear-view-how-glute-shape-predicts-diabetes-risk-2026a10002pk