The relationship between muscle mass and metabolic health may be more complicated than previously understood, according to a new study from Pennington Biomedical Research Center. Researchers found that where fat is stored in the body plays an important role in the relationship between fat-free mass and metabolic conditions, including metabolic syndrome and elevated blood sugar.
The study, “ Relationship between fat-free mass and metabolic syndrome is shaped by ectopic fat in a UK Biobank cohort ,” published in The Journal of Clinical Endocrinology & Metabolism , analyzed body composition and metabolic health data from 59,269 participants in the UK Biobank. Using dual-energy X-ray absorptiometry (DXA) and magnetic resonance imaging (MRI) data from UK Biobank, researchers examined how different measures of body composition were associated with metabolic syndrome and elevated blood sugar.
Fat-free mass is often used as an indirect measure of skeletal muscle mass because muscle makes up the largest proportion of fat-free mass in most adults and plays an important role in regulating blood sugar and responding to insulin. However, fat-free mass, a term often used interchangeably with lean body mass, refers to the body's nonfat components, including muscle, bones and organs. The study found that fat-free mass alone may not provide a complete picture of a person's metabolic health.
“The findings suggest that muscle quantity alone may not provide a complete picture of metabolic health and that where fat is stored in the body is an important part of the story,” said Dr. Sri Lakshmi S. Devarakonda, postdoctoral researcher and first author of the study.
Researchers examined several measures of fat-free mass and assessed the influence of visceral adiposity, or fat stored deep within the abdomen around internal organs, and fat infiltration within muscle tissue. They also investigated whether sex hormones influenced the relationships between body composition and metabolic health.
The results varied depending on how fat-free mass was expressed. Higher total fat-free mass and fat-free mass adjusted for height were associated with a greater prevalence of metabolic syndrome and elevated glycated hemoglobin, a marker of average blood sugar levels. However, a higher proportion of body weight made up of fat-free mass was associated with a lower prevalence of these outcomes.
Further analyses revealed that these findings do not mean that having more muscle or fat-free mass is harmful. Rather, they highlight the complexity of body composition and suggest that the relationship between fat-free mass and metabolic health cannot be understood without considering fat distribution.
“Our findings suggest that we need to look beyond the amount of fat-free mass a person has to better understand their metabolic health,” said Dr. Candida Rebello, Director of the Nutrition and Chronic Disease Laboratory . “Where fat is stored in the body matters, particularly fat around internal organs and fat that accumulates within muscle tissue. These different patterns of fat distribution can influence the relationship between fat-free mass and metabolic risk, underscoring the importance of considering the quality and composition of body tissues, not just their quantity, when studying metabolic health.”
By combining body composition measurements from DXA and MRI with metabolic health data, the researchers were able to examine how the quantity and distribution of fat influence the relationship between fat-free mass and metabolic risk. The findings may help guide future research into how body composition can be better understood when assessing metabolic health.
The study, “Relationship between fat-free mass and metabolic syndrome is shaped by ectopic fat in a UK Biobank cohort,” was authored by Sri Lakshmi S. Devarakonda, Dachuan Zhang, Reilly Roberts and Candida Rebello of Pennington Biomedical Research Center.
About LSU's Pennington Biomedical Research Center
The Pennington Biomedical Research Center is at the forefront of medical discovery as it relates to understanding the triggers of obesity, diabetes, cardiovascular disease, cancer and dementia. Pennington Biomedical has the vision to lead the world in promoting nutrition and metabolic health and eliminating metabolic disease through scientific discoveries that create solutions from cells to society. The Center conducts basic, clinical and population research, and is a campus in the LSU System.
The research enterprise at Pennington Biomedical includes over 600 employees within a network of 44 clinics and research laboratories, and 16 highly specialized core service facilities. Its scientists and physician-scientists are supported by research trainees, lab technicians, nurses, dietitians and other support personnel. Pennington Biomedical is a globally recognized state-of-the-art research institution in Baton Rouge, Louisiana.
The Journal of Clinical Endocrinology & Metabolism
Data/statistical analysis
People
Relationship between fat-free mass and metabolic syndrome is shaped by ectopic fat in a UK Biobank cohort
8-Oct-2026