The number on the scale may not capture the full picture of type 2 diabetes risk. A large observational study found that adults with both obesity and poor muscle health were more likely to develop the condition than people with obesity alone.
The study, published in Diabetes Care, followed nearly 480,000 UK Biobank participants who did not have diabetes when the research began. Participants with sarcopenic obesity, a combination of excess body fat and low muscle mass or strength, had the highest rate of type 2 diabetes during up to 14 years of follow-up.
Because the study was observational, it cannot show that low muscle mass or strength caused type 2 diabetes or that building muscle would prevent it. Diet, physical activity, existing health conditions and other factors may affect body fat, muscle health and diabetes risk at the same time.
“Most people know carrying excess weight can increase the risk of type 2 diabetes, but our findings show muscle health is also an important piece of the puzzle,” said lead author Zhongyang Guan, a doctoral candidate at Curtin University.
Researchers classified participants according to whether they had obesity, sarcopenia, both conditions or neither. Sarcopenia generally refers to low muscle mass, reduced strength or a combination of the two, although the specific measurements used in research may differ from a clinical diagnosis.
Over 10 years, nearly 15% of participants with sarcopenic obesity developed type 2 diabetes. That compared with about 11% of those with obesity alone and approximately 3% of those with neither obesity nor sarcopenia.
After accounting for other measured factors, participants with sarcopenic obesity were more than 3.5 times as likely to develop type 2 diabetes as those with neither condition.
The difference was smaller when researchers compared people with sarcopenic obesity directly with those who had obesity alone. The group with both conditions had a 19% higher relative risk of developing type 2 diabetes.
That comparison helps put the headline figure in context. Much of the elevated risk was associated with obesity, but lower muscle mass or strength appeared to identify additional risk beyond obesity alone.
“People with both excess body fat and low muscle mass had a substantially higher risk of developing type 2 diabetes than those with obesity alone,” Guan said.
Muscle plays an important role in blood sugar regulation because it uses glucose for energy. Physical activity also helps muscle cells respond to insulin, the hormone that moves glucose from the blood into cells.
That biological connection makes the results plausible, but the study did not determine why participants with sarcopenic obesity developed type 2 diabetes more often. Low physical activity, poorer diet quality, chronic illness, inflammation or metabolic changes that precede diabetes could all contribute to both declining muscle health and rising blood sugar.
The study also did not test resistance training, protein intake, weight loss or any other prevention strategy. It therefore cannot tell readers how much muscle they would need to gain, whether increasing strength would change their risk or whether muscle mass matters more than muscle function.
“The more muscle we have and the more regularly we use them, the better equipped our body is to prevent or manage type 2 diabetes,” said Jessica Weiss, clinical services manager for Diabetes WA.
Regular physical activity is already recommended as part of type 2 diabetes prevention and management. Still, the idea that more muscle is always better would be an oversimplification. Muscle strength, quality, activity and metabolic function may all matter, and a person’s appearance does not reliably show how healthy their muscle tissue is.
The association between sarcopenic obesity and type 2 diabetes was particularly strong among women and adults younger than 60. Those subgroup findings may help guide future research, but they do not necessarily mean muscle health is unimportant for men or older adults.
The UK Biobank also is not fully representative of the broader population. Its participants tend to be healthier and less socioeconomically disadvantaged than the United Kingdom as a whole, so the exact risk estimates may not apply to every group.
Even with those limitations, the study supports looking beyond body weight when assessing metabolic health. Two people with the same BMI can have very different proportions of fat and muscle, as well as different levels of strength, activity and diabetes risk.
“Health care professionals routinely monitor body weight and obesity, but our findings suggest assessing muscle health could help identify people at high risk earlier,” said Mario Siervo, the study’s senior project lead.
Future studies will need to determine whether adding measures such as grip strength or body composition meaningfully improves diabetes screening. Clinical trials would also be needed to establish whether interventions that preserve or increase muscle can reduce diagnoses among people with obesity.
Lead author Zhongyang Guan was supported by a Curtin University Higher Degree by Research scholarship. Blossom C.M. Stephan’s Chair in Dementia is funded by Dementia Australia. Stephan also reported serving as director of NeuroAnalyse.