The findings are published in the September issue of the Journal of Clinical Endocrinology and Metabolism.
"It's not just weight that matters, but what proportion of your weight is muscle mass," says study researcher Arun S. Karlamangla, PhD, MD, an associate professor of medicine in the division of geriatrics at the University of California, Los Angeles.
Researchers tapped into data from the National Health and Nutrition Examination Survey III on 13,644 adults who were not pregnant and had a body mass index (BMI) of at least 16.5. The researchers wanted to see how muscle mass affects insulin resistance, a precursor to diabetes.
For each 10% increase in the skeletal muscle index (ratio of muscle mass to total body weight), there is an 11% reduction in insulin resistance and a 12% reduction in prediabetes. Prediabetes is a condition in which a person's blood sugar is higher than normal, but not high enough to be diabetes. These relationships held even after the researchers took into account other factors affecting risk for insulin resistance and/or pre-diabetes.
"If you start an exercise program, and don't lose weight, you should not give up hope because your fat is getting converted to muscle," Karlamangla says. "If you lose fat, you gain muscle. So even if the weight is the same, the balance shifts."
"It's not too late if you already have type 2," Karlamangla says.
Muscle Mass and Insulin
John Buse, MD, PhD, chief of endocrinology at the University of North Carolina, Chapel Hill, says that muscle is one of the major insulin-sensitive tissues in the body.
"The more muscle mass you have, the more glucose you can dispose of in response to insulin," he says.
Insulin is a hormone that helps your body regulate blood sugar (glucose) levels. Left unchecked, high glucose levels can wreak havoc on the body and cause many diabetes-related complications.
Current exercise recommendations call for resistance training that involves all major muscle groups two or more day of the week, in addition to aerobic exercise.
When it comes to diabetes risk, "fitness trumps fatness," he says. "If you are a little heavy but fit you are probably well. If you are heavy and not fit, your risk of diabetes is higher," he says, adding that the ideal is to be both fit and trim.
Francesco Rubino, MD, chief of gastrointestinal metabolic surgery and director of the Diabetes Surgery Center at New York-Presbyterian in New York City, says that appropriate-for-your-size muscle mass can improve your metabolic efficiency and reduce risk of insulin resistance.
"The exercise that we always used to consider appropriate for reducing cardiovascular risk -- aerobic exercise -- may not be enough," he says. Resistance training may also be beneficial, he says.
Sedentary lifestyle is a known risk factor for diabetes, and it is believed that this is due to increased fat storage. There may be more to the story, Rubino says. "Sedentary lifestyle also decreases muscle mass."