The health consequences of excess visceral fat tissue are well known. But there is another type of fat accumulation in the body that increases the risk for type 2 diabetes and cardiovascular diseases. In Molecular Aspects of Medicine, researchers warned that the dangers arising from intramuscular fat tissue are often underestimated.
“Everyone knows the dangers of abdominal fat or that the deposition of fat in the coronary arteries can cause a heart attack,” said lead author Osvaldo Contreras, PhD, from the School of Clinical Medicine at the University of New South Wales in Sydney, Australia. “But hardly anyone has ever heard of fat accumulation in skeletal muscles, even though they are associated with a whole range of life-threatening diseases.”
“The work emphasizes that muscles are not only good for standing, walking, or lifting a box. They are metabolically active, produce hormones, communicate in the body, and can positively or negatively affect a person’s health,” Yurdagül Zopf, MD, PhD, professor of integrative medicine specializing in nutritional medicine and director of the Hector Center for Nutrition, Exercise, and Sports at the University Hospital Erlangen, Erlangen, Germany, said in an interview.
Associated With Diseases
Increased intramuscular fat is found in various conditions where muscle mass is increasingly lost and replaced by fat and connective tissue. Intramuscular fat has been observed, for example, in patients with chronic muscle diseases, sarcopenia, hormonal disorders, and metabolic diseases such as insulin resistance and type 2 diabetes, as well as in patients with cardiovascular problems such as hypertension and heart failure.
Fat accumulation in the muscles, like all fat deposits in the body, can result from an unhealthy lifestyle with excessive calorie intake and, especially, lack of exercise. “If the body has more energy available than it can use, it will initially store it as subcutaneous fat,” said Dr. Zopf. “Once these storage capacities are depleted, more and more visceral fat is deposited, and then more and more fat is stored in the organs and the muscles.”
Movement plays a particularly important role in intramuscular fat. “We know that the less physically active someone is, the higher the risk that fat will be stored in the muscles,” said Dr. Zopf.
Arising From Injuries
Unlike other fat tissues in the body, intramuscular fat can also accumulate in higher amounts when there are injuries to the muscles. The group led by Dr. Contreras and lead author Marcelo Flores-Opazo from the Universidad de O’Higgins in Rancagua, Chile, emphasized the role of fibroadipogenic progenitor (FAP) cells in their review. “FAPs play a crucial role in preserving and repairing muscle tissue injuries. They can differentiate into fibroblasts and adipocytes and are responsible for depositing fat and connective tissue in response to muscle injuries.”
Studies suggest that exercise can prevent FAPs from differentiating into fat and connective tissue cells. Metformin can achieve a similar effect in vitro. Dr. Contreras and colleagues hope that drug-based ways to reduce muscle fat will emerge in the future.
But how do you determine whether a patient has too much intramuscular fat? Although MRI and CT can be used for quantification, these are not routine examinations. There is currently no simple way to determine the fat content in muscles, according to the authors. The study authors hope that advances in molecular testing, imaging, and biopsies will improve diagnostic capabilities in the future.