Hidden fat, also known as intermuscular adipose tissue, describes deposits of fat that build up directly between muscle groups or between individual muscle fibers.
It is considered as a form of ectopic fat, which refers to the accumulation of fat in nonadipose tissues, such as the muscles.
Previous research has highlighted that the infiltration of fat within muscle can have a negative impact on health, and may be associated with aging, metabolic conditions, such as type 2 diabetes, and cardiovascular events, such as heart attacks. Conversely, evidence indicates that lean muscle mass is associated with better health outcomes.
However, as the name suggests, unlike visible body fat, hidden fat is not easily detectable and can be difficult to measure accurately and reliably. Now, a new study utilizing advanced artificial intelligence (AI) to analyze muscle composition from MRI scans may be able to better identify hidden fat.
Adding to growing research, the imaging study, published in the Radiological Society of North America’s journal Radiology, suggests that fat hidden deep within muscles could be an underrecognized risk factor for cardiovascular and metabolic health problems, even in those who appear otherwise healthy.
The study included more than 11,000 adults with no known pre-existing conditions. Participants underwent whole-body MRI scans, which were analyzed using a deep learning algorithm to measure both lean muscle mass and intermuscular fat in muscles along the spine.
The researchers identified a clear pattern that higher levels of intermuscular fat and lower muscle mass were associated with worse cardiometabolic health.
Despite being considered healthy, many participants showed previously undiagnosed risk factors, with 16.2% having high blood pressure, 8.5% with unstable blood sugar levels, and 45.9% with unhealthy lipid profiles.
After accounting for various factors, such as age, sex, and physical activity, higher levels of hidden muscle fat were still linked to a higher risk of hypertension, difficulty managing blood sugar, and unhealthy cholesterol levels.
Notably, a greater lean muscle mass appeared to protect against these risks, but only in males.
For females, muscle mass remained relatively stable until midlife, then declined significantly between ages 40 and 50. While still unclear, hormonal changes during menopause may explain why these protective effects were not observed in females.
Cheng-Han Chen, MD, board certified interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA, spoke to Medical News Today and suggested a potential role of estrogen:
“It is not clear why lean muscle mass was associated with lower prevalence of cardiovascular risk factors only in men and not in women. These results may be confounded by the sex-specific effects of estrogen on both muscle mass and those same risk factors.”
The study findings reinforce the role of lifestyle factors, highlighting that lower physical activity levels were associated with higher hidden fat and lower lean muscle mass.
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As such, this suggests that regular movement and strength-building exercise could help reduce hidden fat and improve muscle quality.
This aligns with previous research noting that aerobic and resistance exercises are effective for preventing muscle fat infiltration and improving muscle mass, particularly in older adults and those living with chronic conditions.
Current guidance from the American Heart Association (AHA) recommends that adults aim for at least 150 minutes per week of moderate-intensity aerobic activity, such as walking, or 75 minutes per week of vigorous aerobic activity, such as running, or a combination of both spread throughout the week.
It is also advisable to add moderate to high intensity muscle strengthening activities, such as resistance or weights, on at least 2 days per week.
“This study found an association between intramuscular fat and increased prevalence of cardiovascular risk factors such as high blood pressure and high cholesterol,” Chen noted.
“These results reiterate the importance of proper muscle composition and mass on maintaining good health, and support recommendations to incorporate regular strength training into a heart-healthy exercise regimen,” he added.
“These results reiterate the importance of proper muscle composition and mass on maintaining good health, and support recommendations to incorporate regular strength training into a heart-healthy exercise regimen.”
– Cheng-Han Chen, MD
The findings point to a potential new way to identify people at risk of cardiometabolic disease before symptoms appear, by using muscle composition as a reliable imaging biomarker.
Notably, it could also help identify people who seem metabolically healthy by traditional measures, but may actually be at higher risk.
As MRI scans are already widely used in clinical practice, the researchers suggest they could be repurposed to assess muscle composition without additional procedures, providing a more detailed picture of a patient’s health.
While the results are promising, additional evidence is needed to define the role of muscle composition in disease risk.
“Further research will be necessary to determine how we can best use muscle composition as a tool to identify people at risk of cardiometabolic disease,” Chen concluded.
