Fatty deposits that run through a steak—known as marbling—improve the meat’s quality, making it more tender, juicy, and flavorful. However, evidence indicates that fatty deposits in human muscles may have adverse health effects. A recent study found that higher fat levels within muscles were associated with a 53% increase in the risk of major cardiovascular events, such as heart attacks or heart failure.

The study included 669 people undergoing routine cardiac evaluations. Researchers assessed their coronary flow reserve, which measures the capacity of the coronary arteries to increase blood flow during stress or exertion. They also measured body mass index (BMI—a proxy for body fatness), skeletal muscle mass, and fat levels beneath the skin and within the muscles. They monitored the participants for major cardiovascular events for about six years.

The researchers found that higher BMI, lower muscle mass, and more fat inside the muscles were linked to reduced blood flow in the coronary arteries, but fat under the skin was not. For every unit decrease in blood flow, the risk of a major cardiovascular event increased by 78%, and for every 10 cm² increase in fat inside the muscles, the risk increased by 53%. In contrast, larger muscles and more fat under the skin were associated with an 11% and 6% reduction in the risk of a major cardiovascular event, respectively.

These findings suggest that higher muscle fat content increases the risk of major cardiovascular events. Evidence suggests that exercise reduces muscle fat content, potentially explaining how exercise reduces cardiovascular risks. Learn more about how exercise protects the heart in this episode featuring Dr. Ben Levine.