The claim that muscle turns into fat when you stop working out is false, according to Prof Leigh Breen, a specialist in muscle physiology at the University of Leicester. He says the statement is one he hears often, particularly from people who have taken a long break from exercise, who refer to their muscles having "softened" or no longer feeling as toned.
No Biochemical Link
Muscle and fat are distinct types of tissue, and there is no process in the human body that would support one turning into the other, Breen explains. The confusion, he suggests, comes from what happens when someone stops exercising, especially resistance training.
People may begin to lose some of the muscle they built through training. If they continue eating the same amount while exercising less, they may end up with an energy surplus, which can lead to an increase in body fat.
Why the Confusion Persists
"This combination of a reduction in muscle mass and potentially an increase in fat mass can give the impression that one is turning into the other," Breen says. "Which isn't the case."
Taking a couple of weeks off a usual training routine while remaining relatively active is likely to result in fewer changes than being completely immobilised for an extended period due to injury.
Managing Muscle and Fat During Breaks
Diet during an exercise break can influence how much muscle and fat mass is gained or lost. Breen recommends keeping protein intake high while slightly reducing calorie intake.
He notes that bodies are constantly changing, and small fluctuations in muscle and fat mass during training breaks are generally normal. "Slight fluctuations are generally nothing to worry about, as long as over the course of months and years consistent exercise and dietary habits have been maintained," he says.
