Health: true or false?

Don't worry - stopping exercise won't turn muscle into fat

PUBLISHED : Monday, 06 July, 2015, 6:37am
UPDATED : Monday, 06 July, 2015, 6:37am

Do your muscles turn into fat if you stop exercising?

The straight answer: No

The facts: You might have been warned about this as a child: always stay active otherwise your muscles will turn into fat. But nothing could be further from the truth. The good news is, if you don't work out, your muscles will not transform into fat, simply because the two have completely different functions and are made up of completely different types of cells.

"Skeletal muscles are needed to maintain your posture, facilitate movement, and perform fine motor activities, such as writing and painting," says Joan Liew, co-founder and director of Fitness Factory in Singapore.

"Your muscles are made up of protein and are connected to your nervous system by neurons. Your stored fat or adipose tissue, on the other hand are made up of fat cells called adipocytes.

"The size of your fat cells increases when there is an accumulation of fat through an uptake of fatty acids into the adipocytes.

"So, fat and muscles are two exclusive components in the body and there is no way that one can turn into the other."

The phrase "use it or lose it" can definitely be applied to your muscles. When you stop working out, your muscles start to shrink, says Li Si-yang, a personal trainer from the US-based company Journey to Fitness.

"The real reason a person looks fat or flabby when he stops exercising is because he is not burning the number of calories he once did, and most likely he has not reduced his calorie intake, either. These extra calories that he doesn't burn off is what leads to his fat cells increasing in size, and also, excess fat storage.

"But when he starts working out again, a different process occurs - his muscles increase in size and his fat cells shrink, causing him to look lean again."

Due to our body weight, prolonged periods of sitting or lying down can actually subject our body tissues to "mechanical stretching loads", which cause preadipocyte cells - the precursors to fat cells - to turn into fat cells faster and produce even more fat, according to a study by Tel Aviv University researchers.

Their study, published in 2011 in the American Journal of Physiology - Cell Physiology, demonstrates another damaging effect of a modern, sedentary lifestyle. Researcher Professor Amit Gefen noted: "Obesity is more than just an imbalance of calories. Cells themselves are also responsive to their mechanical environment. Fat cells produce more triglycerides, and at a faster rate, when exposed to static stretching."

Bottom line: keep active. If you don't reduce your calorie intake in relation to the decrease in your physical exercise, you will gain body fat as a result of the excessive intake of calories, and not because your muscles have morphed into fatty tissue.