Does Muscle Turn to Fat when You Stop Exercising?

The issue of whether or not muscle turns into fat when you stop exercising causes more than its fair share of confusion. I don't know how this confusion came about, but my guess is it had something to do with people making assumptions based on personal experiences. Interestingly, the science behind this issue is fairly basic and straightforward, so things should be cleared up by the end of this article.

The simple answer is that muscle does not turn into fat when you stop exercising. Everyone has muscle cells and fat cells, but they are completely different types of cells and it is impossible for one type of cell to turn into the other one. In other words, muscle cells can never turn into fat cells and fat cells cannot change into muscle cells. It is just not physically possible. However, there is a reason why it may appear that muscle turns to fat when you stop exercising.

However, before getting to that, here is little basic physiology to help understand this issue. For the most part, the number of muscle cells in your body does not vary, although in cases of extreme high volume resistance training, it is possible to create some new muscle cells. For all practical purposes, the quantity of muscle cells does not change, although the properties of each cell can change significantly.

Exercise, especially with challenging weights and high numbers of sets and reps, creates a stimulus for muscles to grow, causing the individual cells become larger. As long as you continue to challenge your muscles, they should maintain their larger size or possibly continue to grow, depending on the workouts. Of course, as you age, physiological changes occur, such as decreasing hormone levels, which eventually cause your muscles to slowly shrink, regardless of your exercise routine.

While aging results in decreases in muscle size and function, it is nothing compared to what happens when you stop exercising. When your muscles are no longer exposed to an exercise stimulus, the individual muscle cells start returning to the size they were before you started exercising. The longer you go without the stimulus, in this case lifting weights, the smaller your muscle cells become. The important thing to note is these muscle changes occur regardless of what your fat cells are doing.

Fat cells may be making changes of their own during this time, but those changes are due to reasons not directly related to a lack of exercise. Most notably, when people stop exercising, they often do not change their eating habits or they may eat more. If your calorie intake increases or even stays the same when you stop exercising, then you will most likely gain weight and fat.

When you stop exercising, your body will not burn as many calories and your metabolism can slow down, so you need to adjust your caloric intake to reflect those changes. If you eat the same way you did while you were exercising, you will consume more calories than you burn, causing your fat cells to increase in size. Plus, unlike muscle cells, fat cell can increase in number when calorie intake is too high, which makes fat gain even more likely.

In these situations, it may appear as though your muscle is turning into fat, but it is actually two completely different physiological changes taking place simultaneously. If you stop exercising and make an appropriate reduction in your caloric intake, to reflect your new lower level of daily calorie burning, then you will not gain much if any fat.

However, you will still lose your prior fitness improvements and muscle gains, which eventually results in a further decrease in metabolism and may cause fat gain in the future. That said, exercising should be a life long habit and hopefully you won't go through a long period of time without exercising, in which case this will not be much of an issue.

To sum up, muscle does not turn into fat when you stop exercising and you can lose muscle without gaining a significant amount of fat. Changes in muscle and changes in fat are certainly related, but they are still different physiological processes that are each affected separately by your exercise, nutrition, and lifestyle choices.

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14 years of experience and education in health and fitness