Updated: Oct 10, 2021
TL;DR: Muscle does not turn into fat directly. Though, muscle loss can contribute to a faster rate of fat gain via indirect mechanisms.
Have you ever heard someone say "I used to be in good shape but all my muscle turned into fat"?
Everyone has seen the retired professional athlete who has become very obese, despite the fact that it does not seem to make any logical sense that muscle can become fat.
Muscle cannot simply convert into fat, there is no known mechanism that causes muscle tissue (primarily amino acids, protein, and water) to directly turn into adipose tissue (fat).
If muscle does not turn into fat, then what exactly is going on? In this article I'll explain why this seems to happen and how to prevent it.
Table of Contents:
Why Does Muscle Seem to Turn Into Fat?
Simply put, muscle tissue cannot be transformed into fat, and fat tissue cannot be transformed into muscle.
One exception to this is that the energy stored within fat tissue can be used to supply the required energy for muscle growth.
There are actually a few reasons why muscle seems like it turn into fat, such as the following.
Reduced total daily energy expenditure
Increased muscle protein breakdown
Increased rate of fat storage
A likely explanation for why people may believe their muscle has turn into fat is simple.
Muscle loss contributes to a faster rate of fat gain due to a reduced caloric requirement, meaning less calories are required by the body from the diet, this is why muscle seems to turn into fat, luckily there are ways to prevent this from happening.
This could be happening due to diet, training, lifestyle, or health issues, such as not training for a few months, drinking too much alcohol, illness, etc.
Amino acids within muscle cells can be broken down and released into the bloodstream during the catabolic process known as protein breakdown.
Some of the excess amino acids from protein breakdown can be used as an energy source within the body.
For example; if your total daily energy expenditure is 2000 calories while working out consistently 5 days a week, then you stop for a month and your body starts to break down some muscle tissue, your total daily energy expenditure will be less due to reduced exercise.
But not only due to reduced exercise, the muscle that is breaking down is releasing amino acids, these amino acids can be used for energy and may reduce the amount of calories you need to consume.
This extra energy essentially lowers the required daily caloric intake as more energy is being produced from broken down muscle tissue.
Due to this extra available energy, any fats and carbohydrates consumed in the body will increase the rate of fat storage.
This means that protein breakdown can contribute to the build up of fat tissue but muscle doesn't turn directly into fat.
If your weight stays the same, yet you look more bloated and like you have put on fat while your muscles look more deflated, this is a change in body composition.
This change in body composition causes the illusion of muscle turning into fat.
So, what exactly is going on here?
A change in body composition and an increase in body fat percentage is taking place. Essentially, the body is losing muscle mass and undergoing an increase in fat mass.
How to Prevent Muscle Loss
Muscle is constantly in a state of protein turnover, a fine balance between muscle protein breakdown and protein synthesis.
This balance is affected by a variety of factors, including the following.
As mentioned above, the more muscle you lose, the easier it will be to gain fat mass.
Below are the best ways to prevent muscle loss and muscle protein breakdown.
Exercising is the best way to prevent muscle loss and increase protein synthesis higher than protein breakdown, providing volume and intensity is high enough. (1)
Workout out using a combination of heavy weights, eccentric exercise and high volume can enhance muscle growth dramatically.
As you can see in the image above, myofibrillar and mixed muscle protein synthesis is increased after exercise in both trained and untrained individuals. (2)
An optimal hormone profile is essential for muscle growth and preventing muscle loss.
Testosterone is the major hormone in men responsible for muscle growth, maintaining optimal testosterone levels is crucial.
Without optimal testosterone levels, muscle protein synthesis is reduced and protein breakdown is elevated, testosterone has various other favourable effects on body composition too.
These hormones can help increase protein synthesis and reduce protein breakdown, the effects of growth hormone on muscle tissue seem to be largely IGF-1 dependant. (5)
Further Reading: Complete guide to IGF-1
The diet is essential for muscle growth and maintaining muscle mass.
Carbohydrates are critical in the right amount for muscle growth, protein is the most important dietary component for muscle growth.
A diet rich in vitamins, minerals and plant compounds are also excellent for improving muscle growth and overall health.
Daily protein intake has been found optimal between 1.6 and 2.2 g/kg of bodyweight. (6)
Protein has a major effect on muscle protein synthesis, increasing it dramatically.
Without adequate protein intake, the body is unable to sustain and create new muscle.
Further Reading: What is the best daily protein intake?
Creatine, ursolic acid, protein powder and other supplements have the ability to improve muscle growth via the following mechanisms.
Reduced muscle protein breakdown
Increased muscle protein synthesis
Improved hormone profile
Increased strength, endurance and recovery
Improved cellular signalling
There are other direct and indirect reasons why various supplements can enhance muscle growth and prevent muscle loss.
There are multiple supplements available to help improve muscle growth, some work better the others.
Further Reading: Read about various different supplements
Adequate sleep is also a very important factor in terms of muscle growth.
As mentioned earlier, sleep improves the level of GH and IGF-1, possibly increasing the ability of muscle growth.
There are other benefits associated with adequate sleep too.
Alcohol reduces protein synthesis dramatically, possibly even to the count of a 25% reduction. (7)
It also contains 9 calories per 1 gram of alcohol, meaning it is very calorie-dense and will increase the rate of fat storage.
Written by Billy White
Billy White is a qualified Kinesiologist and Personal Trainer. He is an aspiring bodybuilder, fitness enthusiast, and health and fitness researcher.
He has multiple years of experience within the fitness, bodybuilding and health space. He is committed to providing the highest-quality information.
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This evidence-based analysis of muscle converting into fat features 7 references, listed below.
1. Atherton PJ, Smith K. Muscle protein synthesis in response to nutrition and exercise. J Physiol. (2012, Mar) ✔
2. Jorn Trommelon. The Ultimate Guide to Muscle Protein Synthesis. (2021, Jul)
3. Takahashi Y, Kipnis DM, Daughaday WH. Growth hormone secretion during sleep. J Clin Invest. (1968, Sep) ✔
4. Chennaoui M, Arnal PJ, Drogou C, Sauvet F, Gomez-Merino D. Sleep extension increases IGF-I concentrations before and during sleep deprivation in healthy young men. Appl Physiol Nutr Metab. (2016, Sep) (Clinical Trial) ✔
5. Velloso CP. Regulation of muscle mass by growth hormone and IGF-I. Br J Pharmacol. (2008, Jun) ✔
6. Stokes T, Hector AJ, Morton RW, McGlory C, Phillips SM. Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training. Nutrients. (2018, Feb) ✔
7. Parr EB, Camera DM, Areta JL, Burke LM, Phillips SM, Hawley JA, Coffey VG. Alcohol ingestion impairs maximal post-exercise rates of myofibrillar protein synthesis following a single bout of concurrent training. PLoS One. (2014, Feb) ✔
✔ Citations with a tick indicate the information is from a trusted source.
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