Meal times and fasting

Does intermittent fasting lose muscle mass?

5 min read

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25 Jul 2023


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  1. What is intermittent fasting?
  2. Does intermittent fasting help you lose weight?
  3. Does intermittent fasting lead to muscle loss?
  4. When should you be in a cutting/fasting phase?
  5. How can Crazy Bulk help you gain lean mass?

Intermittent fasting is one of the biggest diet trends of the past few decades. For many people, it really works, thanks to it being straightforward to follow. Some use this technique on their own, but it can also be used as part of a bulking and cutting cycle. 

If you are using fasting as part of a bulking and cutting cycle, you will inevitably be worried about muscle loss. 

We all know that starving ourselves puts us at risk of muscle loss… but how long do we have to fast before the muscle loss begins? 

Is there a method of fasting that allows us to maintain lean muscle mass? 

Let’s take a look at whether intermittent fasting really causes muscle loss.

What is intermittent fasting?

Intermittent fasting is a dieting method that has many variations. The key element that links all of the diet plans, is that they involve fasting (i.e. eating nothing or close to nothing) for a short period of time. You then eat normally for a while and go back to fasting intermittently.

Intermittent Fasting Methods

One of the most popular plans is the 5:2 diet - eat ‘normally’ for five days and significantly restrict calories for the other two days of the week. Ideally, the dieter would eat the same number of calories that they burn on five of the days, and eat 25% of the calories they burn on the two fasting days. 

Stopwatch timer

So someone who burns 2,500 calories per day would eat 625 calories on their two fasting days, meaning they would burn 3,750 calories more than they eat every week. To lose one pound of fat, you have to burn 3,500 calories, so you would expect to burn a pound per week on this diet. 

This is a sustainable rate of weight loss, meaning that keeping the weight off after your diet is very achievable. The diet is really easy to follow as you only have to deal with hunger pangs and craving two days per week. Many find this much more manageable than a daily calorie deficit. 

Other intermittent fasting diets include the one meal per day method, alternate day fasting and time-restricted eating where you can only eat between certain hours of the day i.e., you can eat what you like for 8-12 hours per day and fast the other 12-16 hours.

Does intermittent fasting help you lose weight?

Any diet that creates a consistent calorie deficit over a number of weeks or months will lead to weight loss. So yes, intermittent fasting can absolutely lead to weight loss. 

Often people fall down because they overeat when they aren’t fasting. This can mean their overall calorie intake is higher than they realize because they aren’t counting their calories on those days. This might still lead to weight loss, but progress will be slower. 

Intermittent fasting weight loss

However, the real question is, are you losing solely fat? 

Or do intermittent fasters risk losing their hard-fought gains?

Does intermittent fasting lead to muscle loss?

Because intermittent fasting is primarily a weight loss tool rather than a bodybuilding diet, there isn’t as much research into this as we might like. It is generally thought that a fast that lasts less than 24 hours won’t cause a significant decrease in muscle mass.

Studies have shown that you can prevent muscle loss while fasting by engaging in resistance training. So if you are tempted to work out less when fasting because of low energy levels, don’t! Get yourself back to the barbell and cling to those gains!

Muscular man

It also really matters what you eat during a fasting diet. If you are on the 5:2 diet, those 500-700 calories you do eat on your fasting days should come from high-quality food with plenty of protein. 

What about an extended fasting period?

If you want to maintain existing muscle mass and build more lean body mass, then we don’t recommend extended fasting. After a day or two without proper nutrition, your body will start to break down muscle mass to use as energy. You will also start to find any cardio or resistance training really tough. You need proper fuel for your workouts to make the most of them.

When should you be in a cutting/fasting phase?

If your overall goal is to lose weight and increase lean mass, then a cutting and bulking cycle is a tried and tested method to improve your physique. 

A bulking phase usually lasts longer than a cutting phase i.e. 3-4 months vs 2-3 months, but that does depend on an individual's tolerance for the inevitable fat gain during the bulking phase.

You don’t have to fast during a cutting phase, you can simply eat a little less than you burn every day, but many find they get better results with the intermittent fasting method.

How to know if you should be cutting/fasting:

  • You have been gaining muscle for a number of months but have gained significant fat alongside that muscle
  • Your body fat is higher than 15% if you are a man and 25% if you are a woman
  • You want to look leaner 

Related content: Bulking vs cutting: what is the difference?

How can Crazy Bulk help you gain lean mass?

The world is full of diet methods, fasting, keto, paleo, and Mediterranean, but they all have two things in common. They can be really tough to stick to, and it can take a long time to get the results you want.

If only there was a way to make cutting a little easier and get better results.

Enter CrazyBulk

CrazyBulk bodybuilding supplements are a natural, safe and legal alternative to steroids. We have a range of products and stacks to work with you at every stage of your bodybuilding cycle. 

If you are embarking on a cutting phase using the intermittent fasting method, then check out our Cutting Stack. It helps you lose body fat, and it boosts your testosterone, energy and power to ensure you maintain performance at the gym and hold onto all the muscle you’ve gained during your bulking phase.

Maintaining muscle during intermittent fasting

Intermittent fasting doesn't have to lead to the loss of muscle tissue. You can do a few simple things to ensure that you maintain your muscle mass while reducing your body weight.

  • Prevent muscle protein breakdown by ensuring you keep your dietary protein intake high so that your body has all the essential amino acids it requires to maintain its lean mass.
  • Ensure you keep your weight loss to 2 pounds per week or less so that your body doesn't start to burn muscle for energy usage.
  • Stay consistent with your resistance training, you may even manage to gain muscle during your cut!
  • Avoid extended periods of fasting i.e., more than 24 hours, as this could lead to muscle loss.
  • Use an effective, safe workout supplement like CrazyBulk to improve your metabolic health, maintain lean body mass and speed up muscle growth

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