Low Carb Intermittent Fasting and Building Muscle

Fasting and Building Muscle

The Short Answer: Can You Build Muscle while Fasting?
Studies would indicate that fasting is not a detriment to building muscle and may in fact help retain more muscle tissue than normal when dieting.

Intermittent Fasting especially when combined with a Low Carb Diet is a great way to lose weight, you can read more about it all the reasons why here. But what about fasting and building muscle, or retaining that hard earned muscle you have built up after years of training?

Most of us familiar with strength and conditioning training understand how important nutrition is to the process of building muscle. So, with that in mind it’s only natural to ask:

  • Do the long fasting periods when no calories are consumed impact muscle gain and retention?
  • Does Low Carb Intermittent Fasting ( LCIF) lead to a loss of muscle tissue? (Catabolism)
  • Does it make no difference to building muscle whatsoever? Or does the body adjust and hold on to muscle more efficiently due to LCIF?
  • Does the Low Carb aspect of LCIF play a role?

In the following article I’m going to cover what impact LCIF has on building muscle and retaining muscle and explain why the answer depends on a number of factors.

What the Science Says

The science for the most part is not completely settled when it comes to whether there are any advantages to building muscle thanks to fasting. Clinical studies have shown some potential but it’s fair to say there are too many variables to take into consideration e.g. the type of intermittent fasting you are undertaking. Your training program and intensity, Protein intake, and whether you are in caloric surplus to name just a few.

Caloric Surplus and Muscle Gain
While most people consider LCIF a tool for weight loss, the truth is you must also be in a caloric deficit. LCIF may potentially help exacerbate weight loss when in caloric deficit but strictly speaking consuming less calories than your body needs to maintain its current weight is key.

To add weight we must be consuming more calories than our body requires to maintain current weight e.g. Caloric surplus. But eating in a caloric surplus is only half the battle. For muscle growth to occur rather than storing excess body fat as a result of the extra calories we need to stimulate muscle growth and consume enough Protein for the body to build new tissue.

On the other hand, there is little to suggest fasting hinders muscle growth compared to a standard diet in any capacity. This is great news for those concerned fasting would have an impact on their ability to build muscle.

Retaining Muscle

Strength Training

Intermittent fasting has demonstrated in clinical trials an ability to help retain muscle. Here’s just a few of the studies showing favourable outcomes.

What’s truly exciting about these results is the fact that Intermittent fasting may help the body prevent muscle loss more effectively while dieting.

From a weight loss perspective the more lean mass your body holds the faster your metabolism, as muscle tissue is the most metabolically active tissue in the body. In fact you could say retaining muscle is an important component of weight loss.

Intermittent Fasting may also combat Sarcopenia (muscle loss due to ageing) normally as a result of a natural decline in Testosterone as we age.

Where does Low Carb Fit into This?

It’s also true that clinical studies have demonstrated the benefits of a Low Carb Diet when it comes to muscle retention:

However, you should also consider the fact that when you lower your Carbohydrate intake you are more likely to increase your Protein intake which plays an important role in  building muscle.

How much Protein do I need to keep or grow muscle?

In most cases a good starting point is between .85 and 1 gram of protein per pound of body mass, if you are serious about preserving lean mass. Recent studies have shown that less Protein than this may be needed however so it’s best to track your progress. You can then make adjustments based on how your body is responding.

*It’s important to note that for some this amount of protein may be unhealthy. For those with liver disease for instance, we recommend you consult your doctor before making dramatic changes to your diet.

Evidence for Increased Muscle Retention

I have seen the benefits of Low Carb Intermittent Fasting when it comes to muscle retention first hand.

In late 2018 I developed Bursitis in my right shoulder along with some joint wear and tear and a partial thickness tear of the Subscapularis Tendon. Nothing too serious long term but enough to keep me out of the gym for longer than I had hoped.

I’m a proponent of full body training and as a result most of my workouts could be considered fairly shoulder-centric. E.g. it’s difficult to bench press, overhead press, deadlift or even squat (due to maintaining bar position) with a shoulder injury.

The injury took some time to heal e.g. up to 6 months to get back to training at anywhere near full strength and I’m a bit of a geek when it comes to nutrition and strength training. As a result I have maintained a spreadsheet to track my performance and body composition for the past 3-4 years. And despite not training for many months found that I had been able to retain almost all of the muscle I have added to my frame in this time despite being in my forties when muscle retention becomes even more challenging and being far more sedentary than normal while the injury healed.


While it’s not possible to provide a definite answer on whether Low Carb Intermittent Fasting provides any real benefits for building muscle, it is highly likely that it does assist with muscle retention.

But, it’s really not that simple.

To build or preserve muscle the standard protocols must be observed e.g. you must be in a caloric surplus, or at least not in a caloric deficit to retain muscle. You must be stimulating muscle growth through strength training at a high enough intensity and you must be consuming enough Protein to build muscle tissue. Without these three conditions in place fasting and building muscle will prove to be difficult.

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