Intermittent fasting and muscle gain: SIMPLE’s five tips for muscle gain while fasting

Written by Trey Reck

Medically reviewed by Josie Porter, RD

Published on February 23, 2023 | Updated on March 28, 2024

If you’re looking for a way to get swole, intermittent fasting may not be your first choice. 

It’s not necessarily the most obvious nutrition method for building muscle mass. But it can be an effective one if you use it right. Curious?

Let’s dive into the ins-n-outs of intermittent fasting and muscle gain. 

Is it possible to gain muscle while intermittent fasting?

There’s not a huge amount of research on muscle-related outcomes of intermittent fasting [1], probably because intermittent fasting is most often done to lose fat, not gain muscle. But there are things we know about how to eat and train to build muscle that are entirely compatible with an intermittent fasting lifestyle. 

Like how to put on muscle mass, you’ve gotta:

• eat more calories than you burn (ideally)
• have enough protein to build new muscle tissue [2]
• do sufficient exercise stimulus to cause growth [3]

Can you do all that to build muscle while fasting? Yes. 

You will have to work hard to get the results you want, mind you. 

You’ll need to pay attention to the timing of your meals and the kind of foods you’re eating. You’ll also need to think carefully about the type of exercise you do and how and when you do it.  

But you’d have to pay attention to these things anyway. Bulking up isn’t an easy ride. You can’t just randomly do any old thing, and boom, bigger biceps! Your processes have gotta be dialed in.

So, what can help you maintain muscle during intermittent fasting?

No surprise here that resistance training — training with weights to increase muscle strength, power, and/or size — is top of the list. Resistance training is your staple go-to for muscle preservation when trying to lose weight through any kind of dietary restriction.[4] 

Using your muscles regularly in ways that challenge them is one of the things you can do to make sure they stick around (“use it or lose it” is a real thing). 

This is just as true when intermittent fasting.[5] Here, a group of men retained all their muscle following a 16:8 intermittent fasting plan while also losing body fat.[6]

Cardio can prove pretty valuable, too. This study on alternate day fasting showed that 25–40 minutes of bike or elliptical, done three times each week, also helped to maintain lean mass during weight loss.[7]  

Some trainers say cardio interferes with muscle gain. It can if you do too much or a lot of high-intensity stuff. 

But, 2–3 sessions of moderate-intensity cardio can be super helpful because it builds your aerobic fitness. That’s going to come in pretty handy when it comes to lifting heavier weights. Even a set of three can get you breathing hard! 

So whether you like to drop it like it’s squat or you’re a cardio enthusiast, exercise is a big part of keeping your muscle where it belongs—on your body. 

How to gain muscle while intermittent fasting

If you want some boulder shoulders or some extra junk in your trunk, you’re gonna need to dovetail your intermittent fasting with a muscle-gain diet. 

Here are some key factors to consider. 

Eat more than you burn (ideally)

To lose fat, you eat less than you burn so that your body uses your fat stores for fuel. 

To grow muscle, you’d usually eat more than you burn so that your body has raw material to make new muscle tissue from. You gotta give a body something to work with! 

(That said, it actually is possible to build muscle in a caloric deficit,[8] assuming protein intake is sufficient. This may not be the most efficient way, but it can be done!)

Often, we just automatically associate intermittent fasting with eating fewer calories, but calorie restriction isn’t mandatory. You can eat as much as you need so long as you can fit it all in during your eating window. 

Choosing the right intermittent fasting protocol will be important here. If you haven’t got yours locked in yet, try our SIMPLE quiz, and we’ll get you set up with an intermittent fasting plan that’ll work for you. 

Eat sufficient protein and carbs

A decent chunk of your daily food intake needs to come from protein. 

Protein is what your muscles are made of, so eating enough of it means your body has what it needs to make more.[9] And it works best if you distribute your protein intake throughout the day (rather than, say, saving it up for your evening meal).[10] 

Aim to get at least a portion of protein with every meal, and shoot for around 0.6–0.9 g per lb. of body weight every day to support muscle growth.

Carbs matter for muscle too.[11] If you want to get after those heavy weight sessions, your glycogen stores need to be well stocked. (Plus, insulin is anabolic!) 

Aim for 1.8–3.2 g of carbs per lb. of body weight daily.[12]

If you need more ideas on what to eat to keep your protein-n-carb game strong during intermittent fasting, we gotcha covered.

Eat before and after you work out 

For optimal results with muscle gain while intermittent fasting, think about the timing of your meals relative to your workouts. 

Ideally, hit your training session when you’re well-fed. To lift heavy — the essential workout practice of any budding muscle boy, girl, or enby — you need some available energy in the tank. 

Then eat afterward to jumpstart the muscle repair and recovery process. (And to top your energy levels back up). 

Ideally, get this meal in within two hours of finishing your workout, but don’t worry too much if you can’t. Focus more on getting enough quality food during your eating window overall. Your body will be able to do its thing with the nutrition you give it, even if your post-workout timing isn’t “perfect.” (It’s clever that way.)

Do I have to train fasted to gain muscle while intermittent fasting? 

Some people say that training fasted—i.e., working out on an empty stomach or before you break your fast—helps you gain muscle while intermittent fasting. 

The idea is that training this way may release more human growth hormone (HGH), one of the hormones intermittent fasting is thought to increase. So by combining intermittent fasting and fasted training, you potentially get a double hit of HGH that makes your attempts at building muscle even more effective. 

But our science team is skeptical. The evidence on this is scarce at best. 

Most of the evidence we’ve seen says that training fasted has a very similar effect to training fed.[13] And most studies of intermittent fasting and weight training have not used fasted exercise.

Even if it were true, the real decider on whether you should train fasted or not is—your body. 

Some people get on great with it. They turn into spry, lithe cheetahs as soon as their feet hit their sneakers. Other people find it makes them feel like a lunch-obsessed walrus dragging its empty-bellied butt through thick, gloopy mud.

So here’s the question. Will training fasted improve your workout performance? 

If it will, go for it. Drink plenty of water during and be sure to get some protein in afterward (ideally 20+ g).[14]

If not, skip it. 

Which intermittent fasting plans promote muscle gain the most?

16:8 is often said to be the best intermittent fasting plan for muscle gain. 

Why is that? Well, let’s see. 

1. The eating window is 8 hours 

Plenty of time to get in the calories and protein you need. Whereas something like the Warrior Diet, with its 4-hour eating window, might be more of a challenge. 

2. It’s a daily intermittent fasting plan

Compared to plans like the 5:2 diet or alternate day fasting, where you have 2–4 days per week on just 500/600 calories, you can eat well every day on 16:8. 

That’s going to help with consistency in your eating habits, as well as making sure you get all the energy you need for muscle growth. 

3. It’s pretty easy to stick to 

16:8 is popular as it makes for an easier fast (most of it’s overnight), and the eating window sits snugly inside a regular day (albeit one with a late-ish breakfast or an early-ish dinner). 

Bottom line:

Whichever intermittent fasting plan you find easiest to stick with is the one that’ll work best for any goal, muscle gain included. So while 16:8 has some solid credentials (and we think 14:10 and 12:12 would also be a good bet), feel free to explore what works best for you. 

And if you’re looking for a little more help deciding what your best approach is, we gotcha! Try our SIMPLE quiz, and we’ll help you get started on your intermittent fasting journey today.

Intermittent fasting and exercise

We talked about resistance training to preserve muscle earlier.[15] For building muscle, resistance training remains the star of the show.[16]

So when you’re planning how you’ll approach intermittent fasting and working out, here’s what you need to know:

Exercise that builds muscle on intermittent fasting is the same as exercise that builds muscle full stop. 

You can train like a bodybuilder and split your workouts into muscle groups: 

• Monday—chest and triceps
• Wednesday—back and biceps
• Friday—legs
• Saturday—shoulders and abs

Or you could train with a movement pattern focus:

• Monday: Upper body, Push pattern
• Tuesday: Lower body, Squat pattern
• Thursday: Upper body, Pull pattern
• Friday: Lower body, Hinge pattern

Or, you could keep it full body and do supersets (s/s) every session:

• Monday: Back squat s/s push-up, lunge s/s shoulder press
• Wednesday: Deadlift s/s hip thrust, incline bench press s/s RDL
• Friday: Pull-up s/s goblet squat, split squat s/s overhead press 

You can use low reps and heavy weights, moderate reps and moderate weights, or lighter weights and higher reps. Ideally, do all three (they all play a different but valuable role). 

The point here is this: 

There are lots of ways to build muscle. 

You do need to address certain aspects for muscle building. Things like muscular tension, progressive overload, correct timing on rest breaks, etc. As it goes beyond the scope of this article to get any deeper into the weeds on this one, here’s our suggestion for the next step:

• Seek out a program from a skilled trainer you like and trust 
• Try it for three months minimum. 
• Test for enjoyment* AND results.  

*Just like with intermittent fasting, the plan you can stick to long term is the one that’ll work best for any goal you have. Enjoyment is key. 

Can you lose muscle mass while intermittent fasting?

Sure you can. 

If you eat less than you burn while intermittent fasting, you’ll lose weight. The kind of weight you lose could be muscle. (More about this here: fat loss vs. weight loss.) 

Whether you lose muscle or fat will depend on how much (and how fast) you cut your calories, whether you train with weights or not, how much stress you’re under, and so on.  

So it comes as little surprise that some studies show that intermittent fasting can lead to muscle loss [17] while other studies show the opposite.[18,19] There are many variables at play. 

It’s encouraging, though, that some research suggests that intermittent fasting may be more effective than regular diets at preserving muscle mass.[20]

Here’s the bottom line on this: you can lose muscle while intermittent fasting, but you can also preserve and build muscle.

It all depends on how you approach it. 

Five tips on how to gain muscle while intermittent fasting

We’ve covered the headlines: Eat plenty, get your protein in, lift some weights, etc. 

Here are a few other ideas that’ll help. 

1. Get clear on your goal

Why do intermittent fasting and building muscle matter to you? 

Whether you want to get ripped, compete in powerlifting, or Turkish Get Up a 100 lb. kettlebell, know your goal. If you don’t know where you’re headed, it’s easy to go around in circles. 

2. If you’re just getting started, take it easy 

Building muscle is a progressive thing. It takes time to learn good technique, work up to heavier weights, and master the more complex movements. 

Be patient. Don’t allow your ego to push you to run before you can walk. It’s just a super quick route to getting hurt. (Yup, we’ve been there!)

3. One thing at a time

There’s a lot of depth to these processes of intermittent fasting and gaining muscle. Get good at one before moving on to the next. 

For instance: 

• Start fasting. Practice doing that for a week or so. 
• Then look at increasing your protein intake. Practice that till you get it down. 
• Next, try improving the quality of your carbs or increasing your veggies. Run with that till it feels smooth. 
• Spend the next week focusing on getting your meal timing to jive nicely with your workout schedule. 

These are just ideas. It doesn’t matter what order you do the things, so long as you take it one step at a time. 

They’ve got more chance of sticking that way. 

4. Invest in your mobility 

To win the game you gotta be in the game … and the fastest way to be out of the game is to get injured. 

A short mobility session a few times a week will help your joints stay supple, strong, and capable of getting into the loaded positions that you’re asking of them in your strength workouts. 

5. Get enough sleep

When it comes to building muscle, recovery is essential. And when it comes to recovery, sleep is king. 

When you’re training hard, you gotta be sleeping hard, so you can keep pushing yourself every session.

Quality sleep is also going to help keep your hunger and cravings in check, so you can keep making smart food choices that support your muscle growth.

If you’re getting less than 7–9 hours a night and that’s not feeling great for you, try and stretch your sleep time out over the coming weeks. Adding 15 minutes a week can be an easy win that brings meaningful benefits over time. 

Oh, and if you can, don’t train too close to bedtime.[21] You need both sleep AND training, but ideally, you don’t want them having to duke it out. 

Written by Trey Reck

Medically reviewed by Josie Porter, RD

Published on | Updated on March 28, 2024