Can you build muscle while intermittently fasting?

In a world full of quick fixes and weight-loss fads, intermittent fasting is showing some staying power. Even those in the strength training world are getting a bit curious, so we want to know: is intermittent fasting good for building muscle?

Most studies on intermittent fasting have looked into its effect on weight loss, where it can be an effective tool for getting past a plateau. Limited research into intermittent fasting paired with regular resistance training suggests that while someone who is intermittent fasting may lose more weight than someone on a regular diet, their muscle gains and maintenance will be largely identical.

According to Advanced Sports Dietitian Lisa Middleton, committing to intermittent fasting or any restrictive diet mostly comes down to whether it can work for you. So, can you build muscle while fasting? Potentially. But before trying it, here are four things you should know.

1. You still need to train at full capacity

If your goal is to build muscle, sticking with intermittent fasting can be tricky. Muscle growth requires an excess of calories and a good amount of healthy protein.

First problem: cramming enough calories into a restricted window can make you feel like you’re constantly eating, which is not as fun as it may sound. Second problem: if you’re not getting enough calories, your workout performance can slip – meaning you’ll be less effective at building muscle and strength.

“Unless you’re primarily working out to lose fat, you should at least have a snack of protein and carbs 1-2 hours before you exercise,” Lisa says. “Plus, trying to fit all your daily protein into one or two meals isn’t as effective as spacing it out over a longer period. Ideally, eat food containing at least 25-30 grams of high-quality protein once every few hours to fuel muscle growth.”

“The key is finding the calorie intake that supports your fitness goals and eating in a way that suits your lifestyle,” Lisa says. “If you train best first thing in the morning, but you don’t eat your first meal until noon, you won’t be feeding yourself for optimal recovery. You could even lose muscle mass.”

4. You can still gain fat

Intermittent fasting – specifically fasting for muscle gain – will only be effective if you’re still eating the right foods. If you cram that window full of high-cal, high-fat, high-sugar junk food, you will bulk up... but with fat, not lean muscle mass.

“Not all calories are created equal,” Lisa says. “For muscle gain, quality of protein is key, and many overly processed foods lack the right type. Your typical take-out meal will also likely contain higher levels of fat, salt and sugar than are ideal for good health and body composition goals, and this can increase body fat levels.”

So, if you’re considering intermittent fasting for muscle gain because you think the diet lets you double down on pizza while staying on track with fitness goals, think again. You’ll still need to eat the same healthy foods after all.

Common questions about intermittent fasting and muscle gain

The stuff you really want to know.

1. Can you gain muscle while intermittent fasting?
Yes, building muscle while intermittent fasting is possible. That said, intermittent fasting definitely isn’t for everyone. You’ll need to not only continue training and consuming calories at full capacity, but also shape your lifestyle around small windows of eating. If it works for you, great, but don’t stress if it doesn’t, as research has shown that intermittent fasting muscle gain is largely identical to the muscle gain experienced by those who aren’t fasting.

2. What is the best intermittent fasting for muscle gain?
There are different ways to approach intermittent fasting and muscle building. More common methods include the 5:2 mode, in which you eat regularly five days a week, then have significant restrictions for two non-consecutive days; the 16:8 mode, in which you do all your daily eating within an eight-hour window then fast for the remaining 16 hours; and the Fast 800, in which you restrict yourself to 800 calories per day for two weeks and consume those calories within a window of 8-12 hours.

It’s difficult to claim that one of these methods is the best intermittent fasting for muscle gain. Again, whatever works best for your body should always be the top choice.

3. Is intermittent fasting bad for muscle growth?
Intermittent fasting could potentially be bad for muscle growth. If fasting means you’re not getting enough calories, your workout performance and recovery can slip, leading to fewer muscle gains. Quality of protein is key, too, so you need to make sure you’re prepared with the right kind of foods to promote muscle growth rather than eating whatever is on hand during your window.

Want more nutrition advice from the experts?

• 9 questions about intermittent fasting
• How to gain weight and muscle mass
• The 7 most common protein questions
• 5 power bars to boost your workout
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