Intermittent Fasting and Strength Training: Can You Build Muscle While Fasting?

What Is IF | Strength Training & IF | Building Muscle | Training While Fasted | Tips | Post Workout Nutrition

Intermittent fasting (IF) has gained popularity over the years for its ability to improve health and help with weight loss.

When practicing IF, adding strength training into the mix is one of the best things you can do, no matter what your goal. Read on to learn why combining fasting and strength training is essential, and how to fasted weight training safely.

Intermittent fasting is an eating pattern where people only eat within a short window of time each day, choosing to fast the rest of the time. Popular forms of intermittent fasting include:

• OMAD (one meal a day): all calories are consumed in one sitting, with the remaining 23 hours a day fasted

• 16/8 method: 16 hours of fasting, eating as normal over 8 hours

• 5:2 diet: eating as normal for 5 days, with 2 days per week completely fasted or under 500 calories

Intermittent fasting is typically adopted to help with weight loss as reducing the period you can eat in can help with reducing calories consumed across the day. Reducing the number of meals that you eat can make dieting easier as there is less to think about too.

There are also non weight loss benefits to IF, including reduced insulin sensitivity, improved cholesterol and blood pressure, and improved metabolic function.  

There are some potential downsides to intermittent fasting, such as excessive hunger, preoccupation with food and binge eating, as well as headaches, mood swings, insomnia, and digestive issues. It is recommended to speak to a medical doctor before attempting this pattern of eating, especially if you have diabetes, are pregnant, or have had an eating disorder.

The short answer is yes - and in fact not only can you combine intermittent fasting and weight training, but you should do.

Some studies have found that intermittent fasting can lead to a decrease in lean muscle mass. IF pushes the body to use stored glycogen for fuel. This initially comes from glycogen stored in the liver but can also be taken by breaking down muscle cells to use muscle glycogen, causing muscle loss over time. Losing muscle leads to poorer metabolic health and a high body fat percentage even at a low weight, causing a 'skinny fat' appearance.

In addition to the many benefits of weight training, strength training while fasting helps to protect against muscle loss by stimulating muscle protein synthesis to counteract this muscle breakdown.

Other benefits of combining IF and strength training include:

• Higher fat burn. Weight training fasted burns more fat as the body's glycogen stores are depleted. Studies have found that combining weight training and IF lead to decreased fat mass, rather than muscle mass.  

• Body composition. Combining IF and strength training can help with weight loss while maintaining lean muscle, improving overall body composition.   

• Improved insulin sensitivity. Strength training helps muscles to absorb glucose, and intermittent fasting helps with insulin resistance. Combining both is a great way to improve your insulin sensitivity and efficiency.

While these are some great benefits, there are some downsides to intermittent fasting training too.

• Increased muscle breakdown. Although adding strength training can help to prevent muscle breakdown from IF, fasted training can increase the risk of the body using muscle for fuel. Not getting enough calories or protein further increases this risk, which can happen when intermittent fasting.

• Reduced energy and performance. Training while fasted means your body's energy stores are low which can make it harder to workout. Some people find they have reduced strength and endurance when doing intermittent fasting strength training, which can limit the progress they make in the gym.

Building muscle is possible while intermittent fasting, but it can be more challenging for a few reasons. To build muscle mass, the body needs a surplus of calories. This can be more difficult to achieve when intermittent fasting as there is less time available to consume calories in.

Another challenge is that eating protein regularly across the day has been thought to be more beneficial for building muscle than eating large quantities at once. This can again be more challenging to do when fasting for periods over the day. Some forms of intermittent fasting, such as the 5:2 diet, may be more beneficial for building muscle as it allows for more regular eating and higher calorie intake for some days.

Training fasted can also make it harder to build muscle if energy and performance are impacted. The muscles need to be given enough stimulus to warrant muscular hypertrophy. If training on an empty stomach means you do not have the energy and power to create enough tension on the muscles, this can limit hypertrophy.

Fasted training refers to waiting at least 6 hours between eating and training, so you can combine strength training and intermittent fasting without weight training on an empty stomach by training within your eating window.

Deciding whether or not to train fasted depends on a few factors:

• Fitness goals. If your primary goal is to lose weight, training fasted can be a good option. If you fast for the health benefits but you want to build muscle or strength, you'll likely benefit more from training during your eating window.

• Energy levels. Some people enjoy fasted training, finding they have increased mental focus and energy, while others can feel sluggish and suffer with low energy. If you struggle to get a good workout while fasting, you might see better results training once you've eaten.

• Workout type. Low to moderate intensity workouts can work fasted, but for higher intensity training sessions where the body prioritises glucose for energy, it's generally best to work out once you have eaten.

Combining IF and strength training can have great benefits to your health and weight, especially when done in a way that limits negative effects.

Timing your workouts around your fasting can help to limit side effects. If you prefer to train fasted, consider breaking your fast after your workout so you can replenish your glycogen stores and get in some protein. This should help to prevent muscle breakdown.

You can also work out during your eating window. This is a particularly good option if you struggle with low energy when training fasted.

It’s important to avoid high intensity workouts when fasting. Stick to low to medium intensity workouts when training fasted, keeping your high intensity sessions for when you’ve eaten.

It can be tempting to reduce your calories significantly when intermittent fasting but you should avoid creating too big a calorie deficit as this will reduce make muscle loss more likely. If you are trying to lose weight, stick to around 250-500 calorie deficit from your TDEE and get plenty of protein and carbohydrates in during your eating window. If you are not aiming to lose weight, make sure you are fitting in your maintenance calories during your eating window.

Staying hydrated is always important, but even more so when you’re fasting for a large portion of the day as we usually get water from the food we eat. Make sure you are drinking water regularly and are getting plenty of electrolytes such as magnesium and potassium from your foods when you do eat.

If you are new to IF, don’t jump straight into the deep end with long fasts and intense workout sessions. Start with a 10-12 hour fast, gradually moving up to 16 hours over the course of 1-2 weeks to help your body get used to burning fat for fuel. You can begin with low to moderate intensity workouts and gradually increase the intensity as your body adapts to fasted workouts.

If you are training fasted, post workout nutrition becomes even more important than normal. Aim to eat within a few hours of your workout, with meal should containing plenty of complex carbohydrates to refill your body's glycogen stores, as these will have been depleted through fasting and through exercise. Protein rich foods are also incredibly important, as these provide the protein to repair and rebuild muscle that has been broken down.

Examples of post workout meals to break your fast could be:

• Smoothie made with protein powder and fruit (like our green protein smoothie)

• Chicken and rice bowl (like this peanut chicken power bowl recipe)

• Breakfast burritos

• Steak and egg bibimbap  

Intermittent fasting isn't for everyone. While there are benefits from this style of eating, some people may find better results eating more regularly. If you do fast, performing strength training and prioritising high quality nutrition can help to prevent negative impacts of fasting and further improve your health.

Looking for a place to start your strength training? Find your nearest gym here.