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Lifting Weights While Fasting: Is It a Good Idea?

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a young woman is flexing her bicep, holding a kettlebell in one hand, lifting weights while fasting
David J. Sautter post Reviewer David J. Sautter post Reviewer
Verified by David J. Sautter
NASM Personal Trainer, NASM Fitness Nutrition Specialist, ACE Sports Conditioning Specialist, NASM Performance Enhancement Specialist

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Have you ever considered hitting the gym on an empty stomach? The idea of lifting weights while fasting might sound daunting or even a bit extreme. 

After all, we’ve always heard that food is essential fuel for powering through any intense workout. But what if there’s more to the story than the traditional ‘fuel up to bulk up’ approach? 

If you’ve ever toyed with the idea of fasting before a workout, or even if it’s a completely new concept to you, you’re in the right place. 

From the potential hidden benefits that could boost your fitness routine to the important precautions you should consider, this article is your guide to understanding how and why lifting fasted might just work for you.

What Does It Mean to Work Out Fasted?

Contrary to popular belief, fasted training isn’t necessarily the same as lifting weights on an empty stomach. However, there is some overlap.

To be in a fasted state, you must avoid eating food for at least eight hours, or sometimes longer, depending on the composition and size of your last meal. It’s when your insulin levels are at baseline, and your body more readily taps into stored glycogen and body fat for the energy it needs.

In other words, your stomach might be empty, but that doesn’t necessarily mean you’re in a fasted state. An empty stomach is just one requirement.

For most people, working out in a fasted state means doing so in the morning before having breakfast. In some cases, it could also be part of an intermittent fasting protocol, where people don’t ingest any calories for 12 to 36 hours.

We’ll cover both cases below.

Can You Lift Weights Fasted?

Yes, lifting weights fasted is possible and even recommended by some experts for people who aim to lose weight. 

The idea is that by lifting fasted the body more readily taps into its fat reserves for energy, leading to greater fat breakdown.

In a 2014 paper by Schoenfeld, subjects trained in either a fasted or fed state, and both groups also followed a calorie deficit. The results showed similar weight loss and changes in body composition between the groups. [1]

Okay, but is lifting fasted detrimental to muscle gain? Fortunately, that’s not true.

In one study, researchers noted that muscle protein synthesis was elevated following resistance training (an indicator for growth and recovery), even in a fasted state. [2]

Plus, we should take into account that most trainees ingest protein after training, which kickstarts the recovery process and immediately slows down muscle breakdown rates. [3]

With that said, if your primary goal is hypertrophy (muscle growth), you should consider taking a calorie-free or low-calorie amino acid supplement to further protect lean muscle gains during weight training on an empty stomach.

Pros of weight lifting on an empty stomach or fasted

  • Enhanced fat-burning
  • Greater production of human growth hormone [4]
  • Potential boost in insulin sensitivity [5] 
  • Convenient for early morning training

Cons of combining weight lifting and fasting

  • Your performance might be impaired, at least initially
  • Greater fat-burning is unlikely to result in superior fat loss [1]
  • You might get quite hungry after a while
  • Some people report feeling lightheaded

Intermittent Fasting and Weight Lifting

Intermittent fasting is a nutritional strategy where people purposefully avoid all calories for specific periods of time, typically 12 to 36 hours. 

A popular example is the 16/8 fast, where folks don’t eat for 16 hours of the day and get all of their calories in an 8-hour window.

Another popular option is the 24-hour fast, typically done once or twice weekly. This approach is also known as Eat-Stop-Eat and was popularized by Brad Pilon.

A more extreme example (not recommended for beginners) is the 36-hour fast, also known as the Monk Fast.

Weight Training: Energy and Nutrient Demands

The body needs two nutrients for weight training: 

  • Protein to support recovery and limit muscle breakdown 
  • Carbohydrates to fuel physical activity and replenish lost glycogen [6]

To lift weights on an empty stomach would mean not having an immediate energy source and instead relying on glycogen and lipolysis (fat breakdown). It also means not having a steady stream of amino acids and instead depending on your body’s lean tissue.

At first glance, that might seem bad, but we must remember that it doesn’t necessarily mean we’ll experience a performance decrease or muscle loss.

For one, research suggests that the decline in performance most people experience is more so the result of morning neuromuscular deficit. [7] 

In other words, a lack of fuel likely isn’t the problem. It’s the change in the time of day when the person trains (e.g., the morning instead of the afternoon or evening).

Second, rather than obsessing over short-term changes in performance or how the body gets the energy it needs, it’s much better to look at long-term results. 

As discussed above, fasted and fed training lead to similar body composition changes. [1]

So, what does that mean for you? 

You might experience a temporary but minor reduction in performance if you switch to fasted training. That said, you should adapt within a few weeks and things should return to normal.

To avoid having to adapt, you can move your workouts to a time of day when you’ve already had a meal or two. For instance, instead of lifting on an empty stomach in the morning, train in the afternoon or evening after having a meal or two.

That way, you’ll have more energy for lifting and an amino acid supply to kickstart recovery and limit protein breakdown during and after working out. [8]

Prolonged Fasting and Weight Lifting

Prolonged fasting, typically when people don’t consume calories for 20+ hours, is slightly different and carries more risks. Let’s look at some of its effects:

  • Energy levels – not getting any calories for 20 or more hours can lead to low energy levels and muscle weakness.
  • Muscle protein synthesis – a lack of protein for extended periods can hinder protein synthesis, increase the risk of tissue breakdown, and impair recovery. [9]
  • Dizziness – some people experience dizziness and lightheadedness as a result of not eating for extended periods of time.

On the whole, long fasts can impede weight training performance, especially if the eating window is too short and the person struggles to get enough calories and protein.

When Do You Start Losing Muscle While Fasting?

Research suggests that three weeks of not working out won’t necessarily lead to muscle loss. [10] 

However, things are different for people who fast for long periods and don’t get the energy and nutrients they need to support lean tissue.

Unfortunately, how quickly someone starts losing muscle is unclear and likely dependent on the duration of the fast, what the person eats during feeding windows, and whether they engage in resistance training.

In the short term, there doesn’t seem to be a risk. Even if protein breakdown occurs more quickly during a 14- to 20-hour fast, research suggests that intermittent fasting combined with resistance training generally helps people maintain or even build muscle. [11]

However, some factors that increase the risk of muscle loss while fasting include:

  • The fast extends beyond 20 hours.
  • The person works out fasted, which may lead to lethargy, dizziness, and muscle weakness.
  • The person can’t eat a post-workout meal rich in protein. [8]
  • The person struggles to get the bare minimum of 0.8 grams of protein per pound during each feeding window. [12]
  • Fasting causes the person to lose weight rapidly, over 0.5 to 1 percent of their body weight per week. [13]

How to Fast if You Lift Weights

As someone interested in health and fitness, you’re probably curious about the many proven benefits of fasting and want to experience them for yourself. However, lifting weights while fasting can be challenging.

Fortunately, there are ways to combine the two for excellent results. 

Your best option is to go for a milder fasting regimen, such as:

  • 12/12 – fast for 12 hours each day
  • 10/14 – fast for 14 hours a day and get your calories in a 10-hour window

You could also try a 24-hour fast once a week. However, we recommend doing the fast on a rest day to reduce the risk of a performance drop or impaired recovery.

For instance, if you lift from Monday to Saturday (check out our guide on lifting daily and whether we think it’s a good idea), do the fast from Saturday evening (following your high-protein post-workout meal) until Sunday evening.

Working out on days you choose to fast is okay, but it’s best to time your workouts in a way where you can:

  • Have at least one meal before training.
  • Eat shortly after working out if you train fasted.

For example, let’s say you follow the 10/14 fast and eat from 10 in the morning until 8 PM.

In such a case, it’s best to work out from noon onward, ensuring you’ve had at least one meal and enough time has passed so you don’t experience stomach distress. Alternatively, work out from 9 to 10 AM and break your fast soon after.

Bottom Line

Lifting weights while fasting can be tricky but it’s not necessarily a bad idea if you do it right. 

Let’s do a brief recap:

  • An empty stomach is necessary for a fasted state; however, the two aren’t necessarily the same.
  • Actual fat loss doesn’t seem to be greater for people who train fasted.
  • You can lift fasted so long as it doesn’t impair your performance (it’s different for everyone).
  • If you want to train fasted, eat a high-protein post-workout meal soon after.
  • Combine a milder fasting protocol (e.g., 10/14 or 12/12) with weight training to reap the benefits.
  • Fasts that keep you from getting enough protein, lead to excessive weight loss, impede your training performance, and last for 20+ hours put you at risk of muscle loss.
Disclaimer This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!

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