5 Important Facts About Working Out and Intermittent Fasting

Man lifting weights while intermittent fasting

Working Out While Fasting is OK – As Long As You Do It The Right Way

Eating the right foods is a crucial component to working out and physical fitness, but if you’re fasting, you’re not eating. So, that being the case, it would only make sense that exercise and fasting would have to be a bad combination, right?

As it turns out, not necessarily – as long as you’re doing it the right way.

Intermittent fasting is a type of scheduled eating where you only eat during certain hours of the day, or only on certain days of the week, while abstaining from food during the other times. People choose to practice intermittent fasting because of its weight loss effects, health benefits, or merely to simplify life and reduce grocery bills.

There’s been a lot of research that shows how intermittent fasting can produce dramatic positive changes in the body, and could even extend a person’s lifespan (1).

Smart Steps to Follow When Working Out While Intermittent Fasting

If you’re going to capitalize on the fat loss aspects of IF while building muscle at the same time, you’ll need to approach it in a strategic way and plan around your eating and fasting periods.

Here are four key points to keep in mind when combining exercise with intermittent fasting.

1. Plan on Maintaining Muscle When Fasting, Not Building it.

No matter if you’re eating during an 8-hour window each day, or fasting twice a week, or some other form of intermittent fasting, you will more than likely experience weight loss. One reason being that it’s a lot more difficult to overeat when you’re consuming your daily caloric intake in a relatively short period of time.

This is why intermittent fasting is considered such a great way to lose weight, since by cutting back the amount of time during which you can eat, you’re also cutting back on the amount of calories you’ll consume.

That said, if you’re primary aim is to increase muscle mass, then fasting won’t be a good option. Most people aren’t going to be able to build muscle while following a calorie-restricted diet (2).

You might gain a little, but it won’t be much compared to the gains you would get while increasing your daily caloric intake. So, when you’re fasting, you’re main priority should be burning fat and maintaining muscle mass, not building it.

Main Takeaways:
  • If you follow an intermittent fasting plan you will more than likely experience weight loss, since it is a type of calorie-restricted diet.
  • However, increasing muscle mass while intermittent fasting is not really feasible; instead, you should focus on preserving muscle mass and burning fat.

2. Keep Lifting Those Weights

Even though burning fat may be your primary aim , it’s still important to keep lifting in order to prevent your body from consuming muscle for fuel. Although you probably won’t gain much muscle mass while fasting (if any), as long as you’re lifting, you’ll at least keep the gains that you already have (3).

Doing the same exercises to build muscle when you’re not fasting will help to preserve more muscle when you are. And because you’re mainly trying to maintain muscle mass, not increase it, you won’t have to go with your normal full-on workout schedule.

You can probably get by with a light full-body workout two or three days a week to keep that muscle mass intact.

Main Takeaways:
  • Exercise is important while intermittent fasting to maintain muscle and prevent it from being used by the body for fuel.
  • Doing light full-body workouts 2-3 times per week should be enough to maintain that muscle mass.

3. Make Sure to Eat Before You Work Out

Whether you’re lifting, running, doing CrossFit, or any other form of intensive exercise, the body needs to be fueled with carbohydrates. If you engage in these types of training while you’re fasting, you’ll notice a serious lack of progress. Rather than improving performance and fitness, you’ll very likely accomplish just the opposite (4).

If you’re overweight and trying to drop some pounds, then exercising while fasting will probably be OK, since your main goal is to lose weight, not necessarily build muscle.

However, if you’re on the thin side, or otherwise concerned about conserving muscle mass, you’ll definitely want to plan on working out during your eating periods, or schedule your workouts soon after your eating window has closed, since the calories, carbs, and protein will help fuel your workout and aid in recovery.

Main Takeaways:
  • Doing high intensity exercise while fasting may lead to poor performance.
  • If you are concerned about preserving muscle mass, plan on working out either during, or after, your eating window.

4. Do Your Cardio Workouts While Fasting

Touted by sports athletes and celebrities, as well as bodybuilders as a method for “cutting”, these days there are a lot of people who swear by doing “fasted” cardio. Typically, this form of workout is done in the morning before breakfast, or otherwise when the body is still in a fasting state (5).

Although the evidence to support how much more effective fasted cardio might be at burning fat is unclear, there’s no reason you can’t try it. As long as you don’t overdo it, it only makes sense that you might actually burn more fat while doing cardio in a fasted state.

Either way, loading up on carbs before doing less intensive training is less important than when you do more intensive activities, such as lifting. This is because slower cardio and other less-intensive activities are mainly fueled by fat.

Main Takeaways:
  • Fasted cardio is typically done in the morning, before breakfast, on an empty stomach.
  • Research is unclear if fasted cardio is more effective at burning fat, but hasn’t shown any negative effects either.
  • When exercising in a fasted state, avoid doing high intensive workouts and stick with slower cardio, since less intensive workouts are mainly fueled by fat.

5. Take the Right Supplements

During fasting periods it’s vital to avoid eating foods or drinks containing calories, but what about supplements? If you’re working out while fasting it’s a good idea to take supplements in order to keep up your levels of vitamins, minerals, and other nutrients.

However, some supplements can break your fast, but others have no effect on it – so it’s important to know which ones to avoid. These include any supplements that can trigger digestive function or spike your insulin levels, causing you to break your fast and kicking you out of ketosis.

Additionally, some supplements are fat soluble, meaning they won’t necessarily break your fast, but are meant to be taken with food. If you take them on an empty stomach they’ll pass through your body without providing much benefit at all.

On top of that, certain supplements can also make some people nauseous or cause stomach upset if taken without food.

Here are a few examples of supplements you can take when working out in a fasted state:

See Also: Which Supplements Can You Take While Fasting?

Working Out While Intermittent Fasting – The Final Word

Even though lifting weights during a fasting period is not a good idea, doing cardio in a fasted state is OK, and could actually help you burn off even more fat. Just remember to do the lifting during your eating window or after, and your cardio before you eat.

See Also:

Physically fit man


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3946160/
  2. https://peterattiamd.com/can-you-maintain-muscle-during-fasting/
  3. https://www.healthline.com/nutrition/intermittent-fasting-muscle
  4. https://www.ncbi.nlm.nih.gov/pubmed/29315892
  5. https://www.health.com/fitness/what-is-fasted-cardio
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