Working Out While Fasting: How To, Benefits, And Tips

Low-Intensity Steady State (LISS) is ideal for working out while pursuing weight-loss goals because it relies primarily on fat for fuel, sparing muscle glycogen (20).

Exercise Execution Instructions

Proper form is non-negotiable, especially when fasted, as fatigue can set in differently.

Goblet Squat

1. Stand with feet shoulder-width apart, holding a dumbbell or kettlebell close to your chest with both hands.
2. Engage your core and keep your chest lifted.
3. Lower your hips back and down as if sitting into a chair, keeping your weight in your heels.
4. Descend until your thighs are parallel to the floor or slightly lower, ensuring your knees track over your toes.
5. Drive through your heels to return to standing, squeezing your glutes at the top.

Dumbbell Walking Lunge

1. Stand tall, holding a dumbbell in each hand by your sides.
2. Step forward with your right leg, lowering your hips until both knees are bent to approximately 90 degrees. The back knee should hover just above the ground.
3. Keep your torso upright and core engaged.
4. Push off your right foot to bring your left foot forward into the next lunge step.
5. Continue alternating legs for the prescribed reps.

Push-Ups

1. Start in a high plank position with hands slightly wider than shoulder-width apart.
2. Engage your core and glutes to maintain a straight line from head to heels.
3. Lower your body until your chest nearly touches the floor, keeping your elbows at a 45-degree angle to your torso.
4. Push through your palms to return to the starting position.

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Romanian Deadlift (Dumbbell)

1. Stand with feet hip-width apart, holding dumbbells in front of your thighs, palms facing your body.
2. Keep your knees slightly bent (do not lock them).
3. Hinge at your hips, pushing your glutes back as you lower the weights toward your shins. Keep the weights close to your legs.
4. Lower until you feel a stretch in your hamstrings, keeping your back flat and spine neutral.
5. Drive your hips forward to return to the standing position, squeezing your glutes.

Plank

1. Lie face down, then prop yourself up on your forearms and toes. Elbows should be directly under your shoulders.
2. Keep your body in a straight line from head to heels. Avoid letting your hips sag or pike upward.
3. Engage your core, quads, and glutes intensely.
4. Hold this position while breathing steadily for the designated time.

Can Beginners Safely Try Working Out While Fasting?

Yes, beginners can try working out while fasting, but caution and gradual progression are essential. If you are new to both fitness and fasting, diving into a 16:8 intermittent fasting morning workout immediately might be overwhelming.

When you are new to fasting, your body is not yet “fat-adapted.” Most bodies get used to having a steady supply of glucose. Suddenly removing that fuel source and adding exercise stress can lead to hypoglycemia (low blood sugar). 

Symptoms include dizziness, shakiness, lightheadedness, nausea, and extreme weakness (21).

Strategy for Beginners:

1. Talk to your healthcare provider: Make sure both fasting and the exercise you want to do are safe and appropriate for you.
2. Start with fasting on its own. Establish your 16:8 or 12:12 fasting routine for 1-2 weeks before adding fasted workouts.
3. Hydrate: Drink water and consider electrolytes (sodium, potassium, magnesium) before your workout. Fasting causes your body to flush out water and salts (22).
4. Lower Intensity: Begin with walking or light yoga. See how you feel.
5. Listen to Your Body: If you feel dizzy, stop immediately. It takes time for your metabolic machinery to upgrade. Have a small snack and see how you feel. You can still lose fat through exercise and healthy eating habits. Remember that fasting is a tool, not the main reason for fat loss.

It is crucial to avoid common pitfalls when starting. You can learn more about what not to do in our guide on intermittent fasting mistakes.

Does Exercising While Fasting Burn More Fat?

This is the most common question, and the answer requires nuance.

During the workout: Yes. As mentioned earlier, exercising in a fasted state increases the percentage of energy derived from fat oxidation during the session. Because insulin is low and glycogen is preserved (to an extent), the body mobilizes free fatty acids from adipose tissue (23).

Over 24 hours: Not necessarily. This is where the concept of total energy balance comes in. If you burn more fat during your workout but then compensate by eating more calories later in the day, or if your overall activity decreases because you are tired from the fasted session, your net fat loss may not change.

Research has shown that for fat loss, the total calorie deficit matters more than whether you trained, fed, or fasted (24).

Think of fasted training as a way to “teach” your body to be a better fat burner (metabolic efficiency), rather than a magic trick that bypasses the laws of thermodynamics.

Read more: 20-Hour Fasting Diet: Everything You Need to Know Before Attempting This Intermittent Fasting Plan

Can I Build Muscle While Fasting?

Building muscle (hypertrophy) while fasting is possible, but it is not the most optimal state for maximum growth. 

Muscle growth requires 2 main things:

1. A sufficient training stimulus (tension)
2. Adequate nutrients (protein and energy) to repair the damage (25).

When you train fasted, you are in a catabolic (breakdown) state. To switch to an anabolic (building) state, you must break your fast post-workout with adequate nutrition (26).

The Key is Timing:

If you perform a 16:8 intermittent fasting morning workout, you must ensure your eating window provides enough total protein (approximately 1.6 grams per kg of body weight, or roughly 0.7 grams per lb of body weight) and sufficient calories to support recovery (27).

For those working out while fasting for 24 hours (OMAD or longer), muscle building becomes significantly harder. The window for getting the necessary nutrients is very small, and protein synthesis rates may be capped. If hypertrophy is your main goal, shorter fasts (like 16:8) are far superior to prolonged fasting protocols.

How To Avoid Losing Muscle When Fasting?

The fear of “burning muscle” is largely exaggerated, but it is a valid concern if you are not careful. Your body prizes muscle tissue and will generally try to protect it unless you are in a severe calorie deficit or completely sedentary.

Here are the research-informed strategies to preserve lean mass:

• Keep Resistance Training High: The most powerful signal to your body to keep building muscle is using it. You must lift weights (28). 

If you stop training, your body views that muscle as expensive tissue it doesn’t need to maintain.

• Prioritize Protein: When you do eat, protein is paramount. Aim for at least 20-25g of high-quality protein (29) immediately when breaking your fast to spike muscle protein synthesis.

• Avoid Excessive Cardio: Hours of fasted cardio can chronically elevate cortisol levels, which can be catabolic (30). Stick to the benefits of exercise while fasting in moderate cardio or HIIT, rather than marathon sessions.

• Stay Calorie Aware: Do not starve yourself during your feeding window. If your deficit is too large (>25-30% below maintenance), muscle loss is inevitable regardless of your workout timing.

If you find yourself plateauing or feeling weaker, you might be encountering workout problems related to under-fueling.

Frequently Asked Questions

• Does fasting burn fat or muscle first?

Fasting prioritizes burning glycogen (stored sugar) over body fat; some muscle protein is converted to glucose, but muscle tissue is generally preserved unless the fast is prolonged (several days) or body fat percentage is extremely low (31).

• Who should avoid fasted cardio?

Individuals with a history of hypoglycemia, pregnant women, those with eating disorders, and high-performance athletes requiring maximum glycogen availability for competition should avoid fasted cardio.

• Is it okay to lift weights while fasting?

Yes, it is okay to lift weights while fasting (32). Focusing on moderate reps and staying hydrated are key to safety and performance. However, some people find they don’t see the gains or performance improvements they aim for when lifting weights without adequate fuel.

• What should I not do after fasting?

You should not break your fast with highly processed, sugary foods or a massive binge meal, as this can cause a rapid insulin spike and digestive distress (27). Aim for a balanced meal of easily digestible, nutrient-dense foods. 

The Bottom Line

Working out while fasting can be a powerful strategy for those looking to optimize metabolic flexibility and simplify their fitness routine. It is not a magic pill, but rather a lever you can pull to enhance fat oxidation and improve insulin sensitivity.

By understanding the distinction between fasted and fed states, and by choosing the right exercise intensity–like the strength and cardio plans outlined above–you can reap the benefits of exercise while fasting without sacrificing muscle or performance.

Remember, the best fitness protocol is the one you can sustain. Whether you are doing a 16:8 intermittent fasting morning workout or occasionally experimenting with working out while fasting 24 hours, listen to your body.

The most important thing is consistency, so if it works better for you to fuel up before exercise, then do that.

Start slow, prioritize protein in your eating window, and treat your training with the respect it deserves. Your body is an adaptable machine; give it the right inputs, and it will give you the results you want.