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Intermittent Fasting and Bodybuilding: What Bodybuilders Need to Know


Intermittent fasting results primarily in fat loss and improved health due to calorie reduction and better insulin sensitivity, among other things. Meanwhile, a calorie surplus combined with resistance training and optimal protein intake is necessary for gaining muscle. With that in mind, you might be asking if intermittent fasting bodybuilding would work.

If you’re someone who regularly goes to the gym to pack on muscle but you also love fasting for all the benefits it provides, this article is for you. Here, we’ll explain how to do both while reaching your bodybuilding goals.

Can You Build Muscle with Intermittent Fasting?

The short answer to this is yes, building muscle is possible while incorporating intermittent fasts every now and then. For it to work, you need to keep in mind a few important rules of body recomposition — an approach where you lose fat and gain muscle at the same time.

One is the need for a small calorie deficit, which can be achieved by manipulating your macronutrients (e.g., carb restriction and upping protein and fat for those on a ketogenic diet), limiting processed foods, and intermittent fasting which is the main focus of this article.

These fat-loss strategies are then combined with a diet rich in protein, strength training, supplementation (when necessary), and recovery. A calorie excess, on the other hand, is necessary during the bulking phase of bodybuilding.

Since intermittent fasting cuts your calorie intake, it’s important to be careful to not do it excessively. You’ll probably be better off with shorter intermittent fasts — like a 12-hour or 16-hour fast. That way, you can eat enough calories to support muscle growth and testosterone production during your feeding window (*).

Should Bodybuilders Do Intermittent Fasting?

There is no definitive rule that people must practice intermittent fasting for bodybuilding, although fasting can benefit bodybuilders in many ways.

For example, intermittent fasting significantly helps with the fat loss phase in bodybuilding, also known as the “cutting” phase in which they try to get as lean as possible. This usually lasts about 2-4 months. Ultimately, bodybuilders end up losing body fat while keeping as much of their muscle mass as possible.

A 2011 review article noted that intermittent fasting was superior to daily calorie restriction in terms of preserving lean mass. While overweight and obese adults achieved similar weight loss and fat mass loss results, those who fasted didn’t lose as much fat-free mass as expected (*).

This is mostly why many bodybuilders, especially natural bodybuilders, turn to intermittent fasting mainly as a fat-loss tool.

As a bodybuilder and founder of Vitalized Future, Robb Harrison shares his experience: “I’ve done plenty of 16:8 intermittent fasting in my time and I’m always at my leanest when doing this.” Robb adds, “If I want to achieve a single-digit body fat percentage, then I’ll always use intermittent fasting as a useful tool.”

For those who do decide to fast, a good place to start is a 12-hour fast, which includes your sleeping hours — let’s say ending your last meal at 8 pm and fasting from 10 pm to 10 am the following day. This would make intermittent fasting less difficult for a beginner.

Once you adapt, you can slowly increase your fasting hours to 13 until you reach 16 hours.

How Intermittent Fasting Can Help Bodybuilders

In addition to fat loss and lean mass preservation, intermittent fasting for bodybuilders helps them become more mindful of their food choices. Since your eating hours are limited, you’d be making sure that anything you eat during your feeding window gets you optimal results.

Grass-fed beef, eggs, omega-3-rich fish, berries, nuts, and leafy greens are the best options for meeting your protein and micronutrient needs (vitamins and minerals) while boosting satiety. Conversely, you wouldn’t want to refuel with calories from unhealthy, highly processed foods — which are often empty calories.

Intermittent fasting is also a proven strategy to lower insulin resistance, which is linked to increased fat accumulation and muscle wasting (* , *).

A 2021 randomized controlled trial found that after 12 months of time-restricted eating, the subjects’ insulin sensitivity significantly improved. Their lipid profile also improved, including cholesterol, HDL, and LDL (*).

By becoming more insulin-sensitive, you set yourself up for bodybuilding success because, with insulin, glucose (from the foods you eat) can enter your cells to support muscle growth. Recall that insulin is the hormone that transports glucose to insulin-dependent cells, such as the muscle and liver.

Should Bodybuilders Workout Fasted?

Fasted workouts aren’t a must. While there are benefits to working out in the middle of an intermittent fast, not all bodybuilders choose to do them.

Those who are new to fasting, in particular, may find themselves suffering from low energy levels, which decreases their performance in the gym. Unless you’re fully fat-adapted, meaning your body can always tap into its stored fat to sustain your activity, expect your fasted workouts to be a bit challenging.

Additionally, you’re likely to be able to power through high-intensity interval training, lift heavier weights, and do longer workouts if you ate a pre-workout snack or meal that includes carbohydrates.

Julius Cermak, a Naturopathic Herbalist & Holistic Healthcare Practitioner who has worked with competitive athletes, says that though he’s a proponent of intermittent fasting, athletes are not medically advised to do it. He adds, “Technically, it won’t do you any tangible harm. But it will drastically set back your performance goals.”

Bodybuilders who opt to train in a fasted state usually do it for increased lipolysis so they get shredded sooner (*). For example, walking on the treadmill for 30 minutes first thing in the morning before breakfast.

If you plan on working out during intermittent fasting, it’s probably best to do the workout at the beginning of the fast, which is close to your pre-fasting meal. That way, you have enough fuel. Another option is to keep your exercise intensity low or the duration short.

How Long Should Bodybuilders Fast?

Different intermittent fasting variations exist, such as the 16:8 method where you fast for 16 hours, then eat within an 8-hour window. It’s the most popular fasting approach among bodybuilders and those who simply want to lose weight and get healthier.

12:12 is another type of fasting for bodybuilding where you forgo food for 12 hours, then eat within the remaining 12 hours. It’s easier and increases your chances of packing on more muscle because you have more time to consume enough calories.

For bodybuilding, keep in mind that longer fasts aren’t always better. This is especially true if you’re planning on building pounds of muscle in just a few months.

Being in a caloric surplus is extremely important for muscle gain, especially during a bulking phase. Also, this allows you to get the most out of your strength training sessions.

Travis Wells, a vegan bodybuilder, coach, and co-founder at Fit Movment mentions, “Bulking while intermittent fasting is tough, and I’ve had to work up to it. However, I like it way better for quality of sleep at night since my body is allowing me to sleep, and not in overdrive, digesting food.”

How Often Should Bodybuilders Fast?

It depends. For you to decide, first determine your purpose. Are you intermittent fasting for cutting or bulking? If you’re doing a bodybuilding cut, a daily 16:8 approach will help you get shredded in the shortest possible time.

According to TJ Mentus, an ACE-certified professional trainer and functional range conditioning mobility specialist, states that intermittent fasting is easier when cutting because “there’s less time during the day when you could potentially eat.”

Bulking While on Intermittent Fasting

Some people find it more challenging to put on muscle than others despite training aggressively. In the bodybuilding community, we call them ectomorphs or hard gainers. If this is you, keep in mind that intermittent fasting may make it difficult to eat enough.

Consider these tips to make the most out of your bodybuilding plan while fasting:

bulking while intermittent fasting

1. Avoid long intermittent fasts.

Forget 20 and 24-hour fasts. Stick with 12:12 and 16:8 intermittent fasts. These are the best methods because they allow you to meet your calorie needs while reaping the benefits of intermittent fasting, such as increased growth hormone, improved insulin sensitivity, and cellular repair (* , *).

Besides keeping your fasts short, you might want to reduce their frequency. If you fast daily during the cutting phase, reduce it to twice or once per week.

2. Monitor your calories and macros during your feeding window.

Calories and macronutrients play a huge role in the bulking phase. The more calories you provide and in the right macro proportions, the better your performance in the gym and muscle gains without putting on too much body fat.

Make sure to determine the calories you’ll need for weight gain. You can start with a calorie surplus of 5% and slowly increase it to 15% over a few weeks. For those who are naturally lean and have a difficult time gaining weight, you can start at a higher calorie surplus of 10%.

When it comes to macros, typical bulking diets are often high-carb, and understandably so. If you choose not to do low-carb or keto during bulking, your carbs will make up 40% of your total calorie intake, whereas fat sits at around 30%.

For those who choose a low-carb approach to bulking for personal and health reasons, increase dietary fat to 65%. Fat provides the most calorie per gram (9 kcal/g). This helps with your caloric surplus.

3. Prioritize your protein intake.

Protein is extremely important for maximizing muscle growth. It provides the amino acids needed for muscle fiber repair and growth.

Jesse Feder, a personal trainer, strength coach, and registered dietitian, recommends getting 1-2 grams of protein per pound of lean mass. “This will ensure you preserve as much muscle mass as possible and recover from your workouts,” says Feder.

Among the essential amino acids, the branched-chain amino acids (BCAAs) leucine, valine, and isoleucine are unique in that they induce an anabolic state. Not only do they boost muscle protein synthesis, but they also improve your endurance (* , *).

During your feeding window and non-fasting days, you can get these amino acids through supplementation (like whey protein and BCAAs) and foods like beef, chicken, fish, eggs, chickpeas, almonds, and pumpkin seeds.

4. Lift weights during your feeding window.

Working out fasted is probably not ideal when you’re bulking up. This is because, during intermittent fasting, your body enters a catabolic state where it utilizes stored nutrients.

If you lift weights in the middle of a fast, there’s a chance you’ll also be breaking down muscle — unless your main goal is to trim off excess body fat.

That said, lift weights during your non-fasting days or within your feeding window on fasting days where you’re storing nutrients to support growth.

5. Bulk up the healthy way.

Even when you’re in a calorie surplus, don’t take for granted the quality of your diet. This means eating clean by obtaining your calories from whole foods.

Steer clear of highly processed options, such as potato chips, french fries, muffins, cakes, and other sugary desserts. Clean bulking, as opposed to dirty bulking, is the best route for preventing excess fat gain and helping you maintain good health.

Intermittent Fasting Bodybuilding Sample Meal Plan

Below, we’ve provided a sample meal plan to give you an idea of what an intermittent fasting day looks like. Modify them according to your individual calories and macros, and your food preferences (e.g., clean vs dirty bulking, gluten-free, dairy-free, ketogenic, low-carb, etc.):

Pre-fast meal 

  • Baked chicken wings
  • Eggs and cheese
  • Stir-fried broccoli and baby carrots
  • Fresh fruit like strawberries

Start fasting at 8:00 pm

  • Water
  • Black coffee or tea
  • Calorie-free electrolyte drink

Post-fast meal after ending the fast at 12 noon the next day

  • Bone broth
  • Yogurt or cottage cheese
  • Wild salmon or mackerel
  • Sweet potatoes and other complex carbs

The Bottom Line

Contrary to popular belief, intermittent fasting can be a great tool for bodybuilding. Use it to increase fat loss during the cutting phase or avoid putting on too much body fat during the bulking phase.

Overall, fasting for bodybuilding boosts your health and longevity.

If you decide to test the benefits of intermittent fasting and bodybuilding, make sure you’re not restricting your calories too much to help you get those gains.

Keep your fasts short, optimize protein intake, and avoid training during your fasting window (unless you’re aiming for fat loss). While we haven’t discussed training recovery in this article, remember to prioritize it. Aside from eating properly, be sure to get enough sleep and reduce chronic stress.

10 References

Zamir A et al. Manipulation of Dietary Intake on Changes in Circulating Testosterone Concentrations. 2021 September 25

Varady K A et al. Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?. 2011 March 17

Wondmkun Y et al. Obesity, Insulin Resistance, and Type 2 Diabetes: Associations and Therapeutic Implications. 2020 October 9

Wang X et al. Insulin Resistance Accelerates Muscle Protein Degradation: Activation of the Ubiquitin-Proteasome Pathway by Defects in Muscle Cell Signaling. 2006 September 1

Moro T et al. Twelve Months of Time-restricted Eating and Resistance Training Improves Inflammatory Markers and Cardiometabolic Risk Factors. 2021 December 1

Kim T et al. Comparison of the effects of acute exercise after overnight fasting and breakfast on energy substrate and hormone levels in obese men. 2015

Hollstein T et al. Effects of Short-term Fasting on Ghrelin/GH/IGF-1 Axis in Healthy Humans: The Role of Ghrelin in the Thrifty Phenotype. 2022 August 18

Bagherniya M et al. The effect of fasting or calorie restriction on autophagy induction: A review of the literature. 2018 August 30

Wolfe R et al. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?. 2017 August 22

Kim D et al. Effect of BCAA intake during endurance exercises on fatigue substances, muscle damage substances, and energy metabolism substances. 2013 November 28


6 thoughts on “Intermittent Fasting and Bodybuilding: What Bodybuilders Need to Know

  1. Ive read and practice drinking coffee in the morning with coconut oil and grassfed butter as part of an intermittent fast (dinner to 2pm the following day). I wasnt sure how the practice technically qualified as ok for consuming during intermittent fasting time other than because there’s no carbs so there’s no subsequent spike in blood sugar. Does this philosophy “technically speaking” align with intermittent fasting?

  2. I’m not a bodybuilder. I’m a powerlifter. So looking muscular is not my ultimate goal, strength is my goal. I have been doing keto for 3 months now. I’ve dropped over 50lbs which is great. However I have lost a substantial amount of strength. Almost nothing I’ve read talks about increasing strength performance. Please address this in further post. I have added more protein into my diet to help and considering adding a carb drink after my lifts to help. Is there a better “keto” way. My ratio is still higher fat 56-35-9 (fat-protein-carbs)

  3. This article is poorly informed and has many errors. Let’s start with the fact that collagen is useless for building muscle. It’s utility lies in improving the structure of skin, hair, nails, bone, ligaments and so on. It contains insufficient amounts of BCAAs to be useful for building muscle and should be used additively rather than substitutively to a bodybuilding diet.
    Second, for the maintenance or enhancement of lean body mass, it is better to eat slightly less protein on weight training days and slightly more on rest days. Why? Because when training, there’s already an anabolic stimulus owing to the training which will make the utilisation of amino acids by muscle tissue more effective. On rest days, there’s no training as an anabolic stimulus, so dietary protein is the only anabolic stimulus and is needed in greater quantities to maximize muscle protein synthesis then when combined with training.
    I can’t remember off the top of my head what other errors or in your article, and I’m not prepared to re-read it, as I’ve read a lot of your articles and they are full of assertions which are not supported by science. It is not education but marketing. You’re not an expert but a salesperson.

    1. Hi Aaron, you may be correct in saying that collagen protein does not stimulate muscle protein synthesis but it does still play a role in the structure and function of muscle.

      Also as you mention the anabolic stimulus from training, it is important to note that studies that show what you are saying is in untrained populations. This same response to training is not found to the degree you are saying in more trained populations. This makes the need for protein different from person to person.

      I hope I was able to clarify this for you.

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