Intermittent Fasting for Bulking: Can You Add Muscle While Fasting?

Written by Stephen Anton PhD on July, 1st 2021

Can you bulk up while practicing intermittent fasting? That is an interesting question, and one that many body builders and fitness enthusiasts have been asking as the popularity of intermittent fasting continues to increase.

The good news is the answer is 100% YES. That is, if the right stimulus is given to the body at the right times of the day.

Before discussing the intermittent fasting bulk plan, let’s first review what is typically recommended to someone who desires to “bulk up.”

Problems with Current Bulking Strategies

Up until recently, it was thought that the only way to “bulk up” is to eat frequent, large meals over the course of the day, while also pushing heavy weights around at the gym a few times a week. If your goal is to gain weight (both fat and muscle) as rapidly as possible, this approach does indeed work.

If on the other hand, your goal is to gain muscle without the added fat that typically accompanies the “bulking” phase, then it’s good to be aware of a couple downsides to this approach.

1. Unhealthy

First, the recommended eating plan during the bulking phase is unhealthy. Frequent and excessive food ingestion is damaging to the body because it leads to metabolic shifts that promotes unhealthy weight gain, particularly when combined with a sedentary lifestyle or infrequent exercise program. This is because every time you eat, a number of metabolic and hormonal changes occur that either instruct your body to work for you (i.e., use ingested calories and stored fat for energy) or work against you (i.e., store fat and gain weight). Of course, the timing of meals is really important as discussed below.

2. Counter-Productive

After the bulking phase is completed and sufficient weight has been gained, you have two potential options.

First, you can try to lose the fat that was gained during the “bulking” phase through strict dieting. This is counter-productive at best, as it’s unlikely you will lose all of the fat and retain all of the muscle that was gained during the bulking phase, with the result being that your body composition ends up not being too much different from the starting point. At worst, this approach could damage your tissues and organs, as the stress placed on the body during both the “bulking” and “cutting” phases can be quite high.

3. Excess Body Fat

A second option is to just stay bulky and carry a higher percentage of body fat than would be ideal from a health standpoint. If your sport is power lifting or sumo wrestling, then the extra weight may be advantageous but for almost everyone else, there is little benefit to carrying extra body fat (lean muscle is another story).

Intermittent Fasting Bulking Plan

In contrast to the traditional bulking approach, with the slow and steady IF bulk plan you can add muscle without gaining too much (or any) additional body fat. With this approach, the body is able to slowly gain muscle in a way that it can be retained, while keeping body fat levels low the whole time. The result is that you can craft the body you want, while looking and feeling good, throughout the whole process. If this is your goal, then the IF bulk approach is for you!

What Is the IF Bulk Approach?

Essentially, this approach combines a popular form of intermittent fasting, called time-restricted eating, with a muscle building diet and exercise program, to maximize muscle gain while minimizing fat gain, as you bulk up to your desired size (of muscle).

Another way to think of it is that this approach involves mimicking the traditional “bulking” and “cutting” phases BUT does so on a daily basis, and in a much healthier way. By breaking the day up into “cutting” and “bulking” periods, you can simply adjust the timing or amount of time of each window in accordance with your goals. For example, if the goal is to bulk more, than the eating window can be expanded so that more food can be consumed during the window.

Intermittent Fasting Bulking Benefits

From a health and muscle gain standpoint, there are a number of reasons to combine intermittent fasting, specifically time restricted eating, with a muscle building diet and exercise program:

1. Healthier Cells

First, intermittent fasting helps your cells become healthier, which can reduce toxic load. During fasting, the process that your cells use to eliminate waste products, called autophagy, is activated. This means you are cleaning out the “junk” when you are fasting, and this process appears to be critical to the survival of every cell in your body and has been linked to lifespan.

In fact, the Noble prize was awarded to a researcher in 2016 for the discovery of autophagy and the connection between this cellular quality control process and virtually every aspect of our health.

2. Improved Muscle Maintenance

What’s more, the process of autophagy is actually required to maintain muscle mass. When autophagy was intentionally prevented in rodents, their muscles quickly atrophied and they became weak. This is actually not all that surprising when you think about it, since we know the importance of sleep to muscle growth, and for most people sleep is the time when autophagy is highest!

Findings such as this strongly suggest that any impairments in the cellular quality control system can accelerate the process of muscle degradation!! Not only that, but when this cellular quality control process is not functioning efficiently, your metabolism can actually slow down, which can set you up for unhealthy weight.

3. Higher Quality Muscle Growth

For most people practicing the traditional bulk plan or unhealthy lifestyle, this process is unfortunately not very active. This means that the muscle gained may be of low quality (fat and muscle rather than pure muscle). Unfortunately, as we age this type of eating pattern can lead to increased abdominal fat and muscle loss. Once accumulated, this excess body fat can further disrupt cellular quality control processes and set up a viscous cycle of fat gain and muscle loss.

On the other hand, when you practice intermittent fasting, your cells become healthier. And healthier functioning cells means that there are less “bad guys” around, which allows your body to use more of its resources to repair and recover from workouts rather than fighting off the “bad guys.”

4. Increased Human Growth Hormone

Intermittent fasting can improve your body composition by training your body to use its own fat for energy and, over time, lose that stubborn abdominal fat. But what is less well known is that intermittent fasting can also help you gain muscle mass.

One of the reasons for this is that during fasting and exercise, your body secretes more growth hormone, which in turn helps you preserve your muscles and burn more fat. So, intermittent fasting, is a great way to get more growth hormone and improve our body composition.

Intermittent Fasting Bulking Research

Recent trials suggest that at a minimum intermittent fasting does not lead to muscle loss when combined with weight lifting.

The Experiment

For example, in a recent study, 34 healthy men were randomly assigned to either a normal control diet or daily Intermittent Fasting (16 hours of daily fasting) and followed for two months during which they maintained a standard resistance training program, the men in the Intermittent Fasting Group showed a reduction in fat mass (compared to normal diet) but no loss of lean mass or maximal strength.

The Results

Based on these findings, the scientists concluded:

“Our results suggest that an intermittent fasting program in which all calories are consumed in an 8-h window each day, in conjunction with resistance training, could improve some health-related biomarkers, decrease fat mass, and maintain muscle mass in resistance-trained males.”

How to Bulk While Intermittent Fasting

As great as these findings are, I believe you can do even better and pack on high quality muscle by focusing on consuming calories during the natural anabolic windows that occur when you practice both intermittent fasting and strength training.

The First Anabolic Window

The first anabolic window occurs immediately following your 14-16 hour fast. During this time, a metabolically healthy body has utilized its glucose/glycogen supply and is burning fat for energy, which means the body is very sensitive to insulin and other growth signals at this time. This combination of factors sets you up for a large anabolic response to your first meal.

The Second Anabolic Window

The second anabolic window happens during the post-workout time period, typically the dinner meal, presuming you train in the afternoon and/or early evening. After this workout, you get a huge insulin response at the time when your muscles are primed to absorb glucose to repair and regrow. So, during this post-workout anabolic window, almost all the glucose from carbohydrates is used by your muscles and does not stay in your blood stream for long.

This means the post-workout meal is the time to eat however many carbs and proteins as you want. Keep your fats low, but you can really enjoy eating lots of calories during your post workout meals. Keep the rest of your meals big, but lower in carbs. This will likely lead to a break in your macros, which, to be honest, is fine. If you’re going above and beyond with your carbs and protein in your post-workout meal, and your goal is to gain muscle, you’ll be fine.

The Post-Training Anabolic Window

If your preference is to train in the morning, all is not lost. While you will not have two anabolic windows, your post-training anabolic window will be HUGE! That is, if you have fasted and/or had only amino acids before your morning training session. If so, then the next meal you eat will be critical to your muscle building success and should primarily consist of liberal quantities of carbohydrates (both simple and complex) as well as some lean protein.

Bonus: Train Twice Per Day

Another option if you want to accelerate your results even faster is to train twice a day, once in a fasted state at the end of the fasting period and then again close to the end of the eating window. This is an advanced method and should only be done if you are fasted adapted and have trained in a fasted state before. But if the goal is to maximize muscle gain while keeping body fat stores low, this approach can produce incredible results.

If your schedule does not allow two workouts a day, that is completely fine as great results can be obtained through the combination of fasting and working out once a day, provided you follow the general recommendations above of consuming your larger meals during the body’s natural anabolic windows.

Intermittent Fasting for Bulking Summary

Overall, fasting and bulking can be combined successfully. In fact, compared to standard bulking approaches, intermittent fasting and bulking is healthier, more effective, and produces less body fat.

With intermittent fasting and bulking, you will also experience healthier cells, improved muscle maintenance, higher quality muscle growth, and increased human growth hormone.

In order to maximize your results, remember to focus calorie consumption during your natural anabolic windows.

For most people, that means in the beginning of the day when you first break your fast, and right after your evening workout.

More on intermittent fasting:

Does Coffee Break a Fast?

Intermittent Fasting Immune System: The Boosting Effects of Fasting


Dr. Anton

I’ve had the privilege of studying the fields of obesity, metabolism, and aging for the past 20 years and felt an increasing desire to share what I’ve learned with as many people as possible the past few years.

More About Dr. Anton

Real science. Real advice. Straight to your inbox!

Get the latest news on topics like intermittent fasting, healthy aging, reducing obesity, and more.


    Dr. Anton

    I’ve had the privilege of studying the fields of obesity, metabolism, and aging for the past 20 years and felt an increasing desire to share what I’ve learned with as many people as possible the past few years.

    More About Dr. Anton

    Real science. Real advice. Straight to your inbox!

    Get the latest news on topics like intermittent fasting, healthy aging, reducing obesity, and more.