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Intermittent Fasting for Strength Training: Benefits, Drawbacks, and Best Practices

Intermittent Fasting for Strength Training: Benefits, Drawbacks, and Best Practices

Intermittent fasting has become a popular approach to weight loss. From Kardashians to newspaper columnists, there have been plenty of high-profile fans of intermittent fasting in its various forms.

But what if you're trying to build the lean muscle that's so crucial to a long and healthy life? If your goal is to gain strength and build this muscle, could eating less frequently and consuming fewer calories hinder your progress?

Below, we'll look at what intermittent fasting really means, who it helps, and how meal timing can help you with your fitness goals.  

How and why is strength training crucial to health and longevity?

Call it what you want - strength training, resistance training, weightlifting - they all refer to exercises that involve working against a resistance, such as weights, resistance bands, or body weight. Even if you're not interested in building visible muscle, strength training is a crucial component of health and longevity.

Here are some reasons strength training is so important:

What does diet have to do with building muscle?

Of course, building muscle requires more than just doing planks or picking up weights. Your body needs the tools to turn that energy from exercise into matter (in this case, muscle).

When we consume food, our bodies break down the nutrients into energy and use it to fuel various physiological processes. One of these is called muscle protein synthesis, during which the body uses amino acids obtained from our food to create new proteins. These proteins are then used to create new muscle fibers.

In order for this process to work, we need a consistent source of calories from proteins, carbohydrates, and fat. But what if we're restricting our eating window to 8 hours a day? Can we still consume enough calories? And can we avoid our body's propensity to break down muscle tissue to use as fuel during fasting periods?

What is intermittent fasting?

Intermittent fasting (IF) involves cycling between periods of eating and fasting and typically involves restricting daily calorie intake for somewhere between 12 and 24 hours at a time. The goal is to let your body burn through the calories consumed during recent meals, get to the point of caloric deficit, and then begin to burn excess fat reserves. This is called metabolic switching.

Those who engage in intermittent fasting for physical health (as opposed to religious purposes) may or may not restrict the types of foods they eat during non-fasting hours. For example, some people choose to combine IF with a low-carbohydrate diet. However, for many people, the goal of a prolonged fast is to limit overall food intake so that they don't have to restrict the types of foods they eat during their eating windows.

Because there are so many ways to engage in intermittent fasting, it's challenging for researchers to gauge the overall benefits.

Types of intermittent fasts

There is some controversy over how to categorize intermittent fasting. But, in general, you will hear the following regimens referred to as intermittent fasts:

Time-restricted feeding (TRF)

This approach involves eating all meals within a specific window of time each day. For example, you might choose to eat all meals between 12 pm and 8 pm, and then fast for the remaining 16 hours.

The most popular TRF regimens are:

  • 16/8: Fasting for 16 hours per day and eating within an 8-hour window.
  • 14/10: Fasting for 14 hours per day and eating within a 10-hour window.
  • 12/12: Fasting for 12 hours per day and eating within a 12-hour window.
  • 20/4 Fasting for 20 hours per day and eating within a 4-hour window.
  • 23/1: Fasting for 23 hours per day and eating within a 1-hour window. (This often involves eating one large meal each day at the same time and can be referred to as OMAD, or "one meal a day.")

5:2 fasting

This is a periodic fasting approach that involves eating normally for five days a week and then severely restricting calories (usually to around 500-600 calories) for two non-consecutive days of the week.

Alternate-day fasting

There are two approaches to alternate-day fasting: complete and modified.

  • Modified fasting involves alternating between days of unrestricted eating and days of severe calorie restriction (usually around 500 calories per day).
  • Complete fasting typically requires participants to abstain from consuming anything but water (or at least eliminating any energy-containing food or drink).

Periodic fasting

This approach involves fasting for several days or longer on a periodic basis (such as once a week or once a month).

  • One type of periodic fasting is called prolonged fasting. This involves 2 to 21 days of energy restriction (typically water fasting).
  • Fast-mimicking diets (FMD) are another form of periodic fasting that involves consuming a low-calorie diet for a short period of time (such as 5 days) in order to mimic the effects of a water-only fast. While it's still unclear how effective FMDs really are, the goal is to achieve metabolic switching without depriving the body of the protein it needs to build muscle.

Some researchers distinguish periodic fasting from intermittent fasting.

Determining which specific fasting regimen is right for you and whether intermittent fasting is even conducive to your strength training goals will depend on your body's individual needs.

Assessing your nutritional needs may require working with a healthcare professional, especially if you suffer from a medical condition or are at risk of developing a chronic disease.

What are the pros and cons of intermittent fasting?

When you fast long enough that your body begins to use fat as fuel, it can not only increase fat burning and lead to weight loss, but it can also help improve your insulin sensitivity. In the long run, this can help reduce your risk of type 2 diabetes and other chronic diseases and may help improve body composition, so you build lean muscle and avoid accumulating excess body fat.

IF has also shown promise for protecting long-term cognitive function and reducing the risk of neurodegenerative diseases such as Alzheimer's. And there is also evidence (though still mostly in animal studies) that fasting can help reduce inflammation in the body.

Despite the benefits of intermittent fasting, it can potentially have drawbacks for those looking to optimize their muscle growth and strength gains.

Is intermittent fasting right for strength training and muscle building?

Whether intermittent fasting is right for strength training and muscle building depends on several factors, including your protein intake, meal timing, meal frequency, and your workout routine.

In order to build muscle, the body needs to be in a state of caloric surplus (consuming more calories than it burns) and have enough protein to support muscle growth. Individuals who engage in intermittent fasting may have difficulty consuming enough calories and protein to support muscle growth.

Ideally, you want to consume protein and carbohydrates at least two hours before and right after your workout to support muscle growth and recovery. If you are fasting during these periods, it may be more difficult to meet your nutritional needs and optimize your workout routine.


The type and frequency of exercise you engage in play the biggest role in muscle growth. Resistance training is key for stimulating muscle growth, so those who engage in intermittent fasting should ensure that they are engaging in these workouts regularly.

Benefits of intermittent fasting for strength training

Intermittent fasting may facilitate muscle building in the body by:

Improving insulin sensitivity

Insulin is a hormone that plays a key role in the transport of nutrients needed to build and maintain muscle tissue.

Increasing growth hormone production

Growth hormone aids in muscle recovery, helping to repair damaged muscle tissue and reduce inflammation.

Improving autophagy

Autophagy is a cellular repair process that can be activated by nutrient deprivation. It involves the breakdown and recycling of damaged or dysfunctional cells and helps support the generation of new cells that can aid in muscle growth.

Increasing protein synthesis

IF's ability to increase growth hormone production, improve nutrient partitioning, increase energy metabolism, and activate autophagy all help facilitate a process called protein synthesis. This is the process by which the body builds new proteins, including the proteins that make up muscle tissue.

Drawbacks of intermittent fasting for strength training

Intermittent fasting may also come with drawbacks for strength training. These may include:

Reduced energy availability

Calorie restriction can lead to reduced energy availability and make it harder to perform high-intensity strength training workouts that help build muscle.

Potential muscle loss

If your calorie deficit is too severe or protein intake is inadequate, it can lead to muscle loss and impede further strength training.

Reduced training intensity

Periods of fasting may deplete your energy and reduce your ability to achieve the training intensity necessary for muscle building during your workout routine.

Nutrient deficiencies

If you're not consuming enough food during eating periods or if your diet is not properly balanced, you can increase your risk of nutrient deficiencies. This can impair muscle growth and recovery and negatively impact overall health.

Best practices for making strength gains while intermittent fasting

If you are interested in engaging in practicing intermittent fasting while simultaneously trying to build muscle, it's vital to consider the following best practices:

Choose a sustainable IF protocol

Selecting an IF plan that is sustainable for your lifestyle, current health status, and fitness goals is crucial. Consult with a healthcare professional to ensure your plans don't pose a risk to your health.

Time your meals strategically

Time your meals to ensure that you have enough energy to support your workouts. This may involve consuming a pre-workout meal that is high in protein and carbohydrates as well as a post-workout meal that is high in protein to support muscle recovery and growth.

Prioritize protein

Adequate protein intake is critical for supporting muscle growth and repair. Research shows that between 0.7–1 gram of protein per pound of body weight is normally adequate to build strength when combined with resistance training. However, this also depends on your current body composition and fitness level.

Monitor energy levels

IF can lead to reduced energy, particularly if your calorie deficit is too severe or if nutrient intake is inadequate. It is important to monitor your energy levels and adjust your calorie intake or fasting schedule as needed to ensure that you have enough energy to support your workouts and daily activities.

Allow for adequate recovery time

Strength training involves breaking down muscle tissue, which requires time for repair and recovery. It is important to allow for adequate recovery time between workouts.

Get smart about strength training

When done correctly, intermittent fasting can support strength training and muscle growth.

And by utilizing the Speediance smart home gym, you can get the best insights into how your body is responding to your training. Speediance is able to track and monitor performance metrics such as heart rate, target muscle group, time under tension, lifted weight, and calories to give you the data and insights you need to make progress without overdoing it on days when you're restricting calories.

A holistic approach to fitness that incorporates intermittent fasting, a high-protein diet, strategic meal timing, cardiovascular exercise, and innovative technology may be just what you need to achieve your strength training goals and support your overall health and wellness.

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