Intermittent Fasting Part 2- Fasting and Weight Training

Intermittent fasting has been suggested to benefit the body in a variety of ways, but when it comes to building muscle, is lifting weights while fasting something you should do? Well, it may depend on your goals.

If your main motivation for lifting weights is fat loss and body composition, intermittent fasting may help you get lean, as there is evidence that supports the concept that fasted exercise may promote fat loss. https://www.jstage.jst.go.jp/article/jpts/27/6/27_jpts-2015-098/_article

When your insulin levels are low (you’re in a fasted state), your body uses body fat stores as the primary source of energy. However, this could be at the cost of losing some muscle mass and compromising performance. Remember that glucose (sugar carbohydrates from food) plays a crucial role in the recovery process after a lifting session- it restores depleted glycogen in our muscle tissues that helps us get big and strong.

Contradictory to the above results, another study found that lifting weights in a fasted state actually uses more stored muscle energy (glycogen) than fat. https://www.jstage.jst.go.jp/article/jpts/27/6/27_jpts-2015-098/_article This means burning through stored fuel (glycogen) instead of fat, which could result in decreased performance and endurance.

A comprehensive article from The Fitness Tribe which analyzed a variety of studies found the following benefits of weight training while fasting:

1. Burn More Fat Faster

When you’re in a fasted state, though, and glucose is unavailable, your body begins to convert fat into energy.

Research from Northumbria University found people can burn up to 20% more body fat by exercising in the morning on an empty stomach, rather than exercising after breakfast.

2. Increase Muscle Growth

Studies show fasted weight training results in greater anabolic response to a post-workout meal when compared to fed training.

This means fasted training can help your body respond better to post-workout nutrition and begin building and restoring muscle quicker.

Another study found fasting increased growth hormones by 2,000% in men and 1,300% in women! Growth hormones work to protect lean muscle mass and restore metabolic balance.

3. Improve Peak Power And VO2 Max

Studies show that fasted training can improve peak power and VO2 max.

Translating that into weightlifting benefits, fasted weight training could help improve lifting output over the duration of a workout.

VO2 max is vital to endurance athletes, but it also has a place in the gym. In short, VO2 is essentially your body’s ability to use oxygen.

Regarding weight training, studies show that those who have a higher VO2 max burn more fat from exercise.

So it makes sense that fasted training can help you burn more fat by increasing your VO2 max.

4. Improved Insulin Sensitivity

The typical Western diet has most people consuming more calories than the body needs. 
Even those who are weight training often eat more calories than needed to grow muscle.

After doing this for an extended period, the body becomes more resistant to insulin (the hormone responsible for delivering nutrients where they need to go).

Regular fasted training causes your body to release insulin less often, making your body adapt and become more sensitive to the limited amounts of insulin.

This increase in insulin sensitivity makes it easier for your body to convert energy, burn fat, and increase blood flow.

https://thefitnesstribe.com/fasted-weight-training/

As you can see from above, the research that we do have on the impact of weight training while fasting is mixed and inconclusive. Some studies show that intermittent fasting may negatively impact performance and muscle mass, while others show no change and some even show positive outcomes.

The takeaway: lifting weights while fasting may not be the best strategy during heavy lifting sessions if your goal is to build muscle-you may see better results if you lift weights during the windows of time that you’re eating. While there isn’t much research on fasting and weight training, there is extensive research that has proven the benefit of adequate nutrition to help build muscle.

Experiment with lifting in a fasted state vs. a fed state and see what feels best for you. Schedule your fast based on your own personal schedule, as the time at which you train may impact your fasting. Track your performance, pay attention to how you feel and adjust accordingly!