Costs and Benefits of Fasted Training

No training fast? costs and benefits.

By Coach Lindsay Zemba Leigh


Athletes sometimes ask me about fasted workouts, and I continue to see articles about it in running and triathlon magazines. So, it will be helpful to offer our thoughts on the topic.

What are fasted/glycogen depleted workouts? Typically done in the morning after having a long night time fast, the athlete does their workout without eating anything beforehand, and not taking in any calories during the workout. Why? Some evidence suggests fasted workouts can promote fat oxidation, at least in young, healthy men (1).

However, here at No Limits, we do not promote doing fasted or glycogen depleted workouts because we feel the costs outweigh the benefits.

Depriving your body of calories during workouts will impede recovery, put you at greater risk of getting sick since your immune system can be suppressed, and you may not be as strong during the workout to hit the training targets, especially if you’re doing any high intensity or longer workouts. And after the workout, your metabolism may slow down due to your semi-fasted state.

Fasted workouts have been shown to be even more detrimental for women, having greater post-exercise immune stress and post-exercise inflammation compared to men (2). Women also show an increase in muscle tissue damage and breakdown and an increase in the stress hormone, cortisol (2). And in a study involving all female athletes, there were no changes found in body composition between fasted and non-fasted exercise when caloric intake was controlled (3).

When you are training hard, it’s easy to end up in a negative calorie balance since it’s hard to replace all calories burned in workouts, especially if you’re doing two workouts per day. Why put even more stress on your body by not fueling before and during workouts?

If you don’t have time to eat and digest before a workout, or don’t have an appetite first thing in the morning, have some easily digestible carbs like a glass of juice, a banana, a granola bar, or a piece of toast.

After your workout, you can eat the rest of your breakfast, including protein and some fruit or veggies or other healthy carbs.

Fuel your training and recover well – fasted workouts are not worth the risk.

Sims, S. 2016. Roar: How to Match Your Food and Fitness to Your Unique Female Physiology for Optimum Performance, Great Health, and a Strong, Lean Body for Life.

Costs and Benefits of Fasted Training
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