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Should You Be Doing Fasted Workouts?

Should You Be Doing Fasted Workouts?

Endurance AthletesSports NutritionWellnessRunning

Fasted versus fueled training has become a popular topic as exercisers want to maximize their goals in both performance and body composition. Does training on an empty stomach lead to increased fat burning? What about the effects on performance? Here we navigate when fasted versus fueled training may be most appropriate.

Defining the Fasted State:

A true fasted state means that the body has been unfed (no calories at all) for at least 8 hours. This typically occurs naturally over the course of sleep. If following an intermittent fasting plan, typical plans advise a minimum of 12 hours unfed.

What Does the Research Say About Training In Fasted vs. Fed States?

In general, it has been shown that fasting is associated with weight loss, however both lean mass (muscle) and fat mass decrease as a result. Research has investigated the outcomes of fasted versus fed state training in relation to variables such as short term endurance performance, weight changes, and substrate utilization. Most research shows that fasted training may be okay for short duration (<60 min), submaximal training. Fasted training may limit performance or cause muscle breakdown if training at high intensities or long durations (>90 min).

This 2020 review concluded that performing endurance training while fasted increases fat oxidation due to increased adipose tissue lipolysis, increased plasma adrenaline and cortisol levels and lower insulin levels. However, this study found that changes in body composition were predominantly linked to a calorie deficit diet versus the presence or absence of fueling prior to training. Both studies found that training in the fasted state is associated with decreased physical performance. 

Another study shows that the downfall of fasted endurance training is the risk for protein degradation, or muscle breakdown. Training sessions lasting longer than 90 minutes without fuel is associated with increased amino acid (muscle) breakdown for fuel. Meaning that while weight loss may occur due to fasted training, it may be coming from muscle breakdown. Overall, studies show that more research is needed to identify the long term effects on fasted exercise. 

When Is Eating Before Training Highly Recommended?

Fueling prior to training is recommended for most athletes or individuals training at high levels and those seeking performance related outcomes. Fueling prior to training may be best or recommended if:

  • Your workout is longer than 60 minutes

  • You’re looking for physical performance results

  • You haven’t eaten in over 3 hours

  • You notice fatigue, hunger or decreased performance during training

When Is Fasted Training Okay?

There are situations where training in the fasted state is okay and likely won’t cause negative outcomes. Fasted training may be best or recommended if:

  • Your workout is less than 60 minutes

  • It is a low intensity workout

  • You suffer from Irritable Bowel Syndrome or GI discomfort from food while exercising

So, Should You Train In A Fasted State?

Based on the current research, my recommendation to athletes or individuals looking to perform is to fuel prior to exercise. While there are situations where fasted training may be okay, more times than not having a pre-training fueling routine is best suited to support high training volumes and performance goals. For general exercise, testing out how you feel when exercising fasted versus fueled is also a good idea to find out what works best for you.

Article by: Nicole Legler, RD, Eleat Nutrition Intern

Angie Asche

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