Working Out on An Empty Stomach: Yay or Nay?

Working out on an empty stomach: yay or nay?

As a trainer, one of the top questions I get asked by my clients is if they should eat prior to working out. If your morning routine includes an early workout sesh, the idea of eating a full breakfast can be daunting. Over the years, you may have even trained yourself to not feel hungry in the morning—but that doesn’t mean you shouldn’t eat. And when it comes to exercise, there’s not much good that can come out of working out on an empty stomach. 

While every person is different and requires different types of fuel, I always encourage my clients to eat before hitting the gym or clicking ‘play’ on their favorite obé class. But wait, isn’t ‘fasted cardio’ a thing? And aren’t you supposed to ‘burn more fat’ doing a workout before your first meal?

Not quite. Here, I’ll break down why fueling up before a workout is so important—and explain the potential risks of working out on an empty stomach. Trust me, having a bite to eat before your movement session, even if it’s small, is well worth it. 

Working Out on an Empty Stomach: A Quick Biology Lesson

Before we get to the nitty gritty, let’s review some human biology. Your body relies on stored forms of carbohydrates, known as glycogen, for energy supply during exercise. As you exercise, your body breaks down that glycogen to maintain your blood glucose levels. When your glycogen stores are depleted, your body will turn to fatty acids for fuel. But that’s not necessarily a good thing. 

While some people believe exercising in a fasted state will encourage ‘fat burning’ (also known as fat oxidation), scientific evidence supporting this notion is hit or miss. A recent study that did suggest low-to-moderate intensity exercise (read: not high intensity!) can expedite fat oxidation was focused on trained males between the ages of 20 and 30—hardly a good representation for the general population. Plus, reaching this ‘fat burning’ state becomes less likely as workout intensity increases and is not recommended. 

A meta-analysis zeroing in on fasted cardio specifically found it had very little effect on body mass and body fat. Other studies failed to find weight-loss advantages associated with fasting—and if they did, the experiments were tightly controlled with help from nutrition scientists. A study on women, however, found no significant differences in body composition changes between those who fasted vs. ate before working out. 

Certain types of cardio (especially the hard stuff, like HIIT) paired with an empty stomach can actually lead the body to start breaking down muscle, not fat stores, for energy. That’s the last thing you want—since muscle mass is critical to good health. In other terms, your glycogen stores are essential for a safe and effective workout!

The TL;Dr is that your body needs fuel (think: protein and complex carbs) to make each workout work. Exercising in a fasted state (especially if it’s a pattern) can leave you feeling sluggish and low energy while stifling or regressing your fitness progress. Your body will always perform and recover better if you’re fed—especially for longer, higher-intensity workouts.

The Side Effects of Running on Empty

Working out on an empty stomach can also lead to both short and long-term health repercussions. In the short-term, some people experience nausea, fatigue, and discomfort while working out on an empty stomach. You may get edgy or have energy crashes later in the day, sturggle to get motivated, or find your mood to be unstable. Plus, a recent study found that exercise performance on an empty stomach was significantly reduced

If you’re planning on a short, low-intensity workout (say, a 20-minute Yoga class) skipping a pre-workout meal may not affect your training too much (just don’t make it a habit). However, if you’re planning on working out for longer than 30 minutes at a higher intensity, you’re likely to lose steam more quickly without some fuel beforehand. Not only that, but you also won’t reap as many benefits from your workout. Imagine a car that’s low on gasoline—it’s just not smart to rev the engine to 100 mph when you’re running on fumes. The same goes for your body! You’re less likely to exercise at your maximum capacity if you didn’t fuel up beforehand. 

In the long-term, not working out on an empty stomach can significantly affect your body’s ability to recover. Studies have shown that working out with depleted glycogen stores means your body will have less glycogen available to carry you through a recovery period. This is especially true if you’re tapping into protein reserves (aka burning muscle) to get through your session. Instead of recovering quickly and being able to stick to your routine, your body will need a lot more time to restore muscle and tissue function, making it harder to show up and feel good. 

Recovery aside, fueling up before your workout will also ensure you’re not ravenous after. While repressed recovery is certainly enough to convince many people to eat before their workouts, avoiding feeling hangry during the day certainly seals the deal. 

When (and What) Should I Eat Before a Workout?

I’m glad you asked! Typically, it’s recommended to eat a meal within 90 minutes to an hour before your workout. However, if you’re looking to get your workout in first thing in the morning, a small snack 30 minutes before will suffice. Aim for a carb-rich snack to help maintain blood sugar levels and keep glycogen stores readily available. 

Need some light snack or meal ideas? Here are a few things I love:

If you have to work out in the morning but don’t feel good after trying a light snack before, try to keep your morning sessions short and low-intensity. Try modalities like Yoga, Pilates, Barre, Yoga Sculpt, Sculpt, Walk, or Ride—and aim to not exceed 30 minutes. You can always do more later in the day! 

Real talk: We work out to improve muscle function and feel our best. If you’re working out consistently on an empty stomach, odds are that you’re going to feel more irritable, fatigued, and tired post-workout. If you aren’t reaping the benefits of your workout in the first place, it’s unlikely that you’re going to feel motivated to show up for yourself consistently. So, if you’re new to fueling up before a workout, try it—and see how you feel. It’s likely you’ll be able to lift heavier weights, run faster, and maybe even hit a new PR. Thank us later!

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  • Kat Brunner

    Kat is an obé Dance, Sculpt, Jump, and Bounce instructor with NASM CPT certification. She is also a professional health coach, certified by The Institute for Integrative Nutrition, an MS Nutrition Student at American University, and a passionate self-love advocate!

One response to “Working Out on An Empty Stomach: Yay or Nay?”

  1. Thank you so much for good nutritional info. Love that you are utilizing Kat’s wealth of knowledge.

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