Fasted Vs. Fed Exercise: I Tried Both And Here Are The Results

Most people who want to lose weight want to lose it fast. And recently, fasted exercise, or working out on an empty stomach, is being touted as the golden ticket. The idea is that exercising in a fasted state will help you shed more weight faster because you’re directly utilizing fat stores, as opposed to last night's dinner, for energy. But do you really have to fast before your sweat sesh for it to be more effective? The short answer: No.

The Effects of Fasted Exercise on Weight Loss and Body Composition

A 2017 systematic review and meta-analysis of 5 studies published in the Journal of Functional Morphology and Kinesiology found no correlation between training in a fasted state and greater weight loss. The studies included a total of 96 adult participants who were split into two groups: (1) participants who exercised after an overnight fast and (2) participants who exercised in a fed state, after consuming a standardized meal and then measured in terms of body mass and/or body composition. The results? The effects of fasted exercise versus fed exercise on weight loss were found to be trivial. The study also found that fasted exercise had little to no positive (or negative) effects on body composition, or the amount of fat and muscle in the participants. In other words, fasted exercise isn't the end-all-be-all to fat loss, either.

The Pros and Cons

Food blogger and fitness fanatic Amanda Meixner of MeowMeix says there are pros and cons to both fasted and fed exercise.

"I know many people who notice a boost in stamina during their workouts if they eat before. On the flip side, if you’re doing intermittent fasting or keto, not eating before your morning workout might be ideal for you.

Think about it: if you eat before your workout and notice you perform better, you’re more likely to burn more calories and get a greater benefit from your workout.

On the other hand, if eating before your workout makes you feel sick mid-sprint and you feel just as strong skipping the AM meal, then that’s a total win!"

Go With Your Gut (Literally)

I lost 20 pounds last year without working out fasted. I was training to compete in my first bodybuilding show, which involved lifting moderate-to-heavy weights on top of 45-60 minutes of cardio 6x a week. Since my training schedule was already pretty rigorous and my intake was low, the handful of times I tried working out fasted just resulted in me feeling depleted and hungry. This isn’t to say fasted exercise is bad or that you can’t lose those extra 5, 10, 20 pounds doing fasted workouts; you most certainly can. This is just to say you should listen to your body and do what’s right for you and your goals. Fasted exercise isn’t necessary for weight loss. But if your schedule only allows you to work out in the mornings and you’re just not hungry, or you get nauseous whenever you eat before exercising, then by all means, go fasted. But you don't need to do fasted exercise, and shouldn't, especially if you don’t like it or feel like you’re starving yourself. According to nutritionist Keri Glassman: "Depending on how long and intense your workouts are, you may find your performance suffers if you don’t fuel beforehand. If you’re running 12 miles to train for a race, for example, or lifting heavy weights, your body will likely need the fuel to keep you moving."

The Bottom Line

Weight loss shouldn’t be a quick fix. Fitness needs to be sustainable for long-term health, and you'll only achieve lasting results if you actually enjoy the journey. If you want to do fasted exercise, cool. And if you don’t, that’s cool, too. Fasted or fed, as long as you’re mindful of your calories and sustaining a caloric deficit over a period of time, you're well on your way to hitting that weight loss goal.   Original images of the author, Sarah Carter, taken by Tina Leu Fotos.  

READ THIS NEXT

Nutritionist Keri Glassman explains how food works to fuel exercise and gives her take on fasted cardio. Plus, here’s what to do if you hit a weight loss plateau.

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