Feel Like You Should Train Fasted? Here’s Why You Shouldn’t.
You’ve probably heard the hype about how fasted training supposedly has some performance benefits. The idea that you can wake up in the morning and just head straight to your workout without having to take the time to eat seems really convenient, right? A lot of athletes are drawn to the idea of fasted training too because they believe it will help them adapt to use fat as a fuel source, that it can also improve their performance, or they worry about getting sick to their stomach if they eat right before a workout. All of these reasons seem pretty valid and even beneficial.
Is fasted training worth the hype?
As science and training theories have evolved we’ve gained a lot of insights on what the actual impact of fasted training is, and it’s not as magical as it seems.
While it may sound nice to be more adapted to using fat as a fuel source, the research says there is little evidence to backup the idea that fasting even helps our bodies adapt to using fat as a fuel source. Even if fasting did make the body able to use fat as a fuel source more readily, this would only maybe be beneficial for ultra-endurance athletes who are exercising for extremely long amounts of time and want to be able to eat and get energy from multiple sources (including carbs!) - all to avoid flavor fatigue and take in enough energy from food. Even in this case, these athletes still want to be taking in carbs as their main fuel source!
As far as performance goes, multiple research articles have shown that intermittent fasting doesn’t increase performance; if anything, it impairs performance.
You can still find some research out there that says fasted training has benefits for athletes, but it's important to remember that the vast majority of the current research (and also research that’s been done over the past 40-50 years) points towards carb intake and fueling our bodies sufficiently being the best thing we can do not only for our performance but for long term health outcomes.
How fasted training will affect your body
One thing that is SO important to point out is that most of the research that has been done on intermittent fasting showing benefits are done in groups of people who live sedentary lifestyles and were metabolically unhealthy - aka NOT athletes. They found that in these groups there were reductions in fasting glucose, appetites, and insulin sensitivity. Intermittent fasting in these groups triggered cardio metabolic changes, but guess what? Those changes also happen with chronic endurance/aerobic exercise.
And exercise offers even more benefits! Exercise also improves muscle mass and bone mineral density, but fasting as an athlete can is very risky because it decreases your energy availability since you’re eating less. This can cause low bone density, cardiovascular dysfunction, GI issues, and loss of menstruation (for females) and libido, along with many other long term health issues. One study even found that the incidence of bone injury was 1.61 times higher in those who currently do fasted training compared to athletes who never tried fasted training. Reducing your 24 hour intake in any form easily leads to a state of low energy availability - and if an endurance athlete doesn’t get out of that state of low energy availability, combined with other risk factors, it will cause poor bone health.
Even if you feel fine exercising in the mornings before you’ve eaten anything or during the day if you haven’t eaten for a while, there are other things happening in your body that aren’t fine.
You have to remember that just because one nutrition strategy works for someone does not mean that it works for everyone. Someone that struggles with seizures may benefit from the keto diet, but if you don’t have seizures then it probably won’t be beneficial. Someone who has Celiac disease shouldn’t eat gluten, but if you don’t have Celiac then you don’t need to cut gluten out of your life. Being an athlete means that you’re going to require more food to sustain everything that your body is doing, so just like someone with seizures or Celiac adjusts to take care of their body, you should do the same!
What the majority of top athletes are doing
Maybe you don’t care about this, but it’s helpful to checkout what the pros are doing to see what actually works! You may find one or two professionals who swear by fasted training or low carb diets, but when we look at the vast majority of professionals and those who are consistently at the top of leaderboard we see a different story:
Paige Onweller - won the 104.2-mile Big Sugar Gravel Pro Women's title and always takes in around 120 grams of carbs per hour
Dan Green - Broke the 2025 Cocodona 250 course record and ate 115 grams carbs per hour
Emily Harrop - Won the Crystal Globe for the 2023-2024 season and eats 60-90 grams of carbs per hour (for longer and shorter events)
Cam Wurf - Broke the 2025 Ironman Bike Split world record (going 28.7mph for 112 miles) and was eating 200+ grams of carb per hour
You may not be a professional athlete, but if the professionals are choosing to fuel and being so successful — it really shows that fueling has major benefits!
Pre-workout snack ideas that are easy on your stomach
If you’re worried about your stomach being queasy eating right before a workout, then gut training is for you! Start off with just a little bit, something tolerable, and work your way up.
Here are some quick easy snacks that are a little easier to stomach so you can eat before a workout to make sure you’re fueling your body adequately:
Bananas, rice cakes, pop tarts, applesauce, fig bars, juice, gummies, and sports drinks.
Once a light snack, around15-30g of simple carbs, settles well you can add a little more until you work up to having a solid snack of 30-60g of carbs before your workout! Not only will you see the benefits in your performance, but you’ll feel better.
And always remember, a fueled body performs better than a fasted body.
References:
Rothschild, J. A., Kilding, A. E., & Plews, D. J. (2020). Prevalence and determinants of fasted training in endurance athletes: a survey analysis. International journal of sport nutrition and exercise metabolism, 30(5), 345-356.
Zouhal, H., Saeidi, A., Salhi, A., Li, H., Essop, M. F., Laher, I., ... & Ben Abderrahman, A. (2020). Exercise training and fasting: current insights. Open access journal of sports medicine, 1-28.
Burke, L. M., Ross, M. L., Garvican‐Lewis, L. A., Welvaert, M., Heikura, I. A., Forbes, S. G., ... & Hawley, J. A. (2017). Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. The Journal of physiology, 595(9), 2785-2807.
Kanter, M. (2018). High-quality carbohydrates and physical performance: expert panel report. Nutrition today, 53(1), 35-39.
Amawi, A., AlKasasbeh, W., Jaradat, M., Almasri, A., Alobaidi, S., Hammad, A. A., ... & Ghazzawi, H. (2024). Athletes’ nutritional demands: a narrative review of nutritional requirements. Frontiers in Nutrition, 10, 1331854.
Mountjoy, M., Ackerman, K. E., Bailey, D. M., Burke, L. M., Constantini, N., Hackney, A. C., ... & Erdener, U. (2023). 2023 International Olympic Committee’s (IOC) consensus statement on relative energy deficiency in sport (REDs). British journal of sports medicine, 57(17), 1073-1098.
Parr, E. B., Devlin, B. L., Radford, B. E., & Hawley, J. A. (2020). A delayed morning and earlier evening time-restricted feeding protocol for improving glycemic control and dietary adherence in men with overweight/obesity: a randomized controlled trial. Nutrients, 12(2), 505.
Logue, D. M., Madigan, S. M., Melin, A., Delahunt, E., Heinen, M., Donnell, S. J. M., & Corish, C. A. (2020). Low energy availability in athletes 2020: an updated narrative review of prevalence, risk, within-day energy balance, knowledge, and impact on sports performance. Nutrients, 12(3), 835.
Raleigh, C., Madigan, S., Sinnott‐O’Connor, C., Sale, C., Norton, C., & Carson, B. P. (2024). Prevalence of reducing carbohydrate intake and fasted training in elite endurance athletes and association with bone injury. European Journal of Sport Science, 24(9), 1341-1349.
Martinez, I. G., Mika, A. S., Biesiekierski, J. R., & Costa, R. J. (2023). The effect of gut-training and feeding-challenge on markers of gastrointestinal status in response to endurance exercise: A systematic literature review. Sports Medicine, 53(6), 1175-1200.
