Should Athletes Train Fasted?
- Shrey Aggarwal
- Aug 3
- 5 min read
A badminton player we work with in Hyderabad trained fasted for eleven months because a coach told him it would teach his body to burn fat. It did. His fat oxidation went up, his bodyweight came down 4kg, and his smash speed fell off a cliff in the third game of every match. The mechanism worked exactly as advertised. The outcome he actually cared about got worse.
That gap between "the metabolism changed" and "the athlete got better" is the whole fasted training question.
Quick Overview
What fasted training does to your metabolism
Train after an overnight fast and you burn more fat during the session. This is settled. Pooled data across 27 trials shows a clear rise in fat oxidation during fasted aerobic exercise, with correspondingly lower glucose and insulin than the fed state (Vieira et al., British Journal of Nutrition, 2016).
Where athletes go wrong is reading that as "I will lose more fat." Fat burned during an hour of exercise is a small slice of what you oxidise over 24 hours, and the body adjusts the rest of the day to compensate. Twelve weeks of resistance training done fasted versus fed, with calories matched, produced no meaningful difference in fat-free mass, strength, or body composition (Vieira et al., IJSNEM, 2025). If you want to change your body composition, the daily energy balance decides it. The timing of your first meal doesn’t.
The case for training low
There is a real argument here, and it isn’t about fat loss. Starting a session with low muscle glycogen amplifies the cell signalling that drives mitochondrial adaptation. Reviewing the train-low literature, augmented signalling showed up in 73% of studies, gene expression in 75%, and increases in oxidative enzyme activity in 78% (Impey et al., Sports Medicine, 2018).
That reads like a slam dunk until you check whether it made anyone faster. Only 37% of the performance trials in that same review showed improvement. The other 63% showed no change. So the muscle is doing more interesting things at a molecular level, and the stopwatch mostly doesn’t notice.
Train-low still has a place. It’s a periodisation tool for a specific block of easy aerobic work, not a default way to live.
What it costs you in the session
Fed athletes perform better in longer efforts. A meta-analysis separating performance from metabolic outcomes found pre-exercise feeding improved performance in bouts beyond about an hour, while fasted exercise produced the superior metabolic profile (Aird et al., Scandinavian Journal of Medicine & Science in Sports, 2018). Short sessions were a wash.
This is the trade you’re making. Fasted, you get a better adaptive signal and a worse session. If the point of the session is quality (intervals, heavy lifting, sport-specific skill work under fatigue, anything where technique degrades when you’re empty), you’ve paid for a signal you didn’t need with output you did.
The badminton player’s problem was exactly this. Fasted easy jogging would have cost him nothing. Fasted court sessions cost him the part of his game that wins points.
Who should skip fasted training entirely?
Anyone already at risk of low energy availability. Fasted training is one of the more efficient ways to accumulate hours of hard work on very little fuel, and athletes drift into an energy deficit without noticing. In elite endurance athletes, 38% reported using fasted training, and bone injury incidence was 1.61 times higher in current users than in those who had never used it or had stopped (Raleigh et al., European Journal of Sport Science, 2024). That’s an association, not proof of cause, and injury risk is always multifactorial. It’s still not a number to wave away.
If you have low energy availability, no training tweak and no supplement fixes it. The only thing that resolves it is a structured increase in calories.
Fueletics also steers female athletes away from habitual fasted training, particularly around menstrual dysfunction or a history of it, where the added stress on an already stressed endocrine system isn’t a trade worth making. Same for adolescent athletes, who are growing and have no business restricting fuel around training. And anyone with a bone stress injury history.
How Fueletics uses it with athletes
Fasted work goes on easy aerobic sessions under 60 minutes, and only on some of them. Zone 2 in the morning, black coffee if you want it, water throughout. That’s the whole application.
Everything else gets fuelled. Quality sessions, long sessions, anything competitive, anything with a skill component. For a 6 AM start where a full meal isn’t realistic, a banana and a glass of milk, or a small bowl of poha, forty minutes before is enough to change how the session goes. Athletes report the session felt normal instead of grim, which is itself worth something across a training block.
After training, what matters is that you eat well and eat enough, not that you eat within some narrow window. The clock pressure people put on their post-session meal isn’t supported by the evidence, and it makes recovery feel like an exam.
The Fueletics Perspective on Fasted Training
Fasted training is a tool with a narrow application and a wide fan club. The physiology is real, and the performance benefit largely isn’t, which is a combination that tends to produce very confident advice built on very little.
If you’re an endurance athlete doing high-volume aerobic work and you’ve got your energy intake handled, putting a couple of easy sessions a week in a fasted state is reasonable. If you’re a team-sport or racquet athlete, a strength-athlete, an athlete managing energy availability, or someone chasing fat loss, it gives you nothing that a calorie deficit wouldn’t give you more safely.
The player, from the start of this piece, now eats before court sessions and trains fasted twice a week on his easy runs. His weight is back up 2 kgs. His smash speed in the third game is back.
Whether fasted training suits you depends on your sport, your training load, and your current energy availability, and those aren’t things to guess at. If you’re still unclear on how to choose, start with the Fueletics sports nutrition assessment and work from your own numbers instead of someone else’s rule.
Research References
1. Vieira AF, Costa RR, Macedo RCO, Coconcelli L, Kruel LFM. Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis. British Journal of Nutrition, 2016;116(7):1153–1164. doi.org/10.1017/S0007114516003160
2. Vieira AF, Blanco-Rambo E, Guimarães MB, et al. Impact of Overnight Fasted State Versus Fed State on Adaptations to Resistance Training: A Randomized Clinical Trial. International Journal of Sport Nutrition and Exercise Metabolism, 2025;35(4):291–302. doi.org/10.1123/ijsnem.2024-0215
3. Impey SG, Hearris MA, Hammond KM, et al. Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis. Sports Medicine, 2018;48(5):1031–1048. doi.org/10.1007/s40279-018-0867-7
4. Aird TP, Davies RW, Carson BP. Effects of fasted vs fed-state exercise on performance and post-exercise metabolism: A systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 2018;28(5):1476–1493. doi.org/10.1111/sms.13054
5. Raleigh C, Madigan S, Sinnott-O’Connor C, Sale C, Norton C, Carson BP. Prevalence of reducing carbohydrate intake and fasted training in elite endurance athletes and association with bone injury. European Journal of Sport Science, 2024;24(9):1341–1349. doi.org/10.1002/ejsc.12170
