Millions of athletes and fitness enthusiasts in the Muslim world face a practical question every year: what happens to my performance if I train while fasting? The question extends beyond Ramadan too, given how popular intermittent fasting and time-restricted eating have become among fitness enthusiasts generally. The answer research provides isn’t a simple “good” or “bad” — it’s genuinely nuanced. A systematic review and meta-analysis published in Sports Medicine in 2020 found that Ramadan fasting slightly reduces anaerobic (explosive) power, while showing no meaningful effect on aerobic endurance, muscular strength, or vertical jump height. This article unpacks what we actually know, and separates the effect of “food restriction” from the effect of the sleep disruption and circadian shifts that accompany Ramadan specifically.
What Did the Sports Medicine Review Find?
The review pooled studies measuring athlete and active-individual performance before and during Ramadan. The key findings: anaerobic power was negatively affected — average and peak power declined in Wingate and repeated-sprint tests during fasting. Morning sprint performance specifically declined, likely because the body has gone many hours without food or water since the pre-dawn meal. Aerobic endurance showed no significant effect in most studies. Muscular strength, jump height, fatigue index, and total work output barely changed. In short: very short, maximal-intensity efforts (seconds of repeated peak force) are most vulnerable to decline, while longer moderate efforts and single-rep strength hold up well.
Intermittent Fasting Outside Ramadan: A Calmer Picture
When intermittent fasting or time-restricted eating (like an 8-hour eating window with 16 hours fasting) is studied without Ramadan’s water restriction and sleep disruption, results are more neutral. A 2020 systematic review in Nutrients found that time-restricted eating was sometimes associated with improved VO2 max, while Ramadan fasting tended to lower it — a difference likely driven by dehydration and sleep disruption rather than fasting itself. A more recent 2025 meta-analysis concluded that intermittent fasting had no significant effect on blood lactate concentration, vertical jump height, handgrip strength, peak Wingate power, maximum bench press weight, maximum heart rate, or rate of perceived exertion.
Intermittent Fasting, Body Composition, and Resistance Training
One of the most studied applications: combining time-restricted eating with resistance training in trained individuals. Multi-week trials found this combination can reduce fat mass while preserving muscle mass and peak strength — genuine fat loss without meaningful muscle loss, provided adequate protein and appropriate training volume are maintained. This makes intermittent fasting a reasonable tool for fat-loss goals, not for maximal explosive performance. But its advantage in this context isn’t “magic” — studies matching calories and protein between a fasting protocol and a spread-out eating pattern found comparable body composition results. For many people, intermittent fasting’s real benefit is purely practical: fewer meals makes calorie tracking easier and adherence simpler, which alone may explain its success for those it suits.
Why Does Anaerobic Performance Suffer More Than Aerobic?
Short, intense anaerobic effort relies on stored muscle glycogen and adequate water and electrolytes for efficient neuromuscular signaling. After long fasting hours — especially without water, as in Ramadan — this availability drops slightly, affecting the ability to generate repeated maximal force. Moderate aerobic effort, by contrast, relies more on fat oxidation, and the body’s fat reserves are abundant and unaffected by a single day’s fast. Single-rep strength is a momentary effort that doesn’t deplete a reserve, so it stays relatively stable. This explains the pattern studies have observed.
There’s another factor tied specifically to water. Ramadan fasting is “dry” — no drinking during daylight hours — unlike most intermittent fasting patterns, which allow water. Even a mild 1-2% body water deficit reduces the ability to perform high-intensity effort, raises perceived exertion, and affects concentration and motor coordination. This explains why Ramadan fasting’s effect on performance is sometimes slightly worse than time-restricted eating in lab settings, even though the underlying principle — abstaining from food for hours — is the same. This is also why good hydration during the night hours — spread across the evening, not consumed all at once — is one of the most important things protecting performance during Ramadan.
What Happens in the Body During a Fasting Day?
In the hours after the pre-dawn meal, the body relies on glycogen stored in the liver and muscles to fuel the brain and muscles. As hours pass and liver glycogen depletes (roughly within 12-16 hours), reliance shifts toward fat oxidation and ketone body production as alternative fuel. This metabolic shift is normal and safe for most healthy people, and explains why aerobic endurance — which runs primarily on fat — stays stable. But muscle glycogen isn’t fully depleted during an ordinary fasting day without exercise, so fuel for short efforts remains partially available; the problem appears when intense exercise is added at the end of a long day, where reduced glycogen meets dehydration and the reduced alertness that comes from insufficient sleep.
Fasting and Muscle Building: What Do We Know?
A common worry is that fasting “eats muscle.” Evidence doesn’t support this concern under normal conditions. The body efficiently protects muscle protein during short fasts by shifting to fat as fuel. Trials of time-restricted eating combined with resistance training show preservation of lean mass and strength, provided three conditions are met: adequate daily protein (roughly 1.6 grams per kilogram of body weight), appropriate resistance training volume, and sufficient sleep. During Ramadan, this practically means distributing protein between the sunset and pre-dawn meals, not skipping resistance sessions, and avoiding the severe caloric deficit that combines little eating with heavy training.
Does the Response Differ Between Men and Women?
Most fasting-and-performance studies have been conducted on male athletes — a genuine gap in the literature. Some research suggests women’s response to extended fasting may differ due to hormonal and metabolic differences, and that some women are more sensitive to low energy availability, a condition linked to menstrual cycle disruption and bone health issues in female athletes. Extra caution is therefore warranted: monitoring total energy intake, avoiding combining fasting with severe caloric restriction and high training volume, and consulting a specialist for any menstrual changes or persistent decline in performance or mood.
Ramadan Specifically: It’s Not Just the Fasting
It’s important not to conflate Ramadan’s various changes. What shifts isn’t just abstaining from food and drink during daylight — it’s also shorter, fragmented sleep, meal timing shifting to nighttime, changes in meal composition (sometimes more sugar and fat), reduced daytime activity, and sometimes dehydration. Much of the performance decline observed during Ramadan is attributable to poor sleep and circadian disruption more than caloric restriction itself. This is genuinely good news practically: because most of these factors are manageable. Someone who regulates their sleep, maintains hydration, times training near the sunset meal, and maintains balanced nutrition may notice little difference in performance. Someone who neglects these factors — stays up late, drinks little, trains at noon after a long day, and eats heavy unbalanced meals at night — will feel a clear decline and mistakenly attribute it to fasting itself. Individual experience is the real judge here: track your performance, sleep, and energy during the first week and adjust based on what you observe, not general rules.
Practical Takeaways
- Expect only a slight decline in repeated explosive power: aerobic endurance and single-rep strength hold up well.
- Train near the sunset meal: this minimizes the impact of dehydration and low energy availability.
- Treat sleep as a training priority, not an afterthought: losing it is what actually undermines performance during Ramadan.
- Treat the month as a maintenance phase, not a record-chasing phase.
- For intermittent fasting outside Ramadan: it’s a reasonable tool for fat loss while preserving muscle, not necessarily better or worse than other eating patterns for performance.
- Consult a specialist if you have diabetes or take medications affected by meal timing, before any fasting regimen.
- Monitor your individual response for a week before judging; differences between people are large, and adjustment should be based on your own observation.
The bottom line: the relationship between fasting and athletic performance is nuanced, not absolute — short anaerobic capacity is somewhat affected, while endurance and strength remain largely stable. With good sleep, hydration, and timing management, most people can train and compete while fasting without meaningful loss.
It’s also worth remembering that Ramadan isn’t only a training month — it carries spiritual and social dimensions that may matter more than a number on a Wingate test. Many professional Muslim athletes have fasted while achieving major accomplishments, confirming that fasting and high performance aren’t contradictory. The goal of understanding this research isn’t to excuse inactivity or force peak performance on an exhausted body, but to make informed decisions that protect both fitness and health during the month, then resume progress afterward with a rested body.
Sources
- Effects of Ramadan Fasting on Physical Performance: A Systematic Review with Meta-analysis — Sports Medicine (2020)
- Effects of Intermittent Fasting on Specific Exercise Performance Outcomes: A Systematic Review Including Meta-Analysis — Nutrients (2020)
- Effect of Intermittent Fasting on Physical Performance and Exercise Outcomes: A Systematic Review and Meta-Analysis of Clinical Trials — Journal of Food Biochemistry (2025)
The information in this article is for educational purposes only and does not substitute professional medical or sports nutrition advice, especially for people with diabetes or those taking chronic medications.
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