Briefing Document: Fasted Training for Strength and Hypertrophy
This document reviews current research on the impact of fasted versus fed training on muscle growth, strength gains, and body composition. It aims to clarify common misconceptions and provide evidence-based recommendations.

Key Themes and Findings
Challenging Extreme Claims:
The research debunks both the "fasted training is the worst thing for gains" and the "magical effects for fat loss and muscle gain" narratives. The consensus is that fasted training is neither universally detrimental nor a secret weapon.
Short-Term Fasting (10-12 hours) vs. Fed Training:
Vieira et al. (2025) Study: This randomized clinical trial directly compared 12 weeks of resistance training after a 10-12 hour fast versus 1-2 hours post-carbohydrate meal.
Muscle Growth & Strength: Both groups "saw improvements in muscle thickness, 1RM strength (bench press and knee extension), and lower-body power." This suggests that for general resistance training, a moderate fast does not inherently hinder these outcomes.
Body Composition: "Interestingly, the fasted group even had a slightly greater increase in fat-free mass, although that was likely a result of them gaining more body weight throughout the intervention." This nuanced finding indicates that while fat-free mass increased, it might not be solely attributable to superior muscle gain in the fasted state.
Highly Restrictive Fasting (e.g., Ramadan) and Performance:
Triki et al. (2023, 2024) Study: This research examined the impact of training before or after breaking a "pretty 'hardcore' version of fasting" during Ramadan (abstinence from food and drink from dawn to sunset).
Body Composition: Both fasted and fed groups "lost body weight and fat during Ramadan, with their lean body mass remaining stable throughout the intervention." This highlights the potential for fat loss even with this restrictive fasting protocol.
Strength Gains: Significant differences emerged in strength:
During Ramadan, "squat and deadlift strength improved in the fed group only (by ~5kg and ~9kg, respectively)."
Post-Ramadan, "the fed group made greater strength gains in the deadlift and squat (~4kg and ~10kg more than the fasted group)."
Hormonal Response: Both groups experienced an increase in cortisol during Ramadan, returning to baseline afterwards. The fed group saw an increase in testosterone, though the source notes this is "unlikely to have made a big difference from a muscle growth perspective."
Key takeaway: The study underscores that "a highly restrictive form of fasting, where participants abstained from both water and food for several hours prior to training," can negatively impact strength performance.
Practical Recommendations and Nuances:
General Principle: "Overall, fasting is neither magic nor destructive for gains, especially if you train after breaking your fast."
Strength Athletes: "if you’re a strength athlete, it’s likely not a great idea to train completely fasted, as performance and, therefore, long-term strength gains may take a hit." This is crucial for individuals prioritising maximal strength development.
Limited Justification for Fasted Training: The author sees "no solid reasons to train fasted except for the once-in-a-blue-moon rushed training session... or for religious purposes, such as Ramadan."
Infrequent Fasted Training: "training completely fasted once in a while is unlikely to impact your long-term strength or hypertrophy gains significantly."
Personal Preference and Mitigating Performance Loss: "if you prefer training fasted and feel fine while doing so, it’s likely that you won’t be significantly sabotaging your gains, especially if you’re not particularly interested in 1RM strength."
Simple Pre-Workout Fueling: For those who prefer morning workouts and don't like to eat heavily, "having a piece of fruit or even a sugary drink, like a glass of orange juice, is an easy way to fuel early workouts." This strategy can "help avoid some of the potential performance drawbacks associated with training completely fasted without feeling like you’re actually eating."
Most Important Ideas/Facts
Fasted training (10-12 hours) does not appear to significantly hinder muscle growth, strength, or power in the short term, compared to fed training. The Vieira et al. (2025) study supports this.
Highly restrictive fasting (e.g., without water) does negatively impact strength performance and gains, especially for compound lifts. The Triki et al. (2023, 2024) studies provide clear evidence for this.
Strength athletes should generally avoid completely fasted training to maximise performance and long-term strength gains.
For the average individual, occasional fasted training is unlikely to cause significant long-term detriments.
Simple carbohydrate intake (e.g., fruit, juice) before an early morning workout can effectively mitigate performance issues associated with completely fasted training.
There is no strong scientific evidence to support "magical" benefits of fasted training for muscle gain or fat loss over fed training.