It's one of the most persistent debates in the gym: should you lift on an empty stomach to maximize fat burning, or do you need to eat beforehand to fuel performance and muscle growth?
Everyone seems to have a strong opinion, but the evidence has been murky. Now, a new 2025 systematic review and meta-analysis by Vieira and colleagues has pooled the existing research to give us the highest level of evidence yet. The results are intriguing, but they come with a massive asterisk that you can't afford to ignore.
Let's break down what they found and what it means for your training.
A quick note: The full text of this study was not available, so this analysis is based on the abstract only.
What The Researchers Did
The goal of this study was to combine the results from all relevant clinical trials comparing resistance training in a fasted state versus a fed state. By pooling the data, a meta-analysis can give us a clearer picture than any single study could.
The researchers looked at four key outcomes in adults:
- Fat-Free Mass: Changes in muscle, bone, and water—basically, everything that isn't fat.
- Body Fat Mass: Changes in the amount of body fat.
- Muscle Hypertrophy: The technical term for muscle growth.
- Strength: Increases in maximal strength.
The Verdict on Muscle Growth and Strength
Let's get straight to the big question for most lifters: does training fasted kill your gains?
According to this analysis, the answer is no. The researchers found no significant differences between the fasted and fed groups for:
- Fat-Free Mass (p = 0.436)
- Muscle Hypertrophy (p = 0.366)
- Strength (p = 0.318)
This suggests that, based on the available evidence, training after an overnight fast doesn't seem to help or hurt your ability to build muscle and get stronger compared to training after a meal. This is great news for those who prefer training early in the morning or simply don't like the feeling of lifting with food in their stomach. Your gains are likely safe either way.
The Surprising Finding on Fat Loss
Here’s where things get interesting. While muscle and strength outcomes were similar, the same wasn't true for body fat.
The meta-analysis found that the fasted state was associated with greater reductions in body fat mass (p = 0.043). This was a statistically significant finding, suggesting that performing resistance training on an empty stomach might provide a slight edge specifically for fat loss.
This is the kind of headline that can send lifters flocking to fasted training. But before you ditch your pre-workout meal, you need to read the fine print.
The Critical Caveat: Why You Shouldn't Overhaul Your Routine Yet
This is the most important part of the entire study. While the fat loss finding is notable, the evidence it's built on is shaky, at best.
The researchers point out two major limitations:
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Only Four Studies Were Included: The entire conclusion of this meta-analysis is based on just four individual studies. In the world of research, this is a very small pool of data, making it difficult to draw firm, generalizable conclusions.
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High Risk of Bias: This is the real red flag. Of the four studies included, three were assessed as having a high risk of bias. In simple terms, this means there were likely flaws in the original study designs that could have skewed the results. When the majority of the evidence has a high risk of bias, we have to be extremely skeptical of the findings.
So, while the data points toward a benefit for fat loss, the data itself is weak. It's a signal, not a verdict.
Practical Takeaways for Your Training
So, what should you do with this information?
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For Muscle & Strength: The evidence is clear that it likely doesn't matter. The best approach is the one that allows you to train your hardest, consistently. If you feel weak and lethargic training fasted, eat something. If you feel sluggish and bloated after eating, give yourself more time to digest or train in a fasted state. Personal preference and performance should be your guide.
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For Fat Loss: The potential benefit of fasted lifting for fat loss is interesting but built on a weak foundation of evidence. Remember that the primary drivers of fat loss are your total daily calorie deficit, protein intake, and overall training volume. Chasing a small, uncertain advantage from fasted training at the expense of workout quality is a bad trade. If training fasted causes your performance to drop, you're likely doing more harm than good to your body composition goals.
The bottom line: This 2025 meta-analysis doesn't provide a compelling reason to change what's already working for you. It reinforces that for muscle and strength, personal preference rules. And for fat loss, it offers a tentative clue that needs to be confirmed by more, higher-quality research before we can treat it as fact.
Focus on the big rocks: train hard, eat right, and get enough sleep. Whether you do it with or without a pre-workout meal seems to be a minor detail in the grand scheme of things.
Reference:
Vieira, A. F., Blanco-Rambo, E., Macedo, R. C. O., & Cadore, E. L. (2025). Resistance training performed in the fasted state compared to the fed state on body composition and strength in adults: A systematic review with meta-analysis. Journal of bodywork and movement therapies. https://pubmed.ncbi.nlm.nih.gov/41316673/