To Feed or Fast?

By Coach Mel

As an early-morning athlete, I’ve always trained in a fasted state—meaning I regularly hit my workout after fasting for 8–10 hours overnight. For a long time, I assumed this meant higher fat oxidation (aka, burning more fat). Social media certainly backed me up on that one 😉.

At the same time, as a female athlete, I also saw plenty of posts warning that fasted training could wreak havoc on hormones. Conflicting messages everywhere.

So… what does the actual research say?

What the Research Shows

A recent study examined 12 weeks of fed-state vs fasted-state resistance training and looked at changes in:

• Body composition
• Muscle thickness
• Strength
• Power

The takeaway? Both approaches produced very similar results.

Here are the key findings:

• Fed and fasted resistance training led to similar gains in muscle size, strength, and power over ~12 weeks.
• The fasted group showed a slightly larger increase in fat-free mass, but the difference was tiny—not something you’d notice or rely on for an edge.
• Participants trained 2–3 sets of five exercises, twice per week, while maintaining a specific calorie goal. Not exactly CrossFit—but consistency matters.
• Pre-workout nutrition may matter more if you’re doing longer, higher-volume, or higher-intensity sessions, or if you’re in a significant calorie deficit.
• This study did not address sport-specific needs or elite athletes.

What This Means for Us

For the everyday CrossFit athlete, here’s the practical lens:

• If you like training fasted because it fits your schedule or you simply feel better, you’re not sacrificing hypertrophy, strength, or power.
• If your volume is high, you’re pushing long METCONs, you’re in a calorie deficit, concerned about hormonal health, or you just don’t like training hungry—training fed is also a great option.
• The study found no meaningful sex-based differences in response to fasted training. In this context, fasted training isn’t inherently riskier—or more beneficial—for women compared to men.

Common Social Media Concerns (And a Reality Check)

“Cortisol is the stress hormone.”
Yes, cortisol increases with fasting and hard training—but short-term increases are normal and not inherently bad. The issue is chronic, unmanaged stress, not temporary spikes from a fasted workout.

Reproductive hormones & energy availability
Most of the scary headlines come from situations involving low energy availability—not from well-planned fasted sessions paired with adequate daily calories. When overall fueling is sufficient, fasted training hasn’t been shown to disrupt menstrual health or hormonal function in healthy individuals.

Long-term health & low energy availability
Problems arise when athletes consistently chase extreme calorie deficits or combine high volume and high intensity without adequate fueling and recovery. That’s the issue—not an occasional 12–16 hour fast.

Bottom Line

• Protein matters. Aim for ~1.2–1.6 g/kg/day to support performance and hypertrophy, regardless of when you train.
• Track and adjust. Pay attention to how you feel, your performance numbers, and—if applicable—your menstrual cycle. If something feels off after a few weeks, change the approach.
• Meal timing matters far less than total energy balance over time.

If you’d like to dive into the research yourself, you can find the study linked here.

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Thanks for reading—and happy WOD-ing, fed or fasted 💪

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Coach Mel

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