Should I Be Using Different Fuelling Strategies When On My Period?

If you're a female triathlete who's ever questioned whether your nutrition needs to change depending on where you're at in your cycle, you're not alone.

Hormones shift throughout the month and can influence everything from metabolism and hydration to gut function and sleep. But does that mean you need a completely different fuelling plan when you’re on your period?

Let’s break down what the latest research actually says and what that means for you on the ground as a training triathlete.

The Four Phases of Your Cycle Explained

Before we dive into what to do, it helps to understand what’s happening.

1. Menstruation (Day 1–5): Oestrogen and progesterone are low.
   
2. Follicular Phase (Day 1–14): Oestrogen rises as your body preps for ovulation.
   
3. Ovulation (around Day 14): A spike in oestrogen, luteinising hormone and FSH.
4. Luteal Phase (Day 15–28): Both oestrogen and progesterone are elevated.

Cycle length can vary between 21 to 35 days and even differ month to month.

What Does the Research Say About Performance and Your Period?

Two key studies give us some helpful insights

1. McNulty et al. (2020)

• A large review of performance across menstrual cycle phases in naturally cycling women
  
• Found that performance was slightly lower during the early follicular phase (aka your period)
  
• But the difference was small, labelled "trivial", and not confidently different from zero
  
• Highlighted major limitations: low-quality studies, small sample sizes and inconsistent tracking methods
  
  

2. Schlie (2025)

• A more selective and robust study that used hormone verification (not just calendar tracking)
  
• Found that 58% of included studies showed some phase-related performance effects
  
• Again, early follicular phase showed some disadvantages for VO₂ max and peak power
  
• However, explosive strength and most other variables showed no change
  
  

Key Takeaways for Triathletes

So, should you overhaul your fuelling plan each month? Short answer: no.

Here’s what you need to know:

1. Any performance change is small.

There may be subtle drops in endurance or power during your period, but they're not significant enough to warrant a massive strategy change.

2. Everyone is different.

Some athletes feel invincible mid-cycle and sluggish during menstruation. Others feel no difference at all. Tracking your cycle alongside performance can reveal personal trends.

3. Don’t fall for generic advice.

Many social media "experts" overstate the impact of hormones on performance. We're just not at a point yet where firm, cycle-based training or fuelling guidelines can be recommended.

4. It’s okay to adapt.

If you feel low on energy, bloated or off your game during your period, you can make small tweaks:

• Prioritise iron-rich foods
  
• Keep up hydration to counter fluid shifts
  
• Focus on easily digestible carbs if gut function is off
  
• Be flexible with session intensity if needed
  
  

Real Athlete Talk

“I used to blame my period for every bad session,” says one age-group triathlete in our community. “Now that I track my cycle and understand my body better, I fuel smart and stop stressing.”

Personalised Over Prescriptive

The current evidence doesn’t support a blanket change in fuelling strategies across the cycle. What it does support is listening to your body, tracking what works for you and adapting as needed.

So rather than throwing out your plan every month, take a personalised approach. That’s where real performance gains are made.

What to Do Next

Want to make sure you’re not missing something crucial in your fuelling strategy? 

Grab the Triathlon Nutrition Checklist

Interested in learning more about hormones and training? Check out Do Female Athletes Need More Iron?

Reference

McNulty, K. L., Elliott-Sale, K. J., Dolan, E., Swinton, P. A., Ansdell, P., Goodall, S., Thomas, K., & Hicks, K. M. (2020). The effects of menstrual cycle phase on exercise performance in eumenorrheic women: A systematic review and meta-analysis. Sports Medicine, 50(10), 1813–1827. https://doi.org/10.1007/s40279-020-01319-3

Schlie, J., Krassowski, V., & Schmidt, A. (2025). Effects of menstrual cycle phases on athletic performance and related physiological outcomes: A systematic review of studies using high methodological standards. Journal of Applied Physiology. https://doi.org/10.1152/japplphysiol.00223.2025