What the Science Really Says
You may have seen posts warning that fasted training is bad for women — that it spikes cortisol, disrupts hormones, and leads to belly fat gain. But what does the research actually say?
Let’s separate the myths from the science.
🥣 What the Guidelines Say
The American College of Sports Medicine (ACSM) recommends eating 1–4 g of carbohydrates per kilogram of body weight in the 1–4 hours before exercise lasting longer than an hour. This is designed to support performance — particularly during intense or prolonged sessions.
However, this isn’t a rule that everyone has to follow. The right approach depends on your goals, energy needs, and training type. Some athletes, for example, deliberately train fasted to help the body use fat more efficiently for fuel.
🧬 Where the “Hormone Chaos” Myth Comes From
A lot of scary claims about fasted training and women’s hormones come from animal research — particularly mouse studies where animals were severely calorie-restricted for long periods.
That’s a very different scenario from a healthy woman doing a morning workout without breakfast! These studies often show energy deprivation, not a simple fasted session. So, while interesting, they don’t translate to everyday training or nutrition for active women.
⚖️ What About Kisspeptin and Cortisol?
Kisspeptin is a hormone in the brain that helps regulate reproductive hormones. Some animal studies suggest fasting can lower kisspeptin levels and impact fertility — but again, this happens under extreme energy restriction, not in well-nourished women training fasted.
Cortisol, the body’s stress hormone, naturally rises during exercise. Fasted training can raise it a little more, but this is a normal physiological response — not something that causes belly fat or hormonal dysfunction.
The real concern isn’t fasted training — it’s low energy availability. When women consistently eat too little to support training and recovery, this can disrupt hormones, menstrual cycles, and overall health.
⚡ When to Train Fed vs Fasted
There’s no one-size-fits-all approach, but these guidelines can help:
Performance goal? Eat before. If your focus is intensity, speed, or strength, carbs help you perform your best.
Fat-adaptation or convenience? Fasted sessions can work fine for easy or moderate workouts, especially early in the day.
Multiple daily sessions? Fuel up. Eating before each helps recovery and prevents low energy availability.
Feeling tired, irritable, or losing your cycle? Avoid fasted training until energy balance is restored.
Both methods can be effective — it’s about matching your nutrition to your goals and recovery needs.
💬 Book a personalised consultation to learn how to fuel smarter for your training goals.
Check the information for yourself
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