Exercise physiology research shows women's bodies respond very differently to fasted training than men's — and the science on why is pretty clear. Cortisol is already at its daily peak first thing in the morning. That's normal — it's part of what wakes you up. But when you add hard training on top of an empty stomach, your body isn't able to hit real training intensity without over-stressing itself. And without enough fuel available, the brain reads that as a shortage — so it shifts into conservation mode. For women, this matters more than most people realize. Much of sports nutrition science was originally built around male physiology — mostly young male athletes — even though that's not most of the population. Fasted training increases reliance on free fatty acids, and in women, that added cortisol interacts with estrogen, progesterone, and testosterone. Over time, that can affect thyroid function, resting metabolic rate, and even menstrual regularity — and it tends to get more pronounced heading into perimenopause, when baseline cortisol is already elevated. That's the physiology behind why you might feel exhausted mid-workout, shaky, or ravenous by 2pm. The fix isn't complicated — a small mix of protein and carbs before training helps stabilize blood sugar and blunt that cortisol spike. Think a banana with a little peanut butter, half a bagel, or oatmeal with berries, 30 minutes out. This isn't about willpower or "toughing it out." It's about giving your body what it needs to perform, preserve muscle, and keep your hormones working with you instead of against you!