Episode 283: Does Fasting affect your menstrual cycle?
The Truth About Fasting for Women: Why Most Studies Don’t Apply to Your Cycle
Balancing Hormones Naturally Podcast with Leah Brueggemann
Everyone keeps telling you to fast. Skip breakfast. Push your eating window. Drink coffee until noon. And somewhere along the way, fasting got marketed as the secret to weight loss, balanced blood sugar, and longevity for every human on the planet.
Here is what nobody mentions in those reels: most of the research behind those claims was done on men or postmenopausal women. If you have an active cycle, applying that data to your body without context can quietly tank your hormones, flatten your energy, and wreck your periods.
In this episode, Leah breaks down what fasting actually does to a cycling woman’s body, when it works in your favor, when it backfires, and the one fasting style most women can use safely without sending their adrenals into a tailspin.
What You’ll Learn in This Episode
• Why fasting research done on men doesn’t translate cleanly to menstruating women
• How estrogen and progesterone change your insulin sensitivity across your cycle
• The connection between aggressive fasting, LH pulsatility, ovulation, and progesterone
• Why intermittent fasting can become a fancy way of chronically under-eating
• What circadian fasting is, why Leah loves it, and how to do it
• Follicular fasting: the one-day-per-cycle window where a longer fast may serve you
• How melatonin and your circadian insulin sensitivity should shape when you eat
• Why your minerals and vital reserve matter before you ever consider a fast
• How to break a fast without spiking your blood sugar into the stratosphere
Key Concepts From the Episode
You’re Not a Small Man
Men run on a 24-hour hormonal rhythm. Women run on a 28 to 36-day rhythm. Their dominant hormone is testosterone, which doesn’t tank under stress the way progesterone does. Stretching male fasting protocols across a cycling woman’s body ignores all of that.
Insulin Sensitivity Changes Throughout Your Cycle
Estrogen increases insulin sensitivity. Progesterone decreases it. So depending on where a woman is in her cycle, the same fasting protocol can produce wildly different results. One snapshot in a study cannot capture that.
Aggressive Fasting Can Suppress Ovulation
Calorie restriction taken too far has been shown to lower LH pulsatility within just five days. Lower LH means a weaker ovulatory surge, which means a weaker corpus luteum, which means less progesterone. That cascade shows up as irregular cycles, thinning hair, irritability, low energy, and insomnia long before it shows up on a lab.
Sometimes Intermittent Fasting Is Just Under-Eating in Disguise
Slapping a name on a tiny eating window doesn’t change the math. If the calories aren’t there, the body reads starvation. The early energy boost most women feel? Usually adrenaline. Eventually the bill comes due in the form of stalled fat loss, blunted thyroid function, and worsening cycles.
Circadian Fasting: The Safer Default
Stop eating after dinner and don’t eat again until morning. Roughly a 12-hour window. This honors your natural insulin rhythm (you are more insulin sensitive in the morning, more resistant at night) and supports digestion and blood sugar without spiking cortisol. Most cycling women can use this safely.
Follicular Fasting (One Day Per Cycle)
Pick one day in your follicular phase and pull your final meal earlier (say, 3 pm instead of 6 pm). Estrogen is rising, insulin sensitivity is on your side, and the impact on stress hormones is minimal. One day. Then back to your normal circadian fast.
Mineral Status and Vital Reserve Come First
Fasting on top of depleted minerals and a chronically dieted body is pouring gas on a fire. Replenish first. Mineral-rich foods (yes, including beef liver, not only vegetables) build the foundation that any fasting strategy needs.
Practical Takeaways
• Eat within 30 to 60 minutes of waking
• Aim for 30 grams of protein at breakfast
• Get fiber and low-glycemic carbs in early
• Never eat a naked carb (pair the apple with a hard-boiled egg or a handful of nuts)
• Build a dinner that can actually carry you through the night: protein, fat, fiber, low-glycemic carbs
• Break your fast with protein, not sugar and coffee
• Prioritize nourishment before restriction every single time
• Pay attention to mineral intake, especially if you’ve been chronically dieting
A Line Worth Saving
“You don’t need to starve to heal. You need to support your hormones, not suppress them.”
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Want to Go Deeper?
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Connect With Leah
• Instagram (personal): @leahbru
• Instagram (podcast): @balancinghormonesnaturally
• Free Hormone Training: freehormonetraining.com
Disclaimer: This episode is for educational purposes and is not medical advice. Please work with a qualified practitioner before making changes to your nutrition, fasting practice, or supplement routine.
The recommendations presented in this podcast are not a substitute for medical advice from a qualified doctor. Before making any changes to your diet and lifestyle, please consult with your healthcare provider.
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