Gary BreckaHuman Biologist & Longevity Innovator

Why Fasting Feels Harder at Certain Times of the Month

27 Feb 2026 · 1 min

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In this video, Gary Brecka explains that fasting effectiveness is heavily influenced by a woman's menstrual cycle. He emphasizes that fasting should support health, not cause harm, and that individual biology must be considered. Recent research shows insulin sensitivity peaks during the follicular phase (days 1‑14), making this period optimal for fasting because the body more readily uses fat for fuel. Conversely, during the luteal phase the body becomes more insulin‑resistant, making fasting feel harder and less effective. Ignoring these cycle‑dependent metabolic changes leads many women to struggle with fasting protocols.

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It's so important to understand that fasting isn't about powering through pain. It's supposed to be a way to improve health outcomes, not make them worse. Your biology and current health status determine whether fasting will help you or harm you. And ignoring these biological realities is why so many people struggle with fasting protocols. For women, even the timing of your menstrual cycle can make the difference between success and struggle during a fast. New research indicates that the action of insulin is influenced by cycle timing. So during your follicular phase through ovulation, which is roughly days one through day 14 of your cycle, your insulin sensitivity is naturally higher. This is considered the best window for fasting. Your body is primed to use fat for fuel more efficiently during this time. But during your luteal phase, everything changes. Your body becomes more insulin resistant. Fasting during this phase feels much harder because your biology is literally working against you.