Gary BreckaHuman Biologist & Longevity Innovator

The Right Time for Women to Fast | Join the FREE 3-Day Water Fast Challenge

12 Oct 2025

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A brief guidance segment arguing that fasting should improve health and that biological factors—particularly a woman’s menstrual cycle phase—strongly influence fasting success. It states that insulin sensitivity is higher from the follicular phase through ovulation (roughly days 1–14), making that the optimal window for fasting, while the luteal phase is marked by relative insulin resistance and increased difficulty fasting.

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.