Dr. Mindy Pelz opens Fast Like a Girl with her foundational critique: popular intermittent fasting protocols were largely developed and initially tested predominantly on male research subjects, producing guidance that Pelz argues poorly fits women's genuinely distinct hormonal cycling patterns, potentially producing suboptimal or even counterproductive results when applied without this gender-specific adaptation.

Pelz's foundational argument:

• She argues that women's menstrual cycles involve significant, regularly recurring hormonal fluctuations that meaningfully affect metabolic response to fasting, meaning a single, unvarying fasting protocol applied consistently regardless of cycle phase fails to account for this genuine physiological variation
• Pelz draws on her functional medicine clinical practice, describing patient patterns where standard, male-oriented fasting protocols produced disappointing or even counterproductive results for female patients, motivating her development of this cycle-adapted alternative approach
• This foundational critique sets up the book's overall project: presenting a specific fasting protocol explicitly adapted to different phases of the female menstrual cycle, along with specific guidance for women in perimenopause and menopause whose hormonal patterns differ further from both the standard male-oriented protocols and from a regularly cycling premenopausal pattern

This foundational framing establishes Pelz's distinctive approach: applying intermittent fasting's broader popularity and research base specifically through this female-physiology-adapted lens, rather than treating fasting protocols as gender-neutral without this specific hormonal consideration.