Fast Like A Woman
Smarter Not Harder is the Best Approach
Fasting has become one of the most talked-about strategies for reducing inflammation, improving metabolism, and restoring energy. But for women, fasting isn’t as simple as skipping breakfast. It’s a hormone-driven, stress-sensitive process that must be tailored to our biology—not copied from male-based research.
Why Fasting Hits Women Differently
Most fasting research has been conducted on men or postmenopausal women. There is significant gaps in research of women as they age and the impacts of fasting upon them. As Dr. Mindy Pelz notes, “All fasts aren’t created equal.” Women’s hormones—particularly estrogen and progesterone—fluctuate throughout the month and profoundly influence metabolism, stress resilience, and fat utilization.
Dr. Stacy Sims, an exercise physiologist known for her work on female physiology, emphasizes that “Women are not small men.” She points out that the same fasting protocols that improve insulin sensitivity in men can raise cortisol and suppress thyroid function in women, especially those who train hard or are already under stress.
Both experts agree: fasting should enhance a woman’s resiliency, not deplete it.
Hormones, Energy, and Fasting Windows
Women’s hormonal cycles can be divided into four phases: follicular, ovulatory, luteal, and menstrual. Pelz teaches that these phases should guide how and when you fast:
Follicular phase (Days 1–10): Estrogen begins to rise, improving insulin sensitivity. This is an ideal time for short to moderate fasting windows (13–15 hours).
Ovulation (Days 11–15): Energy peaks. You may tolerate slightly longer fasts (14–16 hours), but don’t push extremes.
Luteal phase (Days 16–28): Progesterone increases appetite and fluid retention. This is the time to shorten or skip fasting, focusing instead on protein and mineral support. In fact the body typically burns 300-600 more calories/day in this period. So there’s a reason you often feel ravenous and experience massive cravings during this phase.
Menstrual phase: Your body is shedding the uterine lining; fasting can add unnecessary stress. Focus on nourishment and rest.
Sims adds that women training in a fasted state—especially high-intensity exercise—risk low energy availability, which can disrupt menstrual cycles, suppress metabolism, and impair recovery.
The idea days available for fasting women who still have a cycle are 15 days of the month. Whereas the luteal and menstrual phase women should prioritize good nutrition, rest, and minimal stress. Fasting acts as a stressor to the body, so introducing fasting windows during the latter half of your cycle may tax your body more than benefit it.
Ideally, your experiencing a 12 hour fasting window naturally between dinner (hopefully around 5:30-6:30 pm) and breakfast (6:30-7:00 am).
The Problem With “Fast Like a Man”
In male physiology, fasting often boosts growth hormone and enhances fat oxidation. But in women, prolonged fasting—especially under caloric restriction—can elevate cortisol, reduce thyroid hormone conversion (T4 → T3), and slow metabolis.
Women’s bodies are evolutionarily wired to protect fertility and resist starvation. That means too much fasting, too soon, can backfire—leading to fatigue, fluid retention, anxiety, or plateaus in weight loss.
The decades of “thin-at-all-costs” messaging that dominated the 1980s and 1990s did lasting damage to female metabolism and mental health. Restrictive eating, chronic calorie deficits, and obsessive cardio routines were normalized as discipline—when in reality they were early forms of disordered eating.
Studies show that chronic dieting during those eras led to long-term alterations in metabolism, hormonal imbalance, and disordered relationships with food that many women still carry today (Stice et al., 2017; Becker et al., 2020).
That legacy is one reason why many functional and integrative clinicians are cautious and skeptical about modern GLP-1 agonists. While these drugs (like semaglutide and tirzepatide) can reduce appetite and improve glucose control, their mechanism—blunting hunger cues and altering gut-brain communication—can mimic the same stress pathways that disordered eating once triggered.
For women, the concern is not just about the short-term weight loss, but the long-term hormonal cost: suppressed ovulation, loss of lean mass, slowed thyroid output, and potential interference with the body’s natural appetite and reproductive signaling (Mounsey et al., 2024).
In other words, the cultural pressure to shrink our bodies has simply evolved—from “fat-free everything” to “pharmaceutical fasting.” The physiological toll is similar. That’s why fasting, when practiced today, must prioritize metabolic resiliency, nourishment, and body literacy, not deprivation.
A Smarter Framework for Women
Drawing from both Pelz and Sims, here’s a female-centric fasting framework designed to balance metabolism, hormones, and performance:
1. Start with rhythm awareness
Track your cycle or energy patterns for 1–2 months before adding fasting. Apps like Clue or Natural Cycles can help you see when your body’s most resilient.
2. Begin with short windows
Start with 12–13 hours (for example, 8 pm to 9 am). Once you’re comfortable, extend to 14–15 hours on non-training days. Avoid aggressive 17- or 18-hour fasts unless supervised and advised by a clinician.
3. Sync with training
Heavy lifting or endurance sessions → shorter fast or eat beforehand.
Mobility or recovery days → moderate fast.
High stress weeks → no fasting focus, just stable nourishment.
4. Nourish during your eating window
Women need adequate protein (1.6–2.2 g/kg bodyweight) to maintain lean mass (Sims, 2023). Pair protein with colorful vegetables, quality fats, and strategic carbohydrates to support thyroid and adrenal function.
5. Monitor, don’t force
If fasting causes poor sleep, swelling, irritability, or low energy, shorten your fasting window or take a break. These are signs your body perceives fasting as stress, not healing.
Fasting Through Life Stages
Reproductive years: Cycle-synced fasting works best (Pelz, 2022).
Perimenopause: Hormone fluctuations can make long fasts difficult—Pelz recommends “intuitive fasting” and nutrient cycling.
Menopause: Some women tolerate longer fasts again, but Sims advises maintaining energy availability to protect muscle, bone, and cognitive function.
Fasting for Women in Menopause and Post-Menopause
Menopause represents a major metabolic transition. As estrogen declines, women often experience shifts in insulin sensitivity, cortisol regulation, and muscle mass, all of which change how the body responds to fasting. In the reproductive years, estrogen plays a protective metabolic role—supporting glucose control and fat oxidation. After menopause, that buffer weakens, making women more susceptible to blood-sugar instability and central fat gain (Lovejoy et al., 2008).
1. Why fasting changes after menopause
Dr. Mindy Pelz (2022) emphasizes that fasting can become a powerful ally during menopause if it’s used to enhance metabolic flexibility rather than restrict calories. With estrogen lower, the body relies more on mitochondrial efficiency to manage energy. Strategic fasting—short to moderate windows of 14–16 hours—can improve insulin sensitivity and cellular repair (autophagy) without depleting stress hormones.
However, Dr. Stacy Sims (2023) cautions that fasting in this phase must always be paired with adequate protein and resistance training to preserve lean mass. Because estrogen loss accelerates sarcopenia and bone density decline, extended fasting windows or low-protein diets can worsen frailty and reduce metabolic rate.
“Menopausal women need fuel to maintain muscle integrity and prevent the metabolic slowdown that fasting too aggressively can trigger.” — Sims (2023)
2. Ideal fasting structure for post-menopausal women
Start conservatively: 12–14 hour fasting windows, 3–4 days per week.
Prioritize morning movement: Light exercise (walking, stretching) in a fasted state can support fat oxidation, but refuel with protein afterward.
Avoid long fasts (>18 hours): Extended fasting raises cortisol and may increase visceral fat storage (Varady & Hellerstein, 2021).
Protein is essential: Aim for 1.6–2.0 g/kg body weight daily, evenly distributed across meals (Phillips et al., 2020).
Break the fast well: Include high-quality protein, healthy fats, and colorful produce to support mitochondrial and hormonal function.
3. When fasting helps most
Pelz (2022) notes that short, strategic fasts—like a weekly 24-hour reset or time-restricted eating (TRE)—can:
Improve blood sugar regulation.
Enhance brain-derived neurotrophic factor (BDNF) for cognitive health.
Support liver detoxification and mitochondrial turnover.
Reduce hot flashes and inflammatory symptoms for some women.
But once again, plan these strategically in your schedule, with low stress and no intensive exercise.
4. When fasting can be counterproductive
If post-menopausal women experience fatigue, anxiety, disrupted sleep, or loss of muscle tone, the fasting window should be shortened or paused. High cortisol levels or chronic under-eating can mimic adrenal fatigue, worsening symptoms often attributed to menopause itself (Gibson & Mitchell, 2020).
When to Skip Fasting
If you’re experiencing thyroid dysfunction, adrenal fatigue, chronic inflammation, MCAS-like symptoms, or significant water retention, fasting may temporarily worsen stress load. Focus instead on nervous system repair—sleep, protein, sauna/cold therapy, and micronutrient repletion—before reintroducing fasting.
Practical Takeaways
Match fasting to your physiology, not someone else’s.
Cycle your fasts the way your hormones cycle.
Fuel well, don’t fear carbs or calories.
Prioritize recovery—your metabolism depends on it.
Measure success by how you feel, not how long you fast.
References
Becker, C. B., Jilka, R. L., & Polivy, J. (2020). Diet culture, disordered eating, and women’s health: A review. Eating Behaviors, 37, 101387. https://doi.org/10.1016/j.eatbeh.2020.101387
Hawkins, M., Tonelli, J., Kishiyama, S., & Nair, K. S. (2018). Gender differences in the metabolic response to fasting and exercise. Journal of Clinical Endocrinology & Metabolism, 103(9), 3316–3325. https://doi.org/10.1210/jc.2018-00316
Mounsey, A. L., Stevens, J. B., & Probstfield, J. (2024). GLP-1 receptor agonists and reproductive health: Implications for women’s physiology. Journal of Women’s Health, 33(2), 115–123. https://doi.org/10.1089/jwh.2024.0001
Pelz, M. (2022). Fast like a girl: A woman’s guide to using the healing power of fasting to burn fat, boost energy, and balance hormones. Hay House.
Pelz, M. (2023, March 2). A beginner’s guide to fasting. DrMindyPelz.com. https://drmindypelz.com/a-beginners-guide-to-fasting/
Sims, S. (2023). Fasting for active women: What the science really says. DrStacySims.com. https://www.drstacysims.com/newsletters/articles/posts/fasting-for-active-women-risks
Sims, S. (2023). Mainstream menopause advice is misleading active women. DrStacySims.com. https://www.drstacysims.com/newsletters/articles/posts/Mainstream_Menopause_Advice_Misleading_Active_Women
Stice, E., Gau, J. M., Rohde, P., & Shaw, H. (2017). Risk factors that predict future onset of each DSM-5 eating disorder: Predictive specificity in high-risk adolescent females. Journal of Abnormal Psychology, 126(1), 38–51. https://doi.org/10.1037/abn0000219
Gibson, C. L., & Mitchell, E. S. (2020). Cortisol, sleep, and metabolic adaptation in postmenopausal women. Menopause, 27(9), 1054–1062. https://doi.org/10.1097/GME.0000000000001584
Lovejoy, J. C., Champagne, C. M., de Jonge, L., Xie, H., & Smith, S. R. (2008). Increased visceral fat and decreased energy expenditure during the menopausal transition. International Journal of Obesity, 32(6), 949–958. https://doi.org/10.1038/ijo.2008.25
Phillips, S. M., Chevalier, S., & Leidy, H. J. (2020). Protein “requirements” beyond the RDA: Implications for healthy aging. Applied Physiology, Nutrition, and Metabolism, 45(6), 565–573. https://doi.org/10.1139/apnm-2019-0549
Varady, K. A., & Hellerstein, M. K. (2021). Alternate-day fasting and time-restricted eating: Long-term effects in women. Obesity Reviews, 22(S1), e13241. https://doi.org/10.1111/obr.13241