Why Intermittent Fasting Doesn’t Always Work For Menstruating Women
Here’s what to do instead: break the fast before you break a sweat!
If you experience a natural cycle, you can implement periodized workouts and nutrition to leverage your innate metabolic flexibility. No fasting is required to regularly flip this switch.
Short on time? Here are the key takeaways:
The goal of intermittent fasting is to flip a metabolic switch that forces the body to use fat for fuel. Though favorable in the short term, the benefits of IF are not generally sustainable in menstruating and menopausal women.
If you experience a natural cycle, you can implement periodized workouts and nutrition to leverage your innate metabolic flexibility. No fasting is required to regularly flip this switch.
In menstruating women, repeated fasting can promote undesirable metabolic adaptations including fat storage, lower energy levels, and muscle breakdown. Not to mention chronic stress.
Repeated training in a fasted state can contribute to prolonged periods of elevated cortisol. This can produce inflammation and poor immunity, promote belly fat and decrease muscle, and leave you feeling burned out.
Intermittent Fasting and Fasted Training
As the intermittent fasting (IF) trend continues and busy schedules make it increasingly difficult to eat before and after exercise, this article aims to provide a clear argument for breaking the fast before you break a sweat along with a practical strategy for weight loss in each phase.
Let’s start with the theory behind fasted training and why it has become a go-to for fitness enthusiasts and those with weight loss goals.
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The guidance included in this post is intended for active women participating in some form of regular resistance training and exercise.
Information in this post and on this web site is provided for informational purposes only. The information is a result of practice experience and research by the author. This information is not intended as a substitute for the advice provided by your physician or other healthcare professional or any information contained on or in any product label or packaging. Do not use the information on this web site for diagnosing or treating a health problem or disease, or prescribing medication or other treatment. Information and statements regarding dietary supplements have not been evaluated by the Food and Drug Administration and are not intended to diagnose, treat, cure, or prevent any disease. Always speak with your physician or another healthcare professional before taking any medication or nutritional, herbal, or homeopathic supplement, or using any treatment for a health problem.
Improving Metabolic Flexibility
Without going into the metabolic complexities that occur during intermittent fasting, we can simplify the overarching goal of this method as follows: to flip a metabolic switch that promotes fat burning for energy. Intermittent fasting promises metabolic flexibility wherein the body is optimized for whatever fuel source is available at a given time. [1]
By extension, fasted training posits that if you exercise in a fasted state when glycogen (stored glucose) is already depleted, your body will rely on what’s available (fat) for fuel during workouts. In theory, if you burn fat during exercise, then you will lose weight.
There is growing research to support the long-term benefits of intermittent fasting for mice [10] and men [9]. However, for active women, there is a point at which the chronic stress of fasted training starts to take a toll and the benefits are not sustainable. [7] Female physiology is more complex and responds to fasting differently.
Takeaway → The goal of intermittent fasting is to flip a metabolic switch that forces the body to use fat for fuel. Though favorable in the short term, the benefits of IF are not generally sustainable in menstruating and menopausal women.
Menstruators Naturally Flip This Metabolic Switch
As mentioned above, one of the greatest benefits of IF is improved metabolic flexibility. Menstruating women however, are already predisposed to being metabolically flexible as a result of the hormone fluctuations—namely estrogen and progesterone—that occur throughout the menstrual cycle.
The switch to carbohydrate sparing and fatty acid utilization occurs naturally at various times each month when estrogen hormones are elevated. If we design exercise and nutrition programming to mirror the metabolic shifts that occur throughout the cycle, we can work with our physiology for better results and less stress—while staying empowered in our food choices before and after workouts!
In addition to being metabolically flexible, women’s brains are more sensitive to nutrient levels/demand and therefore have a lower threshold for disruptions.
With repeated fasting and unfueled workouts, estrogen levels take a hit and the endocrine system becomes dysregulated over time. This can lead to negative outcomes like muscle wasting, increased belly fat, and irritability.
Takeaway → If you experience a natural cycle, you can implement periodized workouts and nutrition to leverage your innate metabolic flexibility. No fasting is required to regularly flip this switch.
Sex Differences in Survival Strategy
In Dr. Stacy Sim’s ROAR [2], she describes the sex differences in our response to fasting. When calories are deficient, the shared signal received is “famine.” How the body interprets that signal is very different for a man compared to a woman.
Male or female, the body will always choose survival over reproduction. The key sex difference is how our physiology adapts to improve our survival odds—optimizing performance in men and efficiency in women.
In a food-scarce environment, men lean out and preserve muscle to build a fight-ready frame. If food is limited and survival depends on a man’s ability to chase down his next meal or fight for limited resources, his chances are significantly improved by optimizing his physiology for performance.
Female physiology on the other hand, approaches survival differently. A woman’s body preserves resources and downregulates reproductive function because it would be ill advised to create more mouths to feed when food is limited. With repeated fasting, female sex hormones are inhibited, fat stores accumulate, and cortisol runs wild.
Takeaway → In menstruating women, repeated fasting can promote undesirable metabolic adaptations including fat storage, lower energy levels, and muscle breakdown. Not to mention chronic stress.
The Stress Response
Finally, let’s touch on the stress hormone cortisol as it relates to fasted training. This hormone serves myriad functions—it helps regulate blood sugar and metabolism, stabilizes blood pressure, and governs sleep cycles.
Cortisol responds to positive and negative stressors alike by bringing survival systems online and curbing those it deems nonessential—digestion, immune function, and reproduction to name a few. It also makes substances like glucose and amino acids more available to meet immediate needs.
Our cortisol-fueled stress response however, was not intended for long-term use.
As hormone expert Nicole Jardim clarifies, it was designed to prioritize performance over all other metabolic functions to give us a quick hit of energy and address a real-time threat. [5] A threat that was quickly neutralized and followed by a period of rest and recovery.
Cortisol and Exercise
During a workout, cortisol spikes in response to the exercise stimulus and this brief surge leads to better performance, improved memory, and higher pain threshold. When this response is fueled by food and followed by an immediate recovery period, exercise-induced cortisol has a net positive effect. It functions very much as intended by catalyzing a brief state change that neutralizes an external stimulus.
On the flip side, when we produce a high energy demand in a fasted state, compounding stress signals can lead to prolonged periods of elevated cortisol. [8]
When combined with modern lifestyle stressors like work and relationships, chronically high cortisol can increase inflammation, impede immune function, and promote muscle breakdown. It can also lead to excess belly fat in women in an effort to protect vital organs. [6]
Influence on Sex Hormones
Through the lens of hormone health, Jardim refers to cortisol as a queen hormone because of its influence over the rest of the endocrine system.
For example, cortisol dampens release of ovulation-triggering hormones which can disrupt the natural rise and fall of estrogen and progesterone. [4] This queen also blocks progesterone receptors which can worsen PMS and has been shown to impact egg maturation in the follicular phase. [3]
Takeaway → Repeated training in a fasted state can contribute to prolonged periods of elevated cortisol. This can produce inflammation and poor immunity, promote belly fat and decrease muscle, and leave you feeling burned out.
As you continue exploring cycle syncing as a strategy for weight loss, muscle gain, and your other fitness goals, you might be wondering what a periodized approach to intermittent fasting looks like. In the next blog post, I’m sharing what you can do instead of intermittent fasting as a menstruating woman to keep your hormones happy and avoid the potential downside of running on empty. Let’s dive in →
de Cabo, R., & Mattson, M. P. (2019). Effects of Intermittent Fasting on Health, Aging, and Disease. The New England journal of medicine, 381(26), 2541–2551. https://doi.org/10.1056/NEJMra1905136
Sims, Stacy T. ROAR: How to Match Your Food and Fitness to Your Female Physiology for Optimum Performance, Great Health, and a Strong, Lean Body for Life. Rodale. 2a. The Betty Rocker Show (Host), (2021), Season 2 Episode 3 “Eating and Training with Your Cycle Part 1 With Dr. Stacy Sims, https://thebettyrocker.com/eating-and-training-with-your-cycle-part-1-with-dr-stacy-sims/
Jimena, P., Castilla, J. A., Peran, F., Ramirez, J. P., Vergara, F., Jr, Molina, R., Vergara, F., & Herruzo, A. (1992). Adrenal hormones in human follicular fluid. Acta endocrinologica, 127(5), 403–406. https://doi.org/10.1530/acta.0.1270403
Michael, A. E., Pester, L. A., Curtis, P., Shaw, R. W., Edwards, C. R., & Cooke, B. A. (1993). Direct inhibition of ovarian steroidogenesis by cortisol and the modulatory role of 11 beta-hydroxysteroid dehydrogenase. Clinical endocrinology, 38(6), 641–644. https://doi.org/10.1111/j.1365-2265.1993.tb02147.x
Jardim, Nicole. (2022) How Stress Affects Your Menstrual Cycle. Fix Your Period. https://nicolejardim.com/how-stress-affects-your-menstrual-cycle/
Moyer, A. E., Rodin, J., Grilo, C. M., Cummings, N., Larson, L. M., & Rebuffé-Scrive, M. (1994). Stress-induced cortisol response and fat distribution in women. Obesity research, 2(3), 255–262. https://doi.org/10.1002/j.1550-8528.1994.tb00055.x
Hackett D, Hagstrom AD. Effect of Overnight Fasted Exercise on Weight Loss and Body Composition: A Systematic Review and Meta-Analysis. Journal of Functional Morphology and Kinesiology. 2017; 2(4):43. https://doi.org/10.3390/jfmk2040043
Hackett D, Hagstrom AD. Effect of Overnight Fasted Exercise on Weight Loss and Body Composition: A Systematic Review and Meta-Analysis. Journal of Functional Morphology and Kinesiology. 2017; 2(4):43. https://doi.org/10.3390/jfmk2040043
Elizabeth F. Sutton, Robbie Beyl, Kate S. Early, William T. Cefalu, Eric Ravussin, Courtney M. Peterson, Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes, Cell Metabolism, Volume 27, Issue 6, 2018, Pages 1212-1221.e3, ISSN 1550-4131, https://doi.org/10.1016/j.cmet.2018.04.010
Mitchell, S. J., Bernier, M., Mattison, J. A., Aon, M. A., Kaiser, T. A., Anson, R. M., Ikeno, Y., Anderson, R. M., Ingram, D. K., & de Cabo, R. (2019). Daily Fasting Improves Health and Survival in Male Mice Independent of Diet Composition and Calories. Cell metabolism, 29(1), 221–228.e3. https://doi.org/10.1016/j.cmet.2018.08.011
Geiker, N. R., Ritz, C., Pedersen, S. D., Larsen, T. M., Hill, J. O., & Astrup, A. (2016). A weight-loss program adapted to the menstrual cycle increases weight loss in healthy, overweight, premenopausal women: a 6-mo randomized controlled trial. The American journal of clinical nutrition, 104(1), 15–20. https://doi.org/10.3945/ajcn.115.126565
Draper, C.F., Duisters, K., Weger, B. et al. Menstrual cycle rhythmicity: metabolic patterns in healthy women. Sci Rep 8, 14568 (2018). https://doi.org/10.1038/s41598-018-32647-0
