Intermittent fasting is a prolonged period without eating, often praised for its potential health benefits, including improved insulin regulation, weight management, enhanced cognitive function, and increased longevity. (1)
However, there’s an ongoing debate about intermittent fasting‘s impact on female athletes compared to male athletes. Some claim intermittent fasting may negatively affect women’s hormonal health.
Dr. Layne Norton addressed these concerns by analyzing the scientific evidence. Spoiler alert: they do not support the claims that intermittent fasting is bad for women.
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Intermittent Fasting: Who Is It Good For?
Numerous randomized human-controlled trials have shown that intermittent fasting effectively manages calorie intake. Randomized control trials are the gold standard in scientific research because they eliminate selection bias and provide more reliable results. These studies show various forms of intermittent fasting can aid in weight loss and improve metabolic health.
Intermittent fasting is not inherently superior to traditional calorie restriction — it’s another tool for managing diet. What sets intermittent fasting apart is its popularity and ease of adherence. Many find intermittent fasting allows for larger, more satisfying meals within a shorter eating window, enhancing feelings of satiety, which makes dieting more sustainable.
Does intermittent fasting disrupt women’s hormones? Dr. Norton says no, arguing that individuals seeking to sell “magic” solutions often promote this claim, preying on fears rather than facts.
Cortisol & Fuel Mobilization Response
Dr. Norton challenges the misconception that skipping breakfast elevates cortisol levels, explaining that cortisol naturally increases in the morning as part of the body’s mobilization of energy. Cortisol levels also increase during exercise. “Does that mean we shouldn’t exercise either?” Dr. Norton posed.
According to Dr. Norton, people often focus on temporary hormonal responses, like the rise in cortisol, without understanding their limited impact. Brief increases in hormones such as cortisol serve as part of the body’s fuel mobilization process and are vastly different from chronic cortisol elevation, which can lead to endocrine dysfunction.
The belief that fasting in the morning, combined with already elevated cortisol levels, disrupts female sex hormones lacks any scientific basis. (2)
“Low energy while intermittent fasting in the morning [is not] because of a small acute rise in cortisol. Using that logic, don’t exercise because exercise elevates cortisol,” Dr. Norton said.
Cortisol makes energy available to the body, which is important upon waking. After fasting overnight, the body needs to mobilize fuel to kick-start the day.
It’s important to distinguish between a short-term, acute rise in cortisol, designed to release energy efficiently, and prolonged, low-level hormone elevations. Chronic cortisol elevation can result from stress, obesity, or underlying endocrine disorders and may have adverse health implications. “Those are very, very different and should be treated as such,” Dr. Norton exclaimed.
Intermittent fasting can be an effective tool for women to manage their calorie intake if they choose to incorporate it. Dr. Norton asserts that standard intermittent fasting protocols, such as 16/8, 18/6, or 20/4, don’t affect hormonal health negatively. However, research is limited on extreme practices, such as prolonged multi-day fasting, so it remains unclear how they might affect hormones. “If you like [intermittent fasting] and it helps you stick to a diet, it’s perfectly reasonable,” Dr. Norton concluded.
References
- Patterson, R. E., Laughlin, G. A., LaCroix, A. Z., Hartman, S. J., Natarajan, L., Senger, C. M., Martínez, M. E., Villaseñor, A., Sears, D. D., Marinac, C. R., & Gallo, L. C. (2015). Intermittent Fasting and Human Metabolic Health. Journal of the Academy of Nutrition and Dietetics, 115(8), 1203–1212. https://doi.org/10.1016/j.jand.2015.02.018
- Cienfuegos, S., Corapi, S., Gabel, K., Ezpeleta, M., Kalam, F., Lin, S., Pavlou, V., & Varady, K. A. (2022). Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials. Nutrients, 14(11), 2343. https://doi.org/10.3390/nu14112343
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