Navigating the Hormonal Impacts of Intermittent Fasting for Women

Intermittent fasting (IF) is among the most common strategies for weight loss. It’s been shown to improve not just weight but also metabolic health, chronic inflammation, and aging. However, some reports suggest that the diet may be less effective for female patients.

According to Kaely McDevitt, RD, founder of KM Nutrition, few studies explore the impacts of IF on women specifically, a common theme throughout medical research. McDevitt, whose virtual private practice specializes in hormone balance and digestive health, said many of her clients have attempted IF only to worsen their hormone problems, particularly those of childbearing age.

"Anytime something is touted as a one-size-fits-all solution, we're going to run into problems because everyone is so different,” said McDevitt. “And we have people in very different seasons of life all trying to apply the same thing with different outcomes.”

While the research is limited, there is evidence suggesting that women may respond differently to IF compared to men. A 2005 study on the impacts of alternate-day fasting on insulin sensitivity found that IF was significantly less effective in women. Other studies have suggested that it could disrupt the balance of female hormones, specifically dehydroepiandrosterone (DHEA), a hormone that improves ovarian function and egg quality. 

The Effects of Fasting on Reproductive Hormones

According to Robert Silverman, DC, DACBN, DCBCN, MS, CCN, CNS, the reasons women respond differently to IF all come down to hormones. Studies have suggested that when fasting, females exhibit a heightened sympathetic nervous system activity—the fight or flight response—compared to males, leading to a more dramatic impact on their hormones.

“Fasting makes estrogen and progesterone nosedive,” said Dr. Silverman, founder and CEO of Westchester Integrative Health Center. "It affects gonadotropin-releasing (GnRH) hormones, making the body behave as if food is scarce, which effectively lowers estrogen and progesterone.”

Silverman explained that reduced progesterone levels can lead to PMS-like symptoms due to its role in mood stabilization. And decreased levels of estrogen, vital for various bodily functions, can affect numerous physiological processes, from hunger signaling in the brain to muscle recovery, Silverman added.

Engaging in intermittent fasting inappropriately can also lead to reduced thyroid function and irregular or absent periods, McDevitt said. The physiology of childbearing-age and menstruating females is centered around safety and energy availability so they can procreate or maintain a menstrual cycle. “So, anything we do from a dietary standpoint that either withholds feeding for a specific time or total input of calories has the ability to negatively impact hormones," she explained.

How to Approach Intermittent Fasting for Women

Despite concerns, many integrative practitioners like Kellie Blake, RDN, LD, IFNCP, who specializes in functional nutrition and co-owns NutriSense Nutrition Consulting, believe that the physical and mental benefits of IF outweigh the potential risks on female hormones, most of which appear to be minor. 

Research has shown that IF could have significant benefits for women with certain conditions. A study on women with polycystic ovary syndrome (PCOS) found that time-restricted eating had beneficial effects on weight loss, menstruation, insulin resistance, hyperandrogenemia, and chronic inflammation.

Additionally, post-menopausal women may respond more favorably to IF than those of childbearing age, according to McDevitt. “Hormones settle into just the low kind of flat rates once we go through menopause, and that's more conducive to intermittent fasting being effective and safe,” she said.

Many experts agree that, when used appropriately, IF can benefit women regardless of their age or condition. Dr. Silverman is a big proponent of IF, but he said it’s important to personalize the diet patient to patient, especially when trying to balance female hormones.

Before starting a female patient on IF, integrative practitioners may want to keep some tips in mind, such as:

• Consider stages of the menstrual cycle. According to Dr. Silverman, during the last seven to ten days of their cycle, when progesterone levels rise, it's advisable for women to shorten their fasting period to a maximum of 12 hours. This will help prevent a significant drop in progesterone, which can lead to PMS symptoms.
• Prioritize adequate protein intake. Due to the risk of inadequate protein intake during fasting, Blake emphasizes the importance of preserving muscle mass in aging women. She recommends a moderate overnight fasting period of 12 to 14 hours and a protein-rich meal of about 30 grams post-fast to optimize muscle protein synthesis.
• Focus on specific macronutrients for breakfast, lunch, and dinner: For optimal results, Dr. Silverman recommends starting the day with water in the first hour upon waking, followed by coffee in the second hour, along with a substantial breakfast focusing on proteins and fats while limiting carbohydrates to maintain autophagy. Then he suggests eating a lunch that has a balanced mix of carbohydrates, fats, and proteins, and a light dinner consisting of green vegetables and proteins.
• Suggest short-term intermittent fasting. While IF can be detrimental to reproductive hormones, it could be a helpful tool in the short term, said McDevitt. IF can help restore insulin sensitivity and healthy body composition, optimizing health for fertility.  
• Don’t push it. IF isn't for everyone, and no one should feel like they have to practice intermittent fasting, Blake said, especially if they're metabolically healthy and active. However, she encourages most of her clients to take a 12-hour rest from digestion overnight to optimize sleep and metabolic health. 

According to Dr. Silverman, there are certain patients should avoid IF, including some athletes and people with type 1 diabetes, certain sleep disorders, thyroid issues, high cortisol stress, and a history of eating disorders. In addition, he said women who are pregnant or breastfeeding, under 18 percent body fat, or are being treated for infertility should avoid the diet. 

Although the research is still limited and, just like any intervention, it should be used with caution, IF has definite applications for female patients, said McDevitt. “I think that there's still a way to marry these worlds of being cautious and respectful to hormones and not adding too much stress to the body while still benefiting from occasional fasting," said McDevitt. "It's just a risk-reward analysis for each client."

Every patient is different, Dr. Silverman added, and a cornerstone of integrative medicine is recognizing their individual needs and designing a care plan accordingly.

“There's obviously no superiority between the sexes, but there are differences,” said Dr. Silverman. “And one of the things that we all have to do as integrative practitioners is understand those differences and take them into account.”