Does Fasting Wreak Havoc on Your Hormones?

Fasting has increased in popularity over the last decade for its many health benefits. There are several fasting methods to choose from, including intermittent fasting and time-restricted feeding, both of which involve alternating fasting and eating windows.

While specific timelines vary, I recommend a 12-15 hour overnight fast, which would give you a 9-12-hour daily eating window.¹ This promotes metabolic changes that lead to enhanced fat burning, improved insulin sensitivity, and hormone optimization.²

Despite the documented benefits of fasting, there’s a common concern among women: that fasting can wreak havoc on your hormones. While it's true that fasting involves changes in hormone levels, these alterations are typically part of the body's natural response to fasting. In other words, for most women, they’re short-lived, and any hormone elevations will adjust in time.

As you'll see, fasting doesn't mean your hormones are taking a permanent nose-dive!

Why Does Fasting Get a Bad Rap for Hormone Health?

Fasting often gets a bad rap for hormone health, particularly among aging women. As estrogen, progesterone, and testosterone levels decline during perimenopause and menopause, concerns arise about fasting's potential to worsen these hormonal shifts. Women worry that not eating for extended periods could mess with their metabolism, potentially spiking stress hormones or throwing reproductive hormones off balance.

However, current research, while not definitive, hints at fasting's capacity to reduce several menopausal symptoms by improving blood-sugar control, reducing high blood pressure, aiding in weight management, and lowering cholesterol levels. Fasting has also been shown to boost metabolism and lower inflammation, benefits that indirectly support hormone balance and help ease menopause symptoms.^3-5

Benefits of Intermittent Fasting

Research shows fasting has numerous benefits for middle-aged and older women. Beyond its metabolic effects, fasting may improve mood disorders, help you manage stress, and protect against certain cancers.^{6, 7}

Additional benefits include:

Weight loss: Restricting your food intake to a certain time period can help you lose weight and maintain a healthy weight. One review of 27 studies found people who did intermittent fasting lost up to 13% of their initial weight.⁸
Heart health: Intermittent fasting can reduce the risk of cardiovascular disease by helping you manage your weight, normalize blood pressure, support healthy lipid (fat) levels, and reduce your risk of diabetes.⁹
Hormone balance and menopause symptoms: Fasting can support hormone balance and alleviate menopausal symptoms in several ways:
- By improving insulin sensitivity, fasting can help regulate blood sugar. This regulation can support overall hormone balance; insulin is a key hormone that affects your body's metabolism and other hormone systems.¹⁰
- Fasting can reduce chronic inflammation, which can contribute to hormone imbalances and exacerbate menopausal symptoms like hot flashes and mood swings.¹¹
- Excess fat, especially around your waist, can produce excess estrogen and other hormones that may disrupt hormone balance. Fasting can contribute to hormone balance by helping with weight management.¹²
Brain health: Fasting can elevate brain-derived neurotrophic factor (BDNF) levels. This protein supports the growth, survival, and function of neurons in your brain. Higher BDNF levels can improve cognitive function, mood regulation, and neuroplasticity, or your brain's ability reorganize itself by forming new neural connections throughout life. This adaptability allows the brain to compensate for injury and disease, as well as to adjust to new situations and learn new things. These benefits help manage the risk of neurodegenerative diseases like dementia and enhance overall brain health.¹³
Bone health: Intermittent fasting increases growth hormone, which plays a key role in bone density and repairing bones.¹⁴ Fasting can also improve your body’s sensitivity to insulin and thyroid hormones, influencing bone health.¹⁵^{, 1}⁶ Chronic inflammation can harm bone health by promoting bone resorption (the process by which your body breaks down bone). Intermittent fasting can reduce markers of inflammation, which could indirectly support bone health.¹⁷

Is Fasting Different for Women?

Fasting affects women differently because of our unique hormone levels and body processes. While ongoing discussion among experts weighs the advantages and disadvantages of fasting for women, it can offer numerous benefits when you do it correctly.

Among those benefits, fasting can help balance hormones, particularly by making your body more responsive to insulin and keeping blood-sugar levels stable. This is especially important for women who have polycystic ovary syndrome (PCOS) or are at risk for diabetes.¹⁸

Fasting also boosts reproductive health, improving chances of fertility and easing symptoms related to hormone imbalances.¹⁹ Additionally, it can help women lose fat without losing muscle, especially combined with resistance training.²⁰

Studies have found that fasting not only supports reproductive and mental health but also helps prevent and manage certain cancers and bone-related conditions that are more common in women as they grow older. By lowering inflammation and other age-related factors, fasting protects against chronic diseases like osteoporosis and some cancers that often affect women as they grow older.²¹

When women fast correctly, they reap many metabolic and hormonal benefits.

“Having helped hundreds of men and women fast over the last five years, I've seen no difference between the sexes. If anything, women tend to do better [with fasting],” says Jason Fung, MD, The Complete Guide to Fasting.²²

How Fasting Impacts Specific Hormones

A well-designed fasting regimen can have a positive impact on many hormones. Among them include:

Insulin: Fasting makes your cells more sensitive to insulin, allowing them to absorb glucose from the bloodstream more effectively. This can help support blood-sugar levels and reduce your risk of insulin resistance.²³
Growth hormone: During fasting periods, your body increases the production of growth hormone. Besides its helpful impact on bone health, this hormone plays a role in fat metabolism, muscle growth, and repair processes. Elevated growth-hormone levels can contribute to improved body composition and metabolic health.²⁴
Cortisol: Fasting can help regulate cortisol, your body's primary stress hormone. Fasting may temporarily increase cortisol levels. Scientists consider fasting an acute stressor: a short-term, immediate event or situation that triggers your body's stress response. Acute stress isn't harmful and can make your body more resilient to difficult situations. However, fasting’s long-term effect is usually positive. Intermittent fasting may help reset your body's stress response, leading to more balanced cortisol levels.²⁵
Hunger hormones: Ghrelin, your hunger hormone, stimulates your appetite. Leptin has the opposite effect: this satiety hormone signals fullness. Intermittent fasting may help regulate these hormones, improving appetite control and reducing your overall food intake.²⁶

Potential Problems With Fasting

While intermittent fasting offers numerous benefits, there are also potential downsides. These issues are more likely to arise during longer fasts or when you're not following fasting protocols correctly. For most women, they aren’t an issue, although there are exceptions, such as with women who experience thyroid or adrenal dysfunction. Always talk with your functional-medicine doctor about specific concerns.

Menstrual disruptions: Intermittent fasting may cause menstrual irregularities or amenorrhea (missing periods) due to hormonal fluctuations, including changes in insulin and cortisol levels.²⁷
Bone health: Extended fasting periods, especially without adequate nutrient intake, can harm bone health and raise osteoporosis risk. This can be especially true for postmenopausal women, who have lower levels of bone-protecting estrogen.²⁸ To remedy this, make sure you’re getting enough bone-supporting nutrients in your diet, including calcium, magnesium, and vitamin D.*
Mood swings: Especially when you first start, fasting can trigger or worsen mental and emotional repercussions for some women, such as mood swings, irritability, and difficulty concentrating. These fluctuations tend to stabilize over time.²⁹

The following women should not fast:

Those who are severely malnourished or underweight
People with any eating disorder
Pregnant women
Breastfeeding women
Those with specific medical conditions (talk with your functional-medicine doctor if you have concerns)³⁰

“There are certainly potential problems women may face during fasting. But all these problems come up with men, too,” says Fung. “The studies on fasting, many going back over a hundred years, all show that it's safe for both sexes.”³¹

Ready to Begin Intermittent Fasting? Here’s How

If you're new, begin by implementing a 12-15 hour overnight fast. Starting with a shorter fasting window can help acclimate your body to the changes and make the transition smoother.

You’ll enjoy dinner by the plate, close up the kitchen for the evening, and then break your fast the following morning by 9 or 10 am. For most women, an overnight fast is effortless (because you’ll sleep for 7-9 hours) and incredibly effective. Breaking your fast with a protein-packed loaded smoothie is a great way to stabilize hormones and attack your day with vigor.

Maintaining steady blood-sugar levels is key to making fasting more accessible and sustainable. During eating windows, focus on consuming nutrient-dense meals with the magic trifecta of protein, healthy fats, and fiber-rich foods. Eating by the plate (as I call it) helps stabilize blood-sugar levels, promote satiety, and support overall well-being throughout fasting periods. One of my favorite ways to ensure you meet your macros is with Cronometer.

As you become more accustomed to intermittent fasting, you may experiment with longer fasting windows, such as the 16/8 method (where you fast 16 hours and eat within an 8-hour window). However, longer fasts should be approached cautiously, especially for beginners or women with specific health concerns. Many women find they do great with a shorter overnight fast.

Lifestyle factors are also critical to fasting success. Stress management and optimal sleep help manage hunger and minimize other pitfalls during intermittent fasting. Optimal protein intake and resistance training also support your results.

A Protein-First Approach Is Critical for Fasting Success

Most women aren't getting enough protein—and your needs increase with age. Insufficient protein can set you up for blood-sugar imbalances and other issues that can make fasting hours more challenging. Without optimal protein, you may experience fluctuations in energy levels, increased hunger, and difficulty maintaining satiety during fasting.

One simple shift can make your fasts easier and provide many other benefits: eat protein first. I've made optimal protein intake easy with my 7-Day Eat Protein First Challenge. You'll use the protein calculator to learn how much protein you should get daily. The challenge also provides a guide with tips, tricks, and a protein-first meal plan to help you successfully move to a higher-protein diet and reap the benefits.

If you've struggled with hunger, cravings, and other obstacles when you've fasted, now you know why. With optimal protein at every meal, fasting becomes easier and the cravings will be gone for good.

Join the FREE 7-Day Eat Protein First Challenge here.

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*These statements have not been evaluated by the Food & Drug Administration. Products mentioned are not intended to diagnose, treat, cure, or prevent any disease. The views in this blog by JJ Virgin should never be used as a substitute for professional medical advice. Please work with a healthcare practitioner concerning any medical problem or concern.