Fasting Affects Your Hormones Greatly

Dr. Eric Berg 08/12/2024

Fasting has gained popularity for its potential weight management and metabolic health benefits. But have you ever stopped to think about how fasting affects your hormones? It's actually quite a fascinating process.

When you fast, your body goes through a series of adaptations that influence your hormones in various ways, some positive and some a bit more challenging.

Understanding these fasting hormone effects is key to maximizing the potential benefits and navigating those temporary bumps along the way.

Demystifying Fasting Hormone Effects: A Look at the Science Behind the Changes

Let's unpack the science behind the most common fasting hormone effects:

Insulin: The Key to Unlocking Fat Burning

Insulin is often at the forefront of discussions about fasting, and for good reason. This hormone, produced by your pancreas, is essential for transporting glucose from the bloodstream into your cells for energy.

When you eat, especially refined carbohydrates and sugary treats, your insulin levels spike to deal with the incoming glucose.

But when you fast, insulin levels plummet. This drop sends a signal to your body to start tapping into stored fat for energy, which can be incredibly beneficial for weight loss and reducing levels of inflammation.

Lower insulin levels also mean less inflammation, which is linked to many chronic diseases. This hormonal shift is a cornerstone of how fasting can positively impact your metabolic health.

Growth Hormone: Your Body's Anti-Aging Ally

Fasting also increases the production of human growth hormone (HGH). Known as the "fountain of youth" hormone, HGH plays a vital role in cell regeneration, muscle growth, and maintaining youthful vigor.

As we age, our natural HGH production declines, contributing to muscle loss, wrinkles, and other signs of aging.

By incorporating regular fasting, we may help counter these effects by naturally boosting HGH. A small study found that a 24-hour fast can increase HGH levels in men by up to 2,000%, and by up to 1,300% in women.

While more research is always welcome, these initial findings suggest that fasting's benefits go far beyond just weight loss.

Glucagon: Your Liver's Secret Weapon

Glucagon is often considered insulin's lesser-known counterpart, but it's just as crucial for regulating blood sugar levels during your eating window.

Think of it this way: when insulin brings blood sugar down, glucagon brings it up by signaling your liver to release stored glucose (called glycogen).

This process prevents dangerous blood sugar drops, particularly when fasting, and is one of the effects on hormones that makes time-restricted eating possible.

Adrenaline and Cortisol: Managing Those Mid-Fasting Jitters

You may be familiar with these hormones as your body's stress response team, and that's true during a fast. Your body senses a drop in available glucose from food, which it initially interprets as a potential threat.

This triggers a temporary increase in adrenaline and cortisol to release stored glucose for energy and keep your brain functioning optimally. This is what some people call the "fasting hump," and it can affect hormone levels in an unpleasant way.

However, this effect on hormone levels is temporary, and as your body adapts to fasting, these spikes in adrenaline and cortisol will lessen. Drinking plenty of water and engaging in light activity can help to minimize these jitters.

For women, this is an important thing to consider when evaluating how fasting may affect hormone levels related to reproduction.

Leptin: The Appetite Regulator

Leptin plays a critical role in regulating your appetite and sending signals to your brain that you've had enough to eat. Leptin levels usually decrease during a fast, which can lead to increased feelings of fullness and reduced overall calorie intake.

However, long-term fasting may interfere with leptin levels and production. This is something to consider when deciding how long to fast. Make sure your doctor knows your plans before starting intermittent fasting or any other diet type.

Thyroid pain

Thyroid Hormones: The Metabolic Regulators

Fasting has a profound effect on thyroid hormone levels, including:

T3 (Triiodothyronine): Your body's primary metabolic regulator. During a fast, T3 levels may slightly decrease as your body adapts to using stored fat for fuel. However, this doesn’t mean your metabolism is slowing down. In fact, this metabolic shift contributes to improved insulin sensitivity.
Reverse T3 (rT3): A less active form of T3 that can interfere with your metabolism. During fasting, your body often converts T4 (a thyroid hormone precursor) to rT3. This is thought to be a protective mechanism to conserve energy, but the long-term effects on thyroid function are not yet completely understood.

Because there is limited information available about how fasting blood sugar levels and altered thyroid hormones might impact those who are pregnant or breastfeeding, fasting is not recommended for these individuals.

Fasting and Women's Hormones

Fasting can have specific effects on reproductive hormones in women, influencing menstrual cycles and overall reproductive health. Here’s a closer look at how fasting may affect women’s hormones:

Menstrual Cycle Changes

Fasting can impact the menstrual cycle due to its effects on hormones like estrogen and progesterone. Some women report shorter cycles, longer cycles, or even missed periods, especially with prolonged or very calorie-restrictive fasts.

It's essential to listen to your body and consult with your doctor if you experience significant menstrual irregularities while fasting. Maintaining adequate calorie intake and avoiding excessive calorie restriction is crucial for hormonal balance.

Impact on Fertility

While occasional fasting is unlikely to cause significant issues for most women trying to conceive, prolonged or extreme fasting may interfere with ovulation.

For women undergoing fertility treatments, it’s best to consult with a reproductive endocrinologist to determine the most appropriate fasting approach.

Polycystic Ovary Syndrome (PCOS)

Intermittent fasting has shown potential benefits for women with PCOS. Studies suggest that alternate-day fasting and time-restricted feeding may help improve insulin sensitivity, reduce testosterone levels, and regulate menstrual cycles in women with PCOS.

However, more research is needed, and working closely with a healthcare provider experienced in managing PCOS is crucial.

Hormonal Shifts

Explores the significant changes your body undergoes during an extended fast. As you progress through a 7-day fast, your body experiences a series of hormonal adjustments that impact everything from metabolism to energy levels.

In the early stages, insulin levels drop significantly, promoting fat burning as the primary energy source. Human growth hormone (HGH) levels increase, supporting muscle preservation and fat loss.

As the fast continues, cortisol levels may rise, helping your body manage stress but also requiring careful attention to avoid negative effects like muscle breakdown.

Leptin and ghrelin, the hormones responsible for hunger and satiety, also adjust, potentially reducing appetite over time.

Understanding these hormonal shifts during a 7-day fast can help you navigate the process more effectively, ensuring that you achieve the benefits while minimizing potential drawbacks.

Conclusion

The effects of fasting on hormones are complex.

While fasting can provide health benefits by positively influencing hormones like insulin, growth hormone, and glucagon, it’s crucial to approach fasting with caution and work closely with a healthcare professional, especially if you have any underlying health conditions.

Pay close attention to your body's signals and any changes you experience. Remember, achieving optimal health is not just about quick fixes but rather a holistic journey that considers the intricate interplay within our bodies.