The Link Between Fasting and Hormone Balance

For individuals who want to improve their well-being, fasting has become a popular dietary and wellness approach.

Beyond benefits like weight loss and improved brain function, fasting has been shown to have a significant impact on our hormonal balance.

Although fasting can improve hormonal processes in the body, it’s important to know how to implement this approach to avoid experiencing adverse reactions.

In this article, we’ll take a closer look at how fasting works, why it has such a big impact on hormones, and what you need to do to prevent health complications.

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How Does Fasting Work?

Fasting is a time-restricted dietary approach where you avoid eating for a certain period of time. There are many different types of fasting, but they all affect the body in similar ways.

It mainly causes a series of physiological and metabolic changes in the body due to an absence of nutrients.

When you stop eating, the body begins to use alternative energy sources to help you get through the day.

In most cases, the body stops using glycogen — its primary source of energy — and starts tapping into stored fat reserves.

This process is called lipolysis and causes fatty acids to be released into the bloodstream, leading to a state of ketosis.

When the body is in ketosis, you may start to experience higher levels of energy and more rapid weight loss as the body uses stored fat as fuel during this phase.

Key Hormones Involved in Metabolism

Hormones play a vital role in regulating metabolism and overall health. In this section, we’ll take a closer look at the ones central to these processes.


Insulin is one of the most well-known hormones, and it’s responsible for regulating blood sugar levels.

It’s produced by the pancreas and helps the body absorb glucose (sugar), which is either used as energy or stored for later use.

Insulin also helps store excess glucose as glycogen in the liver and muscles. As mentioned before, glycogen is one of the body’s primary energy sources.

Key Point: What Happens to Insulin When You Fast?

Fasting causes a significant drop in insulin levels. With little to no food intake, there is less sugar in your bloodstream, and the pancreas reduces its insulin production.

Lower insulin levels signal the body to switch from using glucose for energy to using stored fat.

This process promotes fat breakdown and improves insulin sensitivity or resistance, which can aid weight loss over time. Insulin resistance can also reduce oxidative stress.


Similar to insulin, glucagon is also produced by the pancreas and it affects blood sugar levels.

However, glucagon produces the sugar that insulin helps absorb. It does this by stimulating the liver to convert stored glycogen into glucose.

This glucose is then released into the bloodstream to provide an easily accessible source of energy.

Key Point: What Happens to Glucagon When You Fast?

During fasting, glucagon levels may rise to stimulate the liver to release glucose. This is done to help the body maintain stable blood sugar levels and ensure a continuous supply of energy.

While the body uses stored fat for energy, the adjustment of glucagon levels fuels other processes — such as brain function — that are reliant on glucose.


Leptin is referred to as the "satiety hormone" because it plays a crucial role in regulating appetite and body weight.

When this hormone is produced by the fat cells, the body’s leptin levels rise and signal to the brain that you are full. As these levels decrease, you will start to feel hungry again.

Key Point: What Happens to Leptin When You Fast?

Leptin levels tend to decrease during fasting – especially when you start losing weight.

These lower levels signal to the brain that the body’s energy reserves are depleting, which may increase your appetite and leave you feeling very hungry.

Over time, the body will get used to fasting periods, and leptin levels tend to stabilize. This may help improve appetite control.


Ghrelin — also known as the "hunger hormone” — is produced in the stomach and stimulates appetite.

Its levels tend to rise before meals, signaling hunger to the brain. During fasting or periods of calorie restriction, ghrelin levels typically increase, and you feel the need to eat.

Key Point: What Happens to Ghrelin When You Fast?

During the initial phases of fasting, increased ghrelin levels may intensify feelings of hunger. However, as the body adjusts to periods without food, these levels decrease.

The reduction in ghrelin can help improve appetite control, which can be beneficial for people who want to eat less to manage their calorie intake and lose weight.

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Cortisol is the primary stress hormone released by the adrenal glands.

While cortisol is typically produced in response to stress, it may also be triggered by low blood sugar levels.

When the body experiences high levels of cortisol for a prolonged amount of time, it can have negative health implications.

Cortisol can have an adverse reaction on various body functions, including metabolism, immune response, and blood pressure regulation.

Key Point: What Happens to Cortisol When You Fast?

Fasting can cause complex changes to cortisol. Short-term fasting can lead to an increase in cortisol levels as a natural response to stress and low blood sugar.

However, extended periods of fasting may cause cortisol levels to drop. This can potentially decrease your risk of developing the stress-related health issues mentioned above.

Fasting’s Impact on Sex Hormones

Fasting has a complex influence on the primary reproductive hormones estrogen, progesterone, and testosterone.

These hormones play an important role in our reproductive health, so understanding how your dietary approaches can impact them is key.

Balancing estrogen levels

Excess body fat is commonly associated with elevated estrogen levels. This is because fat tissues can produce and store this hormone.

Fasting tends to reduce excess body fat — especially when you lose weight — which can decrease estrogen levels.

If you suffer from high levels of estrogen — which tends to be associated with various health issues, including hormone-related cancer — fasting can help you achieve a better balance.

However, it’s important to monitor your estrogen if you decide to fast, as chronically low estrogen levels can negatively affect your reproductive system and fertility.

Optimizing testosterone

Some studies suggest that techniques like intermittent fasting — a time-restricted method of eating — in particular, may have a positive impact on testosterone levels.

Testosterone is an essential hormone that influences muscle mass, bone density, mood, and libido.

Intermittent fasting affects testosterone production and may reduce normal hormone levels., This can be beneficial for individuals who want to increase their lean muscle mass.

Just like with estrogen, it’s also important to keep an eye on your testosterone levels when you fast.

Prolonged periods of high testosterone levels can raise your cholesterol, increasing your risk of cardiovascular disease, heart attack, and stroke.

Menstrual regularity

For women, fasting can have implications for menstrual regularity and female hormones — particularly the luteinizing hormone that impacts ovulation.

While some women may have more regular periods, fasting can cause disruptions for others — especially if you’re following an intense restrictive diet.

Consuming extremely few calories and exercising excessively during fasting can also lead to hormonal imbalances, which may affect your menstrual cycle.

That’s why it’s essential to consider your individual needs before implementing an aggressive regime.

Fasting’s Impact on Thyroid Function

A common concern with fasting is its potential impact on thyroid hormones — particularly the thyroid gland and its ability to regulate metabolism.

It’s important to note that short-term or occasional fasting is unlikely to have a detrimental effect on thyroid functions.

Some studies also suggest that brief fasting periods have certain health benefits for thyroid health, but more research is needed.

When it comes to prolonged or extreme fasting regimes, it’s crucial to take thyroid hormones into account.

Extended periods of calorie restriction — especially when combined with severe energy deficits — can suppress thyroid hormone production.

This can cause the metabolism to slow down, which may lead to weight gain and extreme fatigue. Long-term suppression can also negatively affect your cardiovascular and bone health and increase your risk of developing metabolic syndrome.

Stress Response and Fasting

Fasting may have a notable impact on the body’s stress response system, also known as the hypothalamic-pituitary-adrenal (HPA) axis.

The HPA axis is a complex network of interactions between the brain, and the pituitary and adrenal glands.

This network is responsible for controlling how the body reacts to stress and maintaining various physiological processes.

Fasting and the HPA axis

When the body is under stress — whether physical, emotional, or related to nutrient deprivation — the HPA axis is activated.

This triggers the release of cortisol to help the body manage stress more effectively.

Remember that the nature of the body’s stress response to fasting is different from its response to an environment that puts physical or emotional stress on us

Fasting prompts a more controlled response where cortisol levels return to normal relatively quickly after the initial spike.

Over time, this can promote stress resilience and help the body better adapt to uncomfortable situations.

Promoting Hormonal Balance and Health Through Fasting

Fasting isn’t necessarily a one-size-fits-all solution, so its effectiveness and overall impact can vary.

To ensure that you get the most out of this dietary approach without negatively impacting your hormones, a gradual approach is key.

This includes implementing short-term and controlled fasting periods — such as intermittent fasting — that are generally considered safe for most people.

These methods allow you to get the benefits of fasting without pushing your body to extremes.

As we’ve mentioned before, prolonged fasting can have a negative impact on your overall health.

It usually triggers significant hormonal changes — including reduced thyroid function, imbalanced sex hormones, and heightened stress responses — that can affect your quality of life.

Over time, these changes can also result in fatigue, muscle loss, and improper metabolic function. Women may also experience irregular menstrual cycles.

That’s why it’s important to recognize individual factors — like age, gender, activity levels, and underlying health conditions — before you implement a new dietary approach.

It’s also important to speak to your doctor before you start fasting to determine if it’s a safe and effective option for you and your health goals.

Where Can You Learn More About Fasting and Hormones?

If you’re concerned about fasting and how it may affect your hormonal balance, LifeMD is here to help.

A team of medical professionals can assist you with information and provide guidance on how to effectively implement fasting — all from the comfort of your home.

Make an appointment with LifeMD to learn more about fasting, hormonal balance, and healthy ways to manage your weight.

LifeMD makes it easy to stay on top of your health because talking to a doctor, filling your prescriptions, getting your labs done—and more—are all easy and cost-effective. Come discover a healthcare solution built around you and your life.

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This article is intended for informational purposes only and should not be considered medical advice. Consult a healthcare professional or call a doctor in the case of a medical emergency.

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