Fasting and Hormonal Balance: How Water and Rest Influences the Endocrine System

2 days ago

7 min read

Water Fasting: Benefits, Risks, and What Happens After 3, 5, 7, 10 and 14 Days

Many chronic health conditions are closely connected to hormonal regulation. Type 2 diabetes, high blood pressure, obesity, menstrual pain (dysmenorrhea), menopause-related symptoms, hypothyroidism, Hashimoto's thyroiditis, Insomnia, depression, anxiety, and chronic stress-related symptoms all involve, in different ways, the endocrine system. Through our clinical experience with supervised fasting at Back to the Garden, we have observed meaningful improvements in individuals dealing with all of these conditions.

This raises the question: How does water fasting affect our hormones and the endocrine system as a whole?

The answer begins with one of the most fundamental requirements for health: REST.

We often think of rest as sleeping or avoiding physical activity. However, true rest goes much deeper. It involves reducing the demands placed on our physical, mental, and emotional systems while allowing the body to redirect its resources toward adaptation and recovery. Water Fasting provides a unique opportunity to realize this precise environment. When we stop eating, the digestive system receives a break from processing incoming food, insulin levels decline, stored energy becomes available, and numerous hormonal pathways begin to adjust. When fasting is combined with physical relaxation, adequate sleep, meditation, mental quiet, and spiritual reflection, it becomes more than an intervention. It becomes an opportunity to step away from the constant stimulation of daily life and to allow our physiology and psychology to adapt and fine tune simultaneously. These adaptations inherently balance our hormones.

Fasting is not simply about going without food. It is about creating an environment where the body can rest, adapt, and support its natural healing processes.

How Fasting Affects Our Hormones

The endocrine system is a network of glands and tissues that produce hormones responsible for regulating metabolism, blood sugar, stress, reproduction, energy, and countless other functions. These hormones work together. Changes in one system can influence several others. Fasting activates a coordinated hormonal response that allows the body to transition from using recently consumed food to utilizing stored energy. Many of these changes improve metabolic health. Others are temporary adaptations that help us function without exogenous nutrients.

Understanding this distinction is essential. For a detailed explanation of the physiological stages of fasting, read our comprehensive article: Water Fasting: Benefits, Risks, and What Happens After 3, 5, 7, 10, and 14 Days

1. Insulin: Improving Metabolic Health

Insulin is one of the hormones most directly influenced by fasting. When we eat, insulin helps transport glucose into our cells and promotes energy storage. In individuals with insulin resistance, the body requires increasingly higher amounts of insulin to regulate blood sugar. This contributes to conditions such as type 2 diabetes, obesity, and metabolic dysfunction. During fasting, insulin levels decline, allowing the body to rely increasingly on stored fat for energy.

A 2018 study published in Cell Metabolism demonstrated that early time-restricted eating improved insulin sensitivity, blood pressure, and markers of oxidative stress in men with prediabetes, even without significant weight loss. This suggests that some metabolic benefits of fasting may occur independently of changes in body weight.

The benefit: Improved insulin regulation can positively influence blood sugar control, metabolic flexibility, and several conditions associated with insulin resistance. Study: Sutton et al., Cell Metabolism, 2018.

2. IGF-1: From Growth to Cellular Maintenance

Insulin-like growth factor 1 (IGF-1) is involved in cellular growth, tissue development, and repair. During periods of abundant nutrition, IGF-1 supports growth-related processes. During prolonged fasting, IGF-1 activity may decrease, reflecting a shift in the body's metabolic priorities. Research examining prolonged fasting has documented changes in IGF-1, growth hormone, and other nutrient-sensitive hormonal pathways. These changes are particularly interesting because nutrient-sensing pathways influence cellular maintenance, metabolic adaptation, and processes associated with aging.

A 2024 study published in Nature Metabolism found widespread changes in circulating proteins during a seven-day water-only fast, with many systemic responses becoming evident after approximately three days. Although this research does not establish that prolonged fasting prevents aging or disease, it illustrates the remarkable biological changes that occur when the body abstains from food.

The benefit: Temporary reductions in growth-related signaling may support adaptive cellular processes, which may affect various chronic conditions including many types of cancer and other undesired growths such as cysts, myxomas, fibromas, and other tumors. although the long-term clinical significance remains under investigation. Studies: Pietzner et al., Nature Metabolism, 2024; research on IGF-1 and prolonged fasting.

3. Thyroid Hormones: Conserving Energy

The thyroid regulates metabolism, body temperature, and energy expenditure. During prolonged fasting, levels of active thyroid hormone T3 generally decline as the body adapts to reduced energy availability. This response helps regulate energy expenditure during periods without food. For individuals with hypothyroidism or Hashimoto's thyroiditis, fasting may influence metabolic and hormonal parameters.

At Clinica Back to the Garden we have seen a large number of patients come through the fasting center whom suffered from thyroid conditions and most have been highly successful in improving thyroid health. View testimonials section.

The benefit: Fasting demonstrates the endocrine system's remarkable ability to adjust metabolic activity to changing nutritional conditions. Making our endocrine connections more flexible and resilient.

4. Cortisol: The Relationship Between Stress and Rest

Cortisol plays an important role in maintaining blood sugar, regulating blood pressure, and helping the body respond to stress. Interestingly, fasting can temporarily increase cortisol, especially during its initial stages. This is a normal part of the body's response to reduced energy intake, but it also reminds us that fasting itself can be a good physiological stressor. A systematic review found that fasting produces an acute increase in circulating cortisol. This is precisely why we believe the environment in which fasting takes place is so important. At Back to the Garden, we emphasize complete physical rest, quality sleep, meditation, emotional relaxation, and reducing unnecessary stimulation. Our intention is to minimize additional stress while the body undergoes its metabolic adaptations. Changes in cortisol levels during fasting support the mobilization of stored energy, help to maintain energy availability, regulate inflammation and immune activity and support the body's adaptive stress response.

The benefit: Cortisol is needed during profound recovery, catabolism of excesses in the system and efficient detoxification and elimination of old and senescent cellular material.

5. Estrogen, Progesterone, and Testosterone

Reproductive hormones are also influenced by nutritional status and metabolic health. Estrogen, progesterone, and testosterone help regulate reproductive function, bone health, body composition, and numerous other physiological processes. Fasting can influence these hormones indirectly through changes in insulin sensitivity, body fat, and energy availability. For example, improving insulin resistance and excess body fat may benefit certain hormonal disturbances associated with obesity or polycystic ovary syndrome (PCOS). However, research has not established that fasting consistently increases estrogen or progesterone or restores reproductive hormone levels. Fasting appears to have more of a balancing effect. In some situations, particularly when energy intake becomes chronically inadequate, fasting may suppress reproductive hormone activity. A 2022 review of human fasting trials found that reproductive hormone responses varied according to sex, body composition, and fasting protocol.

At Clinica Back to the Garden we consistently see success when fasting is used as an intervention, but also as a diagnostic tool. A Water Fast is, in many cases, the appropriate 1st line of conservative care when an endocrine system imbalance is identified. FREE CONSULT

Why Rest Is So Important for the Endocrine System

Perhaps the most important lesson from fasting is that the body requires periods of recovery just as much as periods of activity. Our endocrine system responds continuously to food intake, sleep, emotional stress, physical activity, and environmental stimulation. In modern life, many individuals are constantly eating, working, thinking, and responding to external demands, often without providing sufficient opportunities for rest. Fasting creates an opportunity to interrupt this pattern and make the most of a purposeful restful periods.

Digestive activity associated with meals decreases. Metabolic pathways shift. Insulin secretion falls. And when the fast is accompanied by relaxation and reduced stimulation, the nervous system may also experience a more restorative environment. The parasympathetic nervous system, often associated with rest and recovery, is especially relevant. Some research involving modified fasting protocols has identified changes in autonomic nervous system activity consistent with greater parasympathetic influence later in the fasting period.

This is why rest during fasting must be intentional.

At our fasting center, we emphasize several dimensions of rest:

Physical rest: Reducing exertion and allowing the body to conserve energy.
Digestive rest: Temporarily removing the continuous demand to process incoming meals.
Mental and emotional rest: Reducing stimulation, stress, and unnecessary responsibilities.
Spiritual rest: Creating space for meditation, reflection, and a deeper connection with ourselves and the natural world.

We believe this comprehensive experience is what makes supervised fasting fundamentally different from simply skipping meals while continuing a demanding daily routine.

It is an opportunity to give the whole person—not just the digestive system—a period of intentional rest.

The Power of Complete Rest

One of the greatest lessons we have learned through our experience with fasting is that health is not always achieved by doing more. Sometimes, we need to do less. Less eating. Less stimulation. Less exertion. Less distraction. More sleep. More stillness. More reflection. More connection with nature and ourselves. When fasting is practiced appropriately, with proper screening, supervision, and rest, it offers a unique opportunity to step away from our regular routines and observe the body's extraordinary capacity to adapt. This is why extended water-only fasting should be undertaken only with appropriate clinical supervision and a carefully planned refeeding process. For a detailed explanation of the physiological stages of fasting, read our comprehensive article: Water Fasting: Benefits, Risks, and What Happens After 3, 5, 7, 10, and 14 Days

To PLAN YOUR VISIT TO Back to the Garden -> click here

Scientific References

Sutton EF, et al. (2018). Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism. https://doi.org/10.1016/j.cmet.2018.04.010
Pietzner M, et al. (2024). Systemic proteome adaptations to 7-day complete caloric restriction in humans. Nature Metabolism. https://pubmed.ncbi.nlm.nih.gov/38429390/
Ezpeleta M, et al. (2024). Efficacy and safety of prolonged water fasting: a narrative review of human trials.Nutrition Reviews. https://pubmed.ncbi.nlm.nih.gov/37377031/
Cienfuegos S, et al. (2022). Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials. Nutrients. https://pubmed.ncbi.nlm.nih.gov/35684143/
Systematic review and meta-analysis reveals acutely elevated plasma cortisol following fasting but not less severe calorie restriction. (2016). https://pubmed.ncbi.nlm.nih.gov/26586092/
Goldhamer A, et al. (2001). Medically supervised water-only fasting in the treatment of hypertension. Journal of Manipulative and Physiological Therapeutics. https://pubmed.ncbi.nlm.nih.gov/11416824/
Long-term fasting-induced parasympathetic and sympathetic autonomic nervous system modulation in a subgroup of the GENESIS study. (2025). https://pubmed.ncbi.nlm.nih.gov/40634681/