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The stages of fasting, a complete mind-body reset. Fasting is powerful, and when combined with advanced detox protocols, it becomes truly transformational.
Fasting has become one of the most respected tools in the world of wellness, and at Amity Wellness, we’ve been witnessing its potential firsthand for many years. From gentle intermittent fasting to four-day juice cleanses and longer full fasting retreats, fasting offers far more than a passing trend. It invites the body to return to its natural wisdom.
While fasting can unlock powerful healing, it’s not always easy. Some stages can bring physical discomfort, emotional waves, or unexpected cravings, especially if it’s your first time.
That’s why at Amity Wellness, you’re never left to figure it out alone. Our experienced cleansing specialists are here to guide you with modifications, detox protocols, and simple tips to ease the process. Whether it’s adjusting your fasting window, adding electrolytes, or just offering a moment of encouragement, we meet you where you are so you can move through each stage with confidence and care.
In this article, we’ll explore what can happen inside the body throughout different stages of fasting and how brain chemistry and hormones can potentially respond.
12 Hours – Blood Sugar Reset Begins
Around 12 hours after your last meal, your body begins to use up stored glucose. Insulin levels drop, and your metabolism starts to shift gears as the body starts preparing to transition from burning sugar to burning fat. Emotionally, you might notice habitual patterns around snacking or emotional eating more clearly. Morning yoga at Amity Wellness helps lymphatic flow, while botanical cleansing shakes will curb cravings and ease the digestive system into fasting mode.
13–15 Hours – The Switch to Fat Burning and BDNF Production
Around 15 hours, ketone production begins for most people. As glycogen stores deplete and ketone production begins, the brain shifts from using glucose to burning beta-hydroxybutyrate (BHB), a ketone that has the power to stimulate BDNF (Brain-Derived Neurotrophic Factor), a powerful protein that supports neuroplasticity, learning, memory, and emotional resilience. This boost in BDNF can be especially beneficial for women experiencing brain fog, anxiety, or low mood, particularly during perimenopause or postmenopause.
You may notice reduced cravings, more stable energy, and a sense of empowerment. This stage also plays a key role in estrogen detox. Our FIR infrared Inflammation Pod and oxygen therapy can amplify circulation and support gentle detoxification as this metabolic switch begins.
16–18 Hours – Cellular Cleanup, Calm Focus, and Brain Chemistry Reset
As the fast deepens, the body enters a critical phase of renewal. Nutritional ketosis is often established when blood ketone levels (BHB) rise above 0.5 mmol/L, and fat becomes the primary fuel source.
Autophagy begins, which is a cellular housekeeping process that clears out old, damaged components and starts breaking down senescent cells, often called “zombie cells.” These are cells that no longer function properly but linger in the body, contributing to inflammation and aging.
At the same time, ketone production increases, particularly beta-hydroxybutyrate (BHB), which fuels the brain and begins to influence your mood and mental state. BHB enhances GABA activity, the brain’s calming neurotransmitter, helping to reduce anxiety and emotional reactivity.
You may also experience a dopamine reset, where the brain becomes more satisfied with less stimulation. Many guests report feeling grounded, focused, and emotionally lighter during this stage.
At Amity Wellness, we support these shifts with daily wellness activities, restorative massage and colon hydrotherapy, which help activate detox pathways, ease tension, and reduce the physical discomfort that can sometimes accompany deeper detoxification.
24 Hours – Gut Repair, Emotional Calm, and Hormone Rebalance
At the 24-hour mark, your digestive system finally gets a complete rest. With no new food coming in, your gut lining begins to repair, inflammation eases, and your microbiome starts to rebalance, supporting better digestion, immunity, and nutrient absorption.
This stage also activates key repair processes in the gut, including improvements in intestinal stem cell function. While full-body stem cell regeneration takes place later in the fast, this early phase helps lay the foundation for healing conditions like leaky gut, food sensitivities, and bloating. Some guests also notice a reduction in histamine reactions, which may show up as clearer skin, less congestion, or improved mental clarity.
As the gut heals, serotonin production naturally increases, often bringing more emotional stability and a calmer mood. This phase also begins to reset hunger and satiety hormones like ghrelin and leptin, helping to restore a healthier, more intuitive relationship with food.
At Amity Wellness, we support this critical stage with daily colonic irrigation, daily inflammation pod using FIR sauna therapy, and gentle detox supplements that assist the liver, reduce the toxic load, and accelerate your body’s natural healing response.
36–48 Hours – Cellular Regeneration, Metabolic Reset, and Emotional Release
This is one of the most powerful windows in the fasting process. Around this time, system-wide stem cell activation can begin, supporting the repair of tissues in the gut, joints, skin, and brain.
While a more advanced immune system reboot potentially occurs closer to 72 hours, this stage lays the foundation, clearing out dysfunctional cells and initiating deep internal repair.
Your body is now highly efficient at burning fat for fuel. Insulin levels reach their lowest point, increasing metabolic flexibility and supporting long-term blood sugar balance. Ketone levels peak, fueling the brain and stimulating key longevity and brain-health pathways, including BDNF for cognitive clarity and GABA for emotional calm.
Guests often describe this stage as a turning point. Physically, joint discomfort may ease and energy becomes more sustained. Mentally, there’s often a profound sense of clarity. Emotionally, it’s common to experience reflection or even emotional release, as fasting brings a sense of stillness and inner awareness.
72 Hours – Immune Reboot, Brain Clarity, and Visceral Fat Reduction
At the 72-hour mark, your body initiates a profound internal reset. Damaged immune cells can begin to be cleared out, and stem cells begin generating new white blood cells, helping to renew and strengthen your immune system from the inside out. This process can support immunity, reduce chronic inflammation, and improve resilience over time.
At this point in the fast, insulin is at its lowest, allowing the body to become highly efficient at burning visceral fat (the deep abdominal fat stored around your organs). This type of fat is often linked to disease and hormone imbalances, particularly insulin resistance and estrogen dominance, which makes this stage especially valuable for women struggling with stubborn belly fat or weight loss resistance in perimenopause and postmenopause. Ketone production peaks here, continuing to fuel the brain with clean energy.
Many guests report heightened focus, emotional steadiness, and even a sense of peaceful clarity. The nervous system becomes more regulated, and with inflammation reduced, the mind and body feel lighter and more balanced.
Beyond Day 5 – Full-System Renewal, and Deep Clarity
When fasting continues beyond five days, the body may enter a deep state of cellular renewal. Longevity pathways are further activated, inflammation continues to decline, and cellular repair can continue in the brain, joints, skin, gut, and immune system.
This phase can offer benefits like enhanced fat metabolism, reduced inflammation, and metabolic flexibility, particularly for postmenopausal women. However, due to the potential impact on progesterone and stress hormones, we recommend longer fasts be approached cautiously and only a couple of times per year (in the follicular phase for women still cycling).
Many people also report enhanced energy, better sleep, emotional lightness, and clearer thinking during this phase. Emotionally, this stage often brings a deep sense of calm, increased intuition, and a stronger connection to self.
At Amity Wellness, we support this phase with continued detox support and ample space for integration and reflection, allowing the benefits of fasting to unfold fully and sustainably.
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Why We Cap Full Fasts at 10 Days: A Gentle Boundary for Hormonal and Metabolic Health
While fasting can be profoundly healing, we believe in a careful approach rooted in wisdom, safety, and experience. At Amity Wellness, we cap all full fasting protocols at 10 days maximum. Not because longer fasts can’t offer benefits, but because we’ve found, through years of practice, that this is the optimal window for effective transformation without overburdening the body.
Our modified fasting programs are designed with care to support the body’s detox processes rather than deplete them. Using a combination of botanicals, chelating agents, therapeutic shakes, liver-supportive herbs, detox protocols, and mindful movement, we help you access the full benefits of fasting while respecting the natural intelligence and limits of your physiology.
Fasting beyond 10 days, can potentially place strain on the adrenal system, thyroid function, and hormonal equilibrium (particularly in women). We prefer to protect the delicate hormonal and metabolic systems while still allowing time for deep detox, repair, and reset. We view fasting as a rest and cyclical healing tool that must be followed by intelligent refeeding, restoration, and nourishment.
Finding the Right Path for You
Fasting is a powerful tool for healing, but it’s not suitable for everyone. That’s why every guest at Amity Wellness begins with a thorough pre-screening process, ensuring we fully understand your needs, goals, and any contraindications before tailoring your experience.
We offer a variety of cleansing options to meet you exactly where you are. Whether you’re drawn to a nourishing raw vegan cleanse, intermittent fasting, juice cleansing, or a more intense full fast, our programs are designed to be flexible, supported, and personalized.
What makes our approach truly transformational is the combination of fasting protocols with targeted detox therapies, a synergy we believe represents the most powerful healing modality of the 21st century. When the body is given the space to rest, reset, and release, deep healing becomes not only possible but inevitable.
Join us at Amity Wellness in Phuket—where fasting becomes a journey of healing, clarity, and renewal. For more information about our wellness retreat in Phuket, Thailand, visit www.amitywellness.com
Disclaimer: This article is for educational purposes only. It does not constitute medical advice, does not guarantee results, and does not make any health or treatment claims. Individual experiences may vary. Please consult your healthcare provider before starting any fasting or detox program.
Want to geek out on some of the Science involving the various stages of fasting?
- Metabolic Switching and Ketosis
• Sutton, E. F., et al. (2018). Time-Restricted Feeding Improves Insulin Sensitivity and Blood Pressure in Men with Prediabetes. Cell Metabolism.
• Newman, J. C., & Verdin, E. (2017). β-Hydroxybutyrate: A Signaling Metabolite. Nature Reviews Molecular Cell Biology.
• Michalsen, A., et al. (2024). Long-term fasting-induced ketosis in 1,610 subjects. Nutrients. PMC11206495 (https://pmc.ncbi.nlm.nih.gov/articles/PMC11206495/)
• Cahill, G. F. Jr. (2006). Fuel metabolism in starvation. Annual Review of Nutrition, 26:1–22. PubMed - Autophagy and Cellular Cleanup
• Mizushima, N., & Komatsu, M. (2011). Autophagy: Renovation of Cells and Tissues. Cell.
• Yoshinori Ohsumi. Nobel Prize in Physiology or Medicine, 2016. Autophagy mechanisms. nobelprize.org - Stem Cell Activation and Immune Regeneration
• Brandhorst, S., et al. (2015). Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration. Cell Metabolism.
• Cheng, C. W., et al. (2014). Prolonged Fasting Promotes Hematopoietic Stem Cell Regeneration. Cell Stem Cell.PMC4102383
• Yousefi, M., et al. (2018). Fasting boosts regenerative capacity of intestinal stem cells. MIT News. MIT - Brain Health and BDNF
• Baik, S. H., et al. (2023). Intermittent fasting promotes neurogenesis and enhances BDNF. Frontiers in Aging.Frontiers. In relation to brain health, various stages of fasting may enhance BDNF levels as demonstrated in recent studies.
• de Cabo, R., & Mattson, M. P. (2019). Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine, 381:2541–51. NEJM - Hormonal Health and Women’s Physiology
• Hutchison, A. T., et al. (2022). Intermittent fasting and reproductive hormone regulation. Obesity, 30(5):1025–1034. PMC9182756
• UIC Study (2022). Intermittent fasting’s impact on female hormones. University of Illinois Chicago News. UIC. In terms of hormonal health, understanding the stages of fasting helps illustrate its impact on women’s physiology. - Practitioner-Informed Protocols
• Longo, V. D. (2018). The Longevity Diet: Discover the New Science Behind Stem Cell Activation and Regeneration to Slow Aging, Fight Disease, and Optimise Weight. Avery.
• Fung, J. (2016). The Obesity Code: Unlocking the Secrets of Weight Loss. Greystone Books.
• Panda, S. (2018). The Circadian Code: Lose Weight, Supercharge Your Energy, and Transform Your Health from Morning to Midnight. Rodale Books.
• Pelz, M. (2022). Fast Like a Girl: A Woman’s Guide to Using the Healing Power of Fasting to Burn Fat, Boost Energy, and Balance Hormones. Hay House. Practitioners have developed fasting protocols by understanding the stages involved.
