Fasting as a tool for health promotion

Fasting is no longer viewed only as a method of weight control. It is an effective tool for activating the body’s regenerative processes, improving hormonal balance, metabolism, immunity, and preventing chronic diseases. Across cultures and religions, fasting represents an ancient practice that supports cleansing and health. In this article, we will take a closer look at fasting and its various forms, explain the mechanisms through which it supports our health and immune system, and highlight the specific aspects of fasting for women.

What will you learn in this article?

1. What is fasting?
2. Why practice fasting regularly?
3. How does the body respond to a break from food?
4. How to start fasting
5. Specifics of fasting for women
6. Who should avoid fasting entirely?
7. Conclusion
8. Key takeaways

What is fasting?

Fasting is a period during which a person intentionally limits or completely abstains from food intake. There are several forms of fasting, with the most well-known including:

Time-restricted eating / Intermittent fasting (Time-Restricted Eating / Intermittent Fasting) is the simplest method of fasting, involving alternating periods of eating and fasting.

• The 12/12 method (or 14/10): This method alternates 12 hours of eating with 12 hours of fasting. It is a gentler form of intermittent fasting, often recommended for women and beginners so the body can adapt gradually. These protocols align with the natural circadian rhythm and are the safest starting point.

• The 16/8 method: This approach includes 16 hours of fasting and an 8-hour eating window. It is commonly achieved by skipping either breakfast or dinner. It is ideal for beginners after an adaptation period.

Full-day fasting – for example the Eat-Stop-Eat approach, which includes one fasting day per week (e.g., from dinner one day to dinner the next day).

Extended fasts (24–72 hours)

Extended fasts exceed one day and usually include only water, tea, and electrolytes. These fasts may carry higher risks, such as electrolyte imbalances, and should ideally be performed under professional supervision, especially when attempted for the first time.

Why incorporate fasting regularly?

When the body skips its regular food intake, natural processes are activated that have numerous positive effects on the organism. Fasting supports immunity through cellular cleansing (autophagy), reducing inflammation, and regeneration driven by stem cells. It is a powerful way to tap into the body’s innate ability to repair and heal itself.

Regular, well-controlled fasting also increases resistance to viruses and bacteria thanks to the renewal of immune cells and the improvement of their function. This makes it a potentially effective strategy for preventing infectious illnesses.

How does the body respond to a break from food?

Autophagy = the body’s internal cleanup

Fasting is one of the most effective physiological stressors that activate autophagy. Autophagy is a natural cellular process through which the body recycles damaged or unnecessary cellular components. Cells “clean out” old organelles and waste products, supporting their health and function. This process is typically activated after 12–16 hours of fasting and peaks during longer fasts. Autophagy is also linked to reduced oxidative stress, prevention of neurodegenerative diseases, and potential anti-cancer effects. [1]

Anti-inflammatory effects of fasting

In the context of inflammation, it is essential to distinguish between its acute and chronic form. Acute inflammation is a necessary, protective immune response to injury or infection. Chronic, low-grade inflammation, on the other hand, is a key driver of many lifestyle diseases such as heart disease, type 2 diabetes, and neurodegenerative disorders. Research shows that fasting regulates inflammation through several mechanisms. It reduces inflammatory markers such as C-reactive protein (CRP) and interleukin-6 (IL-6), improves gut microbiome composition (which can reduce systemic inflammation), and lowers insulin levels, which itself has pro-inflammatory effects when chronically elevated. [2]

Stem cell regeneration and immune system modulation

As we age, our immune system becomes less efficient. Old, damaged, and dysfunctional immune cells (so-called senescent cells) accumulate, contributing to chronic inflammation and reducing the body's ability to fight infection. Fasting triggers a deep renewal process. During fasting, the body begins breaking down and recycling a large number of old white blood cells, particularly the damaged or senescent ones. During this “cleanup,” levels of the enzyme PKA and the hormone IGF-1 decrease – both of which normally inhibit stem cell activity.

While fasting initiates the cleansing, actual regeneration occurs during the refeeding phase. The influx of nutrients activates the mTOR pathway, essential for protein synthesis and cell growth, stimulating stem cells to rebuild the immune system. Stem cells in the bone marrow act as the “mother hub” of the immune system. They have the ability to continually divide and differentiate into various specialized immune cells needed by the body, repair damaged tissues, and maintain immune balance. The activation of stem cells is therefore a crucial step toward a resilient and healthy immune system.

Ketosis during fasting: a source of energy and a boost for health

During fasting, the body gradually depletes its glucose stores, the primary energy source. Once liver and muscle glycogen are used up, the body begins using fat as fuel. Fatty acids from adipose tissue are broken down in the liver into smaller molecules called ketones. Ketones are not just an alternative fuel – they are also signaling molecules with direct benefits for the immune system. Ketones generate fewer reactive oxygen species (reducing oxidative stress) and have demonstrated anti-inflammatory properties. [3]

For these reasons, the state of ketosis achieved during fasting is considered not only energy-efficient but also a health-promoting mechanism that supports longevity and disease resilience.

How to start fasting

We recommend starting with a simple 12/12 intermittent fasting protocol for one week, then gradually extending the fasting window to 14/10 and eventually to 16/8. It is advisable to give the body around 2 weeks to adapt to each phase, which minimizes initial side effects such as headaches or irritability.

The importance of hydration: During fasting, maintain a sufficient fluid intake, especially clean water, unsweetened teas, or natural mineral waters. Electrolytes also play a key role in proper hydration. As insulin levels decrease, the kidneys excrete more sodium, which can lead to imbalances in other essential electrolytes, such as potassium and magnesium. This imbalance is the main cause of fasting side effects such as headaches, fatigue, and muscle cramps. For fasts longer than 16–18 hours, electrolyte supplementation is recommended, for example by adding a pinch of high-quality sea salt to water or using a specialized electrolyte supplement.

Breaking the fast: The benefits of fasting can be undermined by poor food choices during the refeeding phase. The eating window should be viewed as a “window for repair and nourishment.” It is therefore important to focus on a balanced intake of high-quality protein (for tissue repair), healthy fats (for hormone production and satiety), complex carbohydrates and a wide variety of vegetables for fiber, vitamins, and minerals. After an extended fast (over 24 hours), it is appropriate to start with an easily digestible meal, such as a bone broth.

Specifics of fasting for women

Fasting works somewhat differently for women than for men because the female hormonal system is more sensitive to energy availability. Fasting and overly long fasts in women may affect the balance of sex hormones (estrogen, progesterone), which may lead to irregular menstruation, disrupted ovulation, or reduced fertility. Metabolic stress from fasting can also increase levels of the stress hormone cortisol, which may weaken the immune system. Women’s higher sensitivity to caloric restriction can additionally decrease thyroid hormone production and slow down metabolism. [4] [5]

A static, everyday fasting protocol is therefore not optimal for women. The dynamic nature of the female hormonal cycle requires an equally dynamic approach to fasting, where the protocol is modulated in alignment with the menstrual phases. A suitable approach for women is therefore not simply “intermittent fasting,” but “cyclical intermittent fasting.”

How to time fasting according to the menstrual cycle?

During the menstrual and follicular phases (approximately days 1–14 of the cycle), estrogen levels rise, insulin sensitivity is higher, the body is more resilient to stressors, and it can handle metabolic challenges more effectively. This is therefore the ideal time for women to practice longer fasts, such as 16/8, 18/6, or even a 24-hour fast. However, fasting during the first days of menstruation may be uncomfortable for some women and should be adjusted according to individual feelings.

The ovulatory phase represents the peak of estrogen and luteinizing hormone. According to Mindy Pelz, an American expert on women’s health and fasting and author of Fast Like a Girl, longer fasts should be avoided during the ovulatory phase. Shorter fasts (ideally 13–15 hours) are recommended so that the body has sufficient resources for the metabolism of estrogen and testosterone during the peak of their production. [6]

The luteal phase (approximately days 15–28) is the period when progesterone increases, which slightly reduces insulin sensitivity. For this reason, maintaining stable blood sugar may be more difficult in the second half of the cycle, and cravings may intensify. The body is more sensitive to stress and energy deficits at this time, so fasting is not recommended during this phase.

Who should avoid fasting altogether?

Groups for whom fasting is not suitable include pregnant and breastfeeding women, children and adolescents, individuals with eating disorders, and people who are underweight or malnourished. Fasting also requires medical supervision for individuals with diabetes (especially type 1 or insulin-treated type 2) due to the risk of hypoglycemia, as well as for those with chronic kidney or liver disease, heart conditions, particularly arrhythmias or low blood pressure.

Conclusion

Fasting is not just a wellness trend but a scientifically supported tool that can strengthen the immune system and reduce the risk of infectious diseases. Combining short-term fasting with a diverse diet, physical activity, and sufficient sleep forms an effective strategy to maintain health and resilience.

Key takeaways

• Fasting = intentional limitation or omission of food for a certain period.

• Most common forms: Time-restricted eating / intermittent fasting (12/12, 14/10, 16/8 – alternating eating and fasting periods), full-day fast (Eat-Stop-Eat) – one fasting day per week, extended fasts (24–72 hours)

• Why fasting supports health: It activates autophagy – recycling of damaged cells; has anti-inflammatory effects; supports stem cell regeneration; and triggers ketosis (a state in which the body burns fats into ketones that reduce oxidative stress and support health and longevity).

• How to start fasting: start with 12/12 for one week, gradually extend to 14/10 and 16/8; key factor is hydration – water, unsweetened teas, mineral waters, and electrolyte supplementation.

• Breaking the fast: food should be high quality and balanced; the eating window should be viewed as an opportunity for repair, renewal, and nourishment.

• Specifics for women: women are more sensitive to caloric restriction, which can affect hormonal balance, menstruation, ovulation, and thyroid function. It is important to align fasting with the phases of the menstrual cycle.

• Who should avoid fasting: pregnant and breastfeeding women, children and adolescents, individuals with eating disorders, people who are underweight or malnourished. People with diabetes, chronic kidney, liver or heart disease, or low blood pressure should consult a physician before fasting.

Sources:

[1] Nicolai, C. J., and David H. Raulet. "Roles of Natural Killer Cells in Immunity to Cancer, and Applications to Cancer Immunotherapy." Nature Reviews Cancer, vol. 22, no. 5, 2022, pp. 268–285. 

https://www.cell.com/immunity/fulltext/S1074-7613(24)00275-9

[2] Hein ZM, Arbain MFF, Kumar S, Mehat MZ, Hamid HA, Che Ramli MD, Che Mohd Nassir CMN. Intermittent Fasting as a Neuroprotective Strategy: Gut-Brain Axis Modulation and Metabolic Reprogramming in Neurodegenerative Disorders. Nutrients. 2025 Jul 9;17(14):2266. doi: 10.3390/nu17142266. PMID: 40732891; PMCID: PMC12298811.

[3] Youm YH, Nguyen KY, Grant RW, Goldberg EL, Bodogai M, Kim D, D'Agostino D, Planavsky N, Lupfer C, Kanneganti TD, Kang S, Horvath TL, Fahmy TM, Crawford PA, Biragyn A, Alnemri E, Dixit VD. The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome-mediated inflammatory disease. Nat Med. 2015 Mar;21(3):263-9. doi: 10.1038/nm.3804. Epub 2015 Feb 16. PMID: 25686106; PMCID: PMC4352123.

[4] Alvero R, Kimzey L, Sebring N, Reynolds J, Loughran M, Nieman L, Olson BR. Effects of fasting on neuroendocrine function and follicle development in lean women. J Clin Endocrinol Metab. 1998 Jan;83(1):76-80. doi: 10.1210/jcem.83.1.4512. PMID: 9435419.

[5] Matzen LE, Kvetny J. The influence of caloric deprivation and food composition on TSH, thyroid hormones and nuclear binding of T3 in mononuclear blood cells in obese women. Metabolism. 1989 Jun;38(6):555-61. doi: 10.1016/0026-0495(89)90216-3. PMID: 2725295.

[6] Pelz, Mindy. Fast Like a Girl: A Woman’s Guide to Reclaiming Conscious Femininity, Sexual Energy, Intuition, Libido, and Fertility. Harmony Books, 2021.