Guest article by our nutrition expert Dr. Dorothea Portius
Fasting is one of the oldest therapeutic methods and has deep roots in medical, religious and cultural practices [1]Hippocrates already praised fasting as a healing remedy, and in many cultures – from Ramadan to ritual fasting in Christianity – it has been used as a spiritual and health practice for thousands of years. how does Fast on the body, and what biochemical processes make it a potent tool for health and regeneration?
What is fasting?
Fasting describes the conscious abstinence from food or, depending on the fasting protocol, from certain foods or nutrients for a defined period of time. This abstinence can range from a few hours to several days and includes various types of fasting, such as
- “Natural” nighttime fastingFasting period: The period between the last meal of the day and breakfast the next morning. During this natural fasting phase, which typically lasts 8–12 hours, regenerative processes are already taking place in the body (depending on health and the composition of the evening meal).
- Intermittent fasting (intermittent fasting): Here, phases of fasting and eating alternate in a defined rhythm, e.g., 16 hours of fasting and 8 hours of eating (16:8).
- therapeutic fasting: Fasting periods that last from 24 hours to several days and are usually carried out under medical supervision, such as the Buchinger therapeutic fast.
Fasting is by no means a passive state, but an active, highly dynamic process, in which the body activates specific mechanisms to adapt to the temporary deprivation of energy. These processes ensure that the organism functions optimally even with a restricted nutrient supply. The temporary deprivation of food signals the body to use resources efficiently and initiate regeneration mechanismsHowever, this “fasting stress”, when carried out adequately and in accordance with one’s own needs, differs from chronic stresswhich can harm the body because it is temporary and promotes adaptive processes [2, 3].
Fasting promotes these adaptive processes
Energy metabolism and metabolic switching
In the first 6-8 hours, the body draws on the glycogen reserves (carbohydrate stores) stored in the liver to produce glucose (Sugar). After about 12-24 hours, when the glycogen stores are depleted, the body begins to convert fatty acids from the fat deposits in the liver into ketone bodiesKetone bodies serve as an alternative energy source, especially for the brain. Better Blood sugar levels are also important in the fight against Insulin resistance.
Autophagy – Cellular cleaning mechanism and regeneration
Fasting induces autophagy, a process by which old and damaged cellular components (“cellular junk”) are broken down and recycled.This mechanism protects cells from oxidative stress, reduces Inflammations and supports tissue regeneration and ensures that cells maintain their normal functions.These mechanisms and autophagic processes are already triggered during nighttime fasting [4, 5].
Increased mitochondrial efficiency
Fasting poses a physiological challenge for the Mitochondria – the “power plants of the cell” – and forces them to optimize their energy production. This leads to increased cellular resistance to oxidative stress and promotes metabolic flexibilityThis term describes the organism's ability to adapt to changing energy sources—carbohydrates or fats. High metabolic flexibility is considered an indicator of low cellular aging, while smooth transition between energy sources is associated with slowed cellular aging. [6].
Hormonal adjustments
The hormonal adjustments during fasting play a central role in metabolic changes at the cellular level. The body responds to the energy deficiency through finely tuned hormonal regulation, which includes both short-term and long-term adaptation processes.
During fasting insulin levels decrease, which can improve insulin sensitivity and reduce the risk of insulin resistance and type 2 diabetesAt the same time, the release of glucagon, the antagonist of insulin, increases. Glucagon mobilizes stored energy reserves and stimulates glucose production in the liver. Furthermore, the increased release of growth hormones such as human growth hormone (HGH) promotes lipolysis (fat burning) and contributes to the maintenance of muscle mass by limiting catabolic processes. [7]. Get more sugar tips in our article about Jessie Inchauspé - also known as Glucose Goddess.
However, the body also releases increased levels of stress hormones such as adrenaline and noradrenaline, because the lack of energy activates the sympathetic nervous system and puts the organism into an “alarm mode”This leads to a short-term increase in alertness, increased lipolysis, and increased energy supply to vital organs, especially the brain. However, this stress reaction is primarily limited to acute phases and serves to adapt to the lack of energy, not to regenerate.
Fasting can be particularly beneficial during periods of high physical or mental stress and cause more stress than health benefits for certain groups of peopleThese include women in the luteal phase, competitive athletes, pregnant women, adolescents, and people with acute infections. In individuals already under elevated physiological or psychological stress, increased activation of the sympathetic nervous system can place additional strain on the organism, weakening or even counteracting the potential health benefits of fasting.
Anti-inflammatory effects
Fasting exerts its anti-inflammatory effect through several interconnected mechanisms[8]. Temporary food deprivation reduces the production of pro-inflammatory cytokines such as TNF-α and IL-6, while anti-inflammatory mediators such as IL-10 are enhanced.
Fasting reduces oxidative stress by reducing the formation of reactive oxygen species (ROS) and antioxidant protection systems such as superoxide dismutase (SOD) and glutathione peroxidase are activated. Through more efficient mitochondrial energy production, as described above, oxidative damage to cell structures is reduced. [9]. You can learn more about glutathione in the article about GlyNAC.
In addition, fasting modulates the intestinal microbiome and thus promotes the production of anti-inflammatory short-chain fatty acids such as butyrate [5]These short-chain fatty acids not only strengthen the intestinal barrier but also have a systemic effect on several organ systems. You can read more about butyrate in the article on QBIOTIC read.
Conditions for which fasting offers benefits
Metabolic diseases
Type 2 diabetes: Fast improves insulin sensitivity and reduces fasting blood sugarStudies show that intermittent fasting can significantly reduce HbA1c levels [10, 11].
Danger: Patients receiving insulin or sulfonylurea therapy should only fast under medical supervision because of the risk of hypoglycemia.
Obesity: Fasting can reduce body weight and especially visceral fat. This has a particularly positive effect on chronic inflammatory processes. [5, 12] or Inflammaging.
Cardiovascular diseases
Fasting can lower LDL cholesterol and triglycerides, with less impact on HDL levels. However, it improves the LDL-to-HDL ratio, which can counteract the development of oxidative stress and promote endothelial cell function, crucial for vascular health. [13]. Blood lipid levels Keeping it within limits is a very important issue for greater longevity.
Neurodegenerative diseases
Fasting increases the production of neurotrophic factor (BDNF), which promotes the growth of new nerve cells and protects the brain from degeneration. There is evidence that fasting, especially intermittent fasting, can reduce the risk of Alzheimer's and Parkinson's diseases. [14].
Cancer prevention and therapy
Tumor cells exhibit a fundamentally altered metabolism compared to healthy cells. They predominantly metabolize glucose at a high rate, even under anaerobic conditions – a phenomenon known as Warburg effect This increased glycolysis makes them particularly dependent on a constant glucose supply and insulin-mediated growth signals.
Fasting reduces insulin secretion and the activation of growth-promoting signaling pathways such as mTOR, which can inhibit tumor-specific metabolic processes and slow the growth of some tumor types. Studies suggest that fasting in combination with chemotherapy improves treatment efficacy and reduces side effects. [15]
Diseases where caution is required
Hyperuricemia and gout
Fasting promotes the cellular degradation and renewal process (autophagy), which increases the recycling of cellular components. This releases purines, among other substances, whose degradation leads to the formation of uric acid. As a result, uric acid levels can rise during fasting, increasing the risk of gout attacks in predisposed individuals. Learn more about autophagy in the article on Spermidine.
Recommendation: Gout patients should only fast in consultation with a doctor or nutritionist. A cautious approach with shorter fasting periods (e.g., 12–14 hours) and adequate fluid intake to promote uric acid excretion are essential.
Eating disorders and underweight
Fasting can lead to an additional calorie deficit in patients and individuals who are underweight, exacerbating the existing deficiency and further exacerbating catabolic metabolism. Furthermore, hormonal adaptation to the energy deficiency, such as increased cortisol secretion, can increase the risk of further health complications such as bone density loss, cardiac arrhythmias, and delayed metabolic recovery.
In individuals with eating disorders such as anorexia nervosa, fasting can also reinforce restrictive eating patterns and further promote pathological behavior toward food.
Recommendation: People with underweight, eating disorders or a history of such disorders should generally avoid fasting and ensure a balanced, regular food intake, ideally under medical or nutritional supervision.
Pregnancy and breastfeeding
Fasting is not recommended during pregnancy and breastfeeding, as a continuous supply of energy and nutrients is crucial for the health of mother and child during these phases. The increased calorie and nutrient requirements support the growth and development of the fetus as well as milk productionA calorie deficit caused by fasting could cause deficiencies that can increase the risk of complications during pregnancy and lead to inadequate nutrient supply for the infant. Furthermore, fasting can negatively affect maternal metabolism and hormonal balance, which could impact the mother's physical and mental health as well as the development of the child.
Recommendation: Instead of fasting, you should focus on a balanced and nutrient-rich diet to meet the special needs of these phases of life. If you are unsure, consulting a doctor or nutritionist can be helpful.
When does fasting become a positive signal?
For fasting to have a health-promoting effect, certain conditions must be met:
Sufficient adjustment time
The body needs time to get used to fasting – especially when it comes to longer fasting periods or new fasting protocols.Fasting that is too abrupt or extreme can overtax the body, which can result in symptoms such as headaches, weakness or concentration problems.
Individual customization
Fasting is not a "one-size-fits-all" approach. Factors such as age, gender, metabolism, hormonal status, and existing medical conditions influence how well the body responds to fasting. Women in the premenopausal phase or people with metabolic disorders often require individually adapted fasting periods to avoid negative effects such as hormonal imbalances.
Adequate nutrient supply during meal times
Between fasting periods, it is essential to provide the body with sufficient nutrients. A lack of essential Vitamins, minerals or calories can reverse the positive effects of fasting and lead to fatigue, muscle loss or weakened immune function.
Appropriate duration and intensity
- Short fasting (12–16 hours): Promotes regeneration and activates processes such as ketosis and autophagy without placing too much strain on the body.
- Longer fasting (24–72 hours): Can trigger deeper repair processes, but requires careful planning and medical monitoring to avoid overload or nutrient deficiencies.
- Chronic fasting or excessive calorie restriction: Can put the body into a state of chronic stress, disrupt hormone regulation, and increase the risk of health problems such as loss of muscle mass or disruption of the menstrual cycle.
Conclusion: The art of fasting correctly
Fasting is a natural and scientifically based method for promoting health. It can activate regenerative processes, optimize metabolism and develop anti-inflammatory and cell-protective effects. The following applies: Even short fasting phases, such as fasting at night, provide positive stimuli, and an extension of the fasting interval (primarily by eating the evening meal earlier) can increase the health benefits.
However, fasting is not a universally suitable concept, but requires individual adaptationDuring certain life stages, such as pregnancy, breastfeeding, or adolescence, as well as in certain medical conditions such as gout or eating disorders, fasting can potentially do more harm than good. Too frequent or too intense food restriction can also reverse the beneficial stimulus into detrimental metabolic stress.
With growing scientific evidence, fasting is becoming established not only as a preventative measure, but also increasingly as a complementary therapeutic option. A mindful approach that takes personal requirements into account is crucial to maximize the health benefits and minimize potential risks.
