Intermittent fasting, also known as intermittent fasting, describes a nutritional method in which eating times and breaks are consciously structured. In contrast to constant calorie reduction, intermittent fasting involves alternating phases of food intake and fasting windows. The aim is to teach the body to use energy more efficiently, boost the metabolism and increase the flexibility between burning fat and carbohydrates. Historically, fasting is a natural part of human life, as our ancestors did not always have access to food. Today, it serves as a concept to enrich the modern lifestyle with targeted food breaks. In the following article, we show you which fasting methods are available, how to carry out intermittent fasting safely and how to optimize your own fasting plan.
Unlike starvation, intermittent fasting does not mean torturing yourself over a long period of time[10]. Rather, phases of eating and fasting alternate so that the body has time to process nutrients without being constantly occupied with digestion. Time-restricted eating, also known as time restriction, can mean, for example, eating within a time window of eight hours and fasting for 16 hours (16/8 diet). Other forms are the 14/10 variant or the 5:2 diet, in which you eat normally on five days and greatly reduce your calorie intake on two days. Another form is Alternate Day Fasting, in which normal days alternate with very low-calorie fasting days. These methods rely on regular breaks from eating and differ from long-term fasting, which involves several days without solid food.
The most popular fasting methods include the 16/8 diet and the 14/10 method. These involve eating between 10 am and 6 pm or 9 am and 7 pm, for example. These forms of time restriction are particularly suitable for everyday life, as they are easy to combine with work and family life. The 5:2 diet requires a significant reduction in calories (typically 500 kcal) on two days, while a balanced, calorie-conscious diet is followed on the other days. Alternate Day Fasting aims to eat only one small meal every other day and eat normally on the other days. With all methods, it is important to choose high-quality foods, drink plenty of water and listen to your body. If you are active in sports, you should plan your fasting periods so that training sessions do not fall during the strenuous phases.
Numerous studies have investigated the effects of intermittent fasting on body weight and metabolism. In a randomized study with people suffering from obesity and type 2 diabetes, both the 16/8 and 14/10 methods, when used three days a week for three months, led to a significantly higher percentage weight loss (-4.02 % and -3.15 % respectively) than the control group (-0.55 %)[1]. In addition, fasting blood glucose, HbA1c levels and lipid profiles improved, indicating better insulin sensitivity. Another randomized study compared Alternate Day Fasting with daily calorie restriction and found that weight loss was similar after six and twelve months (about 6% of initial weight in each case). There were no significant differences in blood pressure, cholesterol or insulin resistance between the groups[2]. These results show that intermittent fasting can help with weight loss and improve metabolism. However, it is not necessarily more effective than conventional calorie restriction. Many of the benefits observed are probably due to the calorie deficit and depend on individual implementation.
Reviews report that intermittent fasting resulted in significant weight loss of 3.2% to 8% in 75% of the studies examined and in some cases improved insulin concentrations and inflammatory markers. In the same analysis, less than 15% of participants reported adverse side effects such as feeling cold, irritability, low energy or hunger. A notable benefit was the improvement in mood and general well-being for many people. However, intermittent fasting was no more effective than continuous energy restriction in several studies. This indicates that ultimately total energy intake and nutritional quality are crucial[3][9].
Intermittent fasting promotes metabolic flexibility. During eating phases, the body uses carbohydrates as an energy source; during fasting phases, it draws on fat reserves and produces ketone bodies. This change enables the metabolism to adapt better. It is assumed that fasting activates autophagy, the intracellular recycling process. This allows damaged cell components to be broken down and renewed, which could contribute to cell renewal in the long term. So far, these processes have mainly been observed in animal models; their relevance in humans has not yet been fully proven. Therefore, the links between autophagy and intermittent fasting have not yet been confirmed by the EFSA; further studies are required. Some studies suggest that fasting can reduce inflammation, which could be helpful in chronic diseases such as metabolic syndrome or cardiovascular disease. But again, official health claims are lacking and caution is advised.
Improved insulin sensitivity is one of the most discussed arguments for intermittent fasting. When the body is deprived of sugar over longer periods, insulin levels fall. This makes it easier to burn fat and can keep blood sugar levels stable. The study mentioned above showed an improvement in fasting blood glucose and HbA1c levels. However, it should be emphasized that these results are from a limited number of subjects and further research is needed to confirm long-term effects. There is evidence that withholding meals could boost metabolism and increase lifespan. In animal experiments, an increase in lifespan was observed when mice fasted and consumed fewer calories[5]. However, there is a lack of reliable long-term studies in humans, so these results should be interpreted with caution. People with existing illnesses should only start fasting in consultation with medical staff.
Many people fear that fasting and muscle building do not go together. In fact, some studies show that intermittent fasting in combination with strength training helps to maintain muscle mass. It is crucial that enough protein, healthy fats and complex carbohydrates are consumed during the eating windows. Those who combine fasting and sport should ideally adapt training sessions to the eating window so that the body has sufficient energy available. Another concept is to combine intermittent fasting with a ketogenic diet(keto and fasting). As both methods lower insulin levels and promote fat burning, together they can support the metabolism. However, this combination is not suitable for everyone, especially people with pre-existing conditions or pregnancy. Listen to your body's signals and talk to professionals before starting special diets or fasting programs.
Intermittent fasting not only affects the body, but also the brain. The limited food intake can increase the production of neurotrophins such as brain-derived neurotrophic factor (BDNF), which is important for the formation of new nerve cells. Some studies suggest that fasting may improve concentration and slow down neurodegenerative processes[6]. In the aforementioned review, many participants reported a better mood and less fatigue. Nevertheless, short-term side effects such as headaches, irritability or reduced energy can occur. A balanced fasting plan should therefore not only take into account physical goals, but also mental health.
Safety is the top priority with intermittent fasting. Not everyone should fast: pregnant and breastfeeding women, children, people who are underweight, people with eating disorders or chronic illnesses should refrain from fasting diets or only do them under medical supervision. A good fasting plan involves a gradual approach. Start with 12 hours of fasting and slowly extend the period. Make sure you drink enough water and unsweetened tea to maintain your fluid balance. During the eating phases, you should choose wholesome foods that are rich in fiber, protein and micronutrients. If you want to try long-term fasting (several days), you should only do so after consulting a specialist. Keep a diary to monitor your well-being, sleep and energy levels. Side effects such as dizziness, extreme tiredness or severe hunger are warning signs that the fasting plan needs to be adjusted.
The point at which you break the fast(breaking the fast) is just as important as the fast itself. A typical mistake is to reward yourself with large amounts of high-calorie or processed food after fasting. It is better to end the fasting phase with easily digestible foods such as soups, salads or a detox smoothie. This is easy on the digestive tract and provides the body with important nutrients. This can be followed by a balanced main meal. The so-called "fasting window" should not end too late in the evening so that the body has enough time to digest and sleep is not affected. If you feel hungry late in the evening, you can satisfy your appetite with a small portion of protein and vegetables without putting too much strain on your blood sugar. For people with a pronounced chronotype or changing working hours, fasting periods can be adapted to individual needs.
Another aspect of intermittent fasting that has been discussed is its effect on the immune system and inflammatory processes. Some research results suggest that controlled fasting can reduce the level of pro-inflammatory cytokines and strengthen antioxidant systems. This could result in a supportive effect of fasting against inflammation. At the same time, the body can form new immune cells through periods of fasting, a process known as cell renewal. These hypotheses are being intensively investigated; however, there are currently no approved health claims. Therefore, claims about fasting and curing disease should be avoided. If you have inflammatory diseases, always check with a doctor whether and how fasting makes sense.
Many people find intermittent fasting socially challenging. Appointments, business lunches or family celebrations often fall during fasting windows. This is where planning and openness can help: explaining your fasting plan to others will ensure understanding and support. Apps that function as fasting apps can plan meals, remind you to take your next drinking break and document your progress. Some programs have social components so that you can exchange ideas with like-minded people. Another tip is to bridge meal breaks with gentle physical activity such as walking. If you are aiming for metabolic flexibility, make sure you have a high quality of life and plan in enough sleep, exercise and social contact.
Animal studies show that calorie restriction and intermittent fasting can extend lifespan. Scientists explain this by reduced activity of the mTOR signaling pathway and increased autophagy. Initial observations in humans suggest that controlled energy restriction may be associated with lower morbidity, but the data is still insufficient. Therefore, statements such as "fasting helps longevity" should always be put into perspective. The links between intermittent fasting and longevity have not yet been confirmed by the EFSA; further studies are required. Excessive fasting intervals can lead to nutrient deficiencies. Long-term health is based on a balanced diet, regular exercise, sufficient sleep and maintaining relationships. Intermittent fasting can be a building block, but should not be seen as a miracle cure.
Many people use intermittent fasting as part of a detox cure or liver cleanse. In such cases, periods of fasting are combined with the consumption of fresh juices, detox teas or detox smoothies. This can relieve the body and promote the flow of bile. However, experts point out that excessive detoxification has no recognized medical basis and has no approved health claims. Liver supplements or herbal preparations should only be taken after consultation with specialists. It is more important to eat naturally, drink enough and avoid processed foods. A healthy liver detoxifies the body efficiently - with or without fasting.
Intermittent fasting can be integrated into everyday life if you adapt the method to your own rhythm of life. For working people, it can be helpful to set the meal window around lunchtime so that you can have lunch with colleagues. If you work shifts, you should be flexible with your fasting times and shorten the fasting window if necessary. It is important that your body gets enough nutrients. Plan your meals in advance to avoid spontaneous unhealthy snacks. If you exercise regularly, you can fit your physical activity into the eating window so that your energy intake covers your needs. Finally, it is helpful to exchange ideas with like-minded people: Many people share their fasting tips and experiences on forums or social networks. The aim is to develop a sustainable lifestyle that is good for body and mind.
Intermittent fasting is a versatile method that can help to reduce weight, improve metabolism and possibly increase quality of life. The best-known fasting methods include 16/8 and 14/10 time restriction, the 5:2 diet and Alternate Day Fasting. Scientific studies show that these approaches can lead to weight loss and improved metabolic parameters, but are not necessarily superior to continuous calorie reduction. Individual tolerance varies; some people report more energy, mental clarity and better sleep, while others initially feel hungry or irritable. If you want to try intermittent fasting, you should start with small steps, drink enough, focus on nutritious foods and seek medical advice if you have any health problems. There is no miracle diet; what counts in the long term is a balanced diet, regular exercise and a mindful lifestyle. Intermittent fasting can be a valuable building block to relieve the body, promote metabolic flexibility and be more conscious about food. Follow the tips, listen to your body and don't overstrain yourself - then intermittent fasting can become a healthy companion.
Meal breaks, digestion and gut health
A regular break between meals gives the digestive system the rest it needs to fully process nutrients and dispose of waste. When the body is not constantly busy digesting, it can focus on repair processes, which is interpreted as "cleansing". During the breaks, less insulin is released, the liver gets recovery time and the intestines have the opportunity to regenerate. Some people report that intermittent fasting gives them less bloating and a more stable gut feeling. The role of the microbiome - the beneficial microorganisms in the gut - is particularly interesting here. During fasting, metabolic products change and intestinal bacteria work more efficiently. To support the digestive tract, fermented foods such as sauerkraut, kefir or kimchi are suitable during meal windows. These probiotic foods promote healthy intestinal flora and provide valuable enzymes. The links between intermittent fasting, the microbiome and healthy digestion have not yet been confirmed by the EFSA; further studies are required.
Fasting, stress and sleep hygiene
Fasting not only changes your diet, but also your stress levels and sleep. Some people who are fasting experience increased tension during the initial period because they no longer have their usual snacks. It can help to consciously plan breaks for relaxation. Techniques such as deep breathing, meditation or gentle music therapy can help to counterbalance the lack of food. A calming aromatherapy scent of lavender or bergamot can also increase your sense of well-being. A short walk in the forest - "forest bathing" - also supports stress management, as nature has been proven to promote a calming atmosphere. Sleep hygiene is also important. A fixed evening ritual, dimmed lights and abstaining from heavy meals shortly before sleep improve sleep. Some fasting people report that their sleep stabilizes after the adjustment phase because blood sugar and insulin levels are more balanced. Nevertheless, sleep problems should be taken seriously: If sleep is persistently disturbed, the body may need more energy or a different fasting method.
Everyday exercise and thermogenesis
To maximize the benefits of fasting, it is worth incorporating daily exercise into your plan. This concept is also called NEAT ("Non-Exercise Activity Thermogenesis") and describes the energy that is burned during simple activities such as walking, climbing stairs or household chores. If you consciously exercise during fasting windows, you can increase your calorie consumption without having to complete intensive sports programs. Studies suggest that regular exercise boosts the metabolism, improves insulin sensitivity and lifts the mood. It also helps to lower blood pressure and cholesterol levels. Integrating exercise is not about overtaxing the body. Small routines such as talking on the phone while walking, taking a short walk during your lunch break or stretching at work can make a difference. When combined with intermittent fasting, these activities enhance the fat-burning effect and contribute to holistic health in the workplace.
Intermittent fasting in different phases of life
The optimal fasting method depends on age, health and life circumstances. Younger people and healthy adults can often tolerate longer fasting intervals and benefit from increased metabolic activity. In older people, however, fasting for too long can lead to muscle loss because the body tends to use muscles as a source of energy. Senior citizens should therefore choose shorter fasting periods and pay particular attention to sufficient protein intake. Pregnant or breastfeeding women and people with chronic illnesses or who are underweight should only fast after consulting a doctor or refrain from fasting altogether. The individual chronotype also plays a role: those who are "owls" can plan their eating window later in the day, while "larks" tend to close their fasting window in the early evening. A personalized approach takes these differences into account and ensures that intermittent fasting is supportive and not stressful.
Myths and common mistakes
There are many myths surrounding intermittent fasting. One common misconception is: "If I fast, I can eat whatever I want at mealtimes." This idea often leads to calorie bombs and therefore unwanted weight gain. Another assumption is that fasting has the same effect on everyone. In truth, everyone's metabolism reacts differently; some lose weight quickly, others more slowly. Some people believe that fasting is a miracle cure that works without a conscious lifestyle. However, without a balanced diet, exercise and rest, there will be no success. Another mistake is to abruptly extend the fasting window. If you go from 12 hours to 20 hours, you risk circulatory problems and food cravings. It is better to proceed gradually, drink enough and consult an expert if you have any complaints. Intermittent fasting is a method, not a panacea - and must be adapted to suit the individual.
Tips for getting started
If you want to try intermittent fasting, you should set yourself a clear plan. At the beginning, it is advisable to keep a diary to document meals, mood and physical sensations. This will help you to recognize patterns and make adjustments. Plan your meals in advance - especially if you are working. A prepared snack of nuts, fruit or vegetables will prevent you from reaching for processed foods. Apps can help with time management by reminding you of meal and fasting times. It is also advisable not to schedule fasting times on particularly stressful days, but on quieter periods. Build in breaks for drinking: Unsweetened tea and water keep your circulation stable. If you notice problems with your circulation or concentration, you can temporarily shorten the fasting window. Start with manageable periods such as 12/12 or 14/10 and only extend them once your body has become accustomed to them.
Nutrition during the eating window
The quality of the food you eat has a major impact on how fasting affects your body. High-fiber vegetables, fruit and whole grain products should dominate during the eating window, supplemented by high-quality proteins and healthy fats. Nuts, pulses and fish provide essential amino acids and omega-3 fatty acids, which support the cardiovascular system. Fermented foods such as yogurt, kefir and kimchi strengthen the microbiome. Bitter substances from herbs such as milk thistle or artichoke can promote bile flow; however, the effects have not been confirmed by EFSA health claims, which is why these claims must be accompanied by a disclaimer: The links between bitter substances and liver health are not currently confirmed by EFSA; further studies required. Avoid highly processed foods, sugar and trans fats. Be careful not to eat too large meals; several smaller portions stabilize blood sugar levels and prevent cravings.
Community and motivation
The social aspect has a significant impact on the success of intermittent fasting. It is easier to change habits when friends or family members support you. Share your plans openly with your community to promote understanding. Shared social activities such as going for a walk, cooking or sharing meals within the eating window can strengthen the group feeling. Online forums and local groups offer platforms for sharing experiences and tips. Sharing successes and challenges keeps you motivated and gives you fresh impetus. At the same time, beware of unrealistic expectations on social media. Every body reacts differently, so don't constantly compare yourself with others. The feeling of community, team spirit and empathy supports the mental process and promotes long-term change.
Scientific perspectives
Current studies show that intermittent fasting leads to weight loss and improved metabolism in many people. However, the long-term effects have not yet been fully researched. Most studies cover a few months and small numbers of participants, making it difficult to draw general conclusions. Further studies need to investigate the influence on cardiovascular diseases, neurodegenerative diseases and hormone balance. People react individually to fasting, depending on genetics, lifestyle and initial weight. Scientists are working to better understand mechanisms such as autophagy, mTOR signaling pathways and the influence on the microbiome. Until reliable data is available, fasting concepts should be seen as a supplement to proven health strategies - not a replacement.
Fasting in harmony with the internal clock
Chrononutrition, i.e. the interplay between nutrition and circadian rhythm, plays an increasingly important role in intermittent fasting. Our body follows a daily rhythm that regulates sleep, hormones and metabolic processes. Studies suggest that people who eat their meals earlier in the day are better able to deal with glucose. If the eating window falls in the morning and early afternoon, this can stabilize blood sugar levels and optimize metabolism. This does not mean that everyone has to eat breakfast, but that you should adapt your meals to your own biorhythm. If you don't feel hungry until after 10 a.m., you can postpone breakfast and still enjoy the benefits of a time restriction. It is important that meal times do not work permanently against your internal clock - regular times promote both digestion and sleep.
Gut health and fermented friends
A healthy gut contributes significantly to well-being. There appears to be an interaction between fasting and gut health: During periods of fasting, the composition of intestinal bacteria changes and certain species are better able to multiply. Fermented foods provide live cultures that diversify the microbiome. Probiotic foods such as sauerkraut, kombucha or miso support digestion and can be consumed in small portions during meal windows. In addition, fiber from vegetables and whole grains promote the growth of beneficial bacteria. Some people also use fermentation at home to produce inexpensive and fresh probiotics. It is important to note that the health claims for fermented foods - for example to improve mood or reduce stress - have not yet been confirmed by EFSA; further clinical studies are needed. Nevertheless, the conscious use of such foods can be part of a balanced dietary strategy.
Heart health and fasting
Cardiovascular disease is a leading cause of morbidity and mortality worldwide. Some studies suggest that intermittent fasting can have positive effects on blood pressure, cholesterol and inflammatory markers. In a pilot study with metabolic syndrome, participants' systolic blood pressure and LDL cholesterol decreased significantly during a ten-hour eating window without any change in drug therapy[8]. Although the results are promising, they are based on small numbers of participants. Therefore, statements on the prevention of heart disease should be formulated with caution and always include the caveat: The links between intermittent fasting and heart health are not currently confirmed by EFSA; further studies required. People with high blood pressure or heart problems should consult a doctor before fasting. A heart-healthy diet, regular exercise and stress reduction remain the basis for a strong heart.
Intermittent fasting and modern media
There are countless success stories about intermittent fasting circulating on social media. Photos of rapid weight loss and strict diet plans can create pressure and distort your own perception. It is important to view such content critically and not to compare yourself with unattainable ideals. Reliable information comes from scientific studies and specialist literature and not from influencers who generalize their personal experience. Use media wisely by informing yourself about how to do it properly and sharing information in supportive communities. Be careful to avoid stress through constant self-promotion and set clear limits for online time. Intermittent fasting should be an enrichment, not an additional stress factor.
Autophagy, mTOR and cell renewal
A central theme in intermittent fasting is autophagy, i.e. the recycling of cellular components. During fasting, energy reserves become scarce so that the body breaks down damaged cell components and recycles them into new building blocks. At the same time, fasting inhibits the mTOR signaling pathway, which is associated with cell growth and ageing processes. In animal models, this combination extended lifespan, but in humans there is only evidence from observational studies so far. To boost autophagy, short periods of fasting such as 16/8, combined with regular exercise and sufficient sleep, are often sufficient. However, overemphasizing these mechanisms as a rejuvenation cure is not permissible. Again, the links between autophagy and intermittent fasting have not yet been confirmed by the EFSA; further studies are required.
Concentration and mental clarity
Many people report that they feel more mentally alert during intermittent fasting. This could be due to the fact that the body produces ketone bodies during periods of fasting, which provide a stable source of energy for the brain. Some animal studies show that fasting increases the production of brain-derived neurotrophic factor (BDNF), which is responsible for the formation of new synapses. People report better concentration, increased creativity and a feeling of mental lightness. Nevertheless, there are also critical voices: If calorie restrictions are severe, performance can drop in the short term, especially if sleep or fluid intake is insufficient. Therefore, learning or work phases should be strategically placed in the eating windows so that the brain has enough glucose available. As always, every body reacts differently and long-term effects still need to be studied in more detail. So far, no official health claims on mental improvements through fasting have been confirmed.
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