Figure 1: Intermittent fasting has experienced a real hype in recent years. Besides weight reduction, “intermittent fasting” can, among other things, have a positive effect on blood sugar levels and cardiovascular health.
In intermittent fasting, the timing and frequency of food intake are more important than the type of diet. Although the goal is often long-term weight loss, intermittent fasting is also attributed additional potential health benefits. In this article we provide an overview of the most popular forms of intermittent fasting and take a look at the current research on the topic. Finally, you will receive seven practical tips designed to make it easier for you to get started with intermittent fasting.
Intermittent fasting: a long-term lifestyle change rather than a crash diet
Figure 2: Intermittent fasting follows a long-term approach. Rather than a short-term, highly restrictive diet, intermittent fasting is about a sustainable adjustment of lifestyle and eating habits.
Fasting is an age-old practice: Hippocrates is said to have recommended it as a remedy, and fasting rituals are also firmly rooted in the major world religions. In Christianity, Lent before Easter recalls Jesus’ 40-day fast in the desert and serves for inward reflection and penance. Muslims refrain from food and drink from dawn to sunset during the holy month of Ramadan. This is also, in a broader sense, a form of intermittent fasting, since fixed time windows for eating and abstaining from food apply.
For some time now, “intermittent fasting” has been widely discussed, mainly because of the health benefits attributed to it. It is said to contribute to sustainable weight loss by favouring a long-term change in eating habits rather than short-term, restrictive diets. The day is divided into eating and fasting periods. During fasting periods no calories are consumed – only calorie-free drinks such as water, tea or unsweetened coffee without milk are permitted. Unlike classic diets, intermittent fasting does not prescribe a maximum daily calorie intake.
Possible benefits of intermittent fasting
The effects of intermittent fasting on the human body are currently being intensively researched. Depending on the chosen method, different effects are possible. As explained in the following section, however, these are so far mostly hypotheses, because the evidence on the effects of intermittent fasting in humans remains inconsistent. Many people practise intermittent fasting in the expectation of achieving one or more of the following effects:
- weight loss
- preventive effects for chronic diseases (e.g. diabetes mellitus, neurological conditions, cardiovascular diseases)
- potential life-extending effects
- strengthening of the immune system
- optimisation of metabolism (e.g. more stable blood sugar, improved insulin sensitivity)
- increased resilience to oxidative stress
- anti-inflammatory effects
In principle, many of the effects mentioned during fasting can be attributed to the process of autophagy. The term “autophagy” literally means “self-eating” and describes the natural cellular cleansing and recycling process, in which old and damaged cellular components are broken down and the cell partially “renews” itself. Autophagy is particularly active when insulin levels are low – as is the case during fasting periods. Possible benefits of autophagy, which to date have only been demonstrated in animal studies, include cellular rejuvenation, protection against neurodegenerative diseases and slowed ageing processes.
Insulin secretion and metabolic flexibility also play an important role in intermittent fasting. Eating less often means the body secretes insulin less frequently, which in the long term can improve insulin sensitivity and resistance. Fasting also trains the body to switch more quickly and flexibly between burning sugar and fat, which is often associated with a more stable energy level and less cravings.
Are the effects of intermittent fasting scientifically proven?
Figure 3: Some studies suggest that intermittent fasting may be superior to a conventional diet in terms of reducing body fat.
As already indicated, there are currently only relatively few human studies dealing with the effects of intermittent fasting. There are several reasons for this. For one, autophagy in humans is difficult to measure. While in animal studies relevant tissues – for example from the brain or liver – can be examined directly, biopsies would be required for this in humans. These would not only be invasive, but also ethically problematic. In addition, meaningful long-term studies involve significant practical and financial challenges. To make reliable statements about the possible effects of intermittent fasting on longevity, diet, physical activity and sleep behaviour of thousands of participants would have to be controlled for decades. Such a study design would be extremely complex and costly.
Against this background, it is hardly surprising that the few clinical studies available produce inconsistent results. For example, a study with 25 healthy young men suggests that intermittent fasting may have long-term anti-inflammatory effects and promote autophagy. Other studies report positive effects in people with diabetes mellitus (type 1 and type 2) and with regard to the prevention of cardiovascular diseases.
As many people practise intermittent fasting with the goal of losing body weight, the evidence in this area is comparatively extensive. Intermittent fasting is often compared with a classic energy-reduced diet – here too, however, the results are inconclusive. Some studies suggest that intermittent fasting may be superior to a conventional diet in terms of loss of body fat mass, since less lean mass is lost. Other studies, however, show only minor effects: For example, ten healthy individuals were observed during the 28-day Ramadan. The daily roughly 14-hour food abstinence led only to minimal changes in body mass index (BMI), without significant effects on body composition, cognitive performance or glucose metabolism.
From 16/8 to OMAD: which intermittent fasting method suits you?
Figure 4: There are numerous ways to practise intermittent fasting. The method chosen should fit your daily routine, your physical conditions and your personal preferences.
Not every variant of intermittent fasting is equally suitable for everyone. Depending on health status, physical activity, sex and metabolic conditions, a different approach may be ideal. To give you a clear decision aid, the most popular forms of “intermittent fasting” are briefly presented below.
1. 16/8 method
The 16/8 method is one of the most common variants of intermittent fasting. The principle is simple: an eight-hour eating window is followed by a 16-hour fasting period. Many people find 16/8 intermittent fasting particularly practical for everyday life when the night’s sleep falls within the fasting period. Concretely, this could mean that the first meal is eaten at 11 am and food intake stops at 7 pm. In the time window from 11 am to 7 pm, typically two meals and no snacks or calorie-containing drinks are consumed.
Some experts, however, recommend placing the eating window earlier and skipping dinner. People who want to lose weight in particular could benefit from “dinner cancelling”, as eating earlier usually not only fits better with the circadian rhythm but can also have positive effects on fat metabolism regulation. In addition, avoiding late meals can improve sleep quality and relieve insulin levels.
2. 5/2 method
The 5/2 method involves two fasting days per week, on which you do not completely abstain from food. Instead, a maximum of 20 to 25 percent of required calories should be consumed, which for healthy, normal-weight people corresponds to a daily intake of about 500 calories (women) and about 600 calories (men). On the remaining five days, a balanced diet is important, particularly one that contains enough protein and fibre. It is also recommended not to place the two fasting days directly one after the other and to follow a set rhythm (e.g. always fasting on Mondays and Thursdays).
3. Alternate-day fasting
Alternate-day fasting works on a principle similar to the 5/2 method. On fasting days, about 500 to 600 calories are also consumed. An important difference, however, is the number and frequency of fasting days: because one alternates daily between “fasting” and “normal eating”, alternate-day fasting is also known as the 1:1 method (1 day fast, 1 day normal eating). For many people, this variant of intermittent fasting is harder to maintain than 16/8 or 5/2 fasting, because it offers less social flexibility and hunger feelings on fasting days can be very strong, especially at the beginning of the transition.
4. OMAD method
The abbreviation “OMAD” stands for “One Meal A Day”, which aptly describes the basic principle of this form of intermittent fasting. The entire daily calorie intake is consumed in a single meal. The intended 23-hour fasting phase makes OMAD one of the most extreme forms of time-restricted eating. Besides severe hunger and low energy, the OMAD method also carries the risk of nutrient deficiencies, since all vitamins and minerals required by the body must be provided in one meal.
5. Gentle methods (12/12 and 14/10)
Unlike the OMAD method, which is at most suitable for people with a lot of fasting experience, the 12/12 and 14/10 methods are considered particularly beginner-friendly variants of intermittent fasting. Their effects are milder but often more sustainable than with more restrictive models. The legitimate question arises whether fasting for only twelve or 14 hours can be effective at all. Many scientific investigations answer this in the affirmative. In a study with 19 patients with metabolic syndrome, a daily 14-hour fasting window was observed over three months. Several parameters of cardiometabolic health improved measurably. While longer fasting intervals – such as with the 16/8 method – can support weight loss more strongly, moderate approaches also show positive metabolic effects, particularly on blood sugar regulation and insulin sensitivity.
Who should not do intermittent fasting?
Figure 5: If the body is weakened by undernourishment, hormonal imbalances or certain illnesses, intermittent fasting can place additional strain on the organism.
Intermittent fasting is not equally suitable for everyone. If the body is in a hormonally sensitive state or is already undernourished, an extended eating pause can trigger additional stress. In such cases, the potential negative effects may outweigh the benefits, so fasting could do more harm than good overall. The following groups should either completely avoid intermittent fasting or have their plan supervised by a doctor or dietitian:
- people with eating disorders
- children and adolescents
- pregnant and breastfeeding women
- underweight individuals
- people with thyroid disorders
- people with liver and kidney diseases
- people with certain gastrointestinal diseases (e.g. Crohn’s disease, irritable bowel syndrome)
- people with type 1 diabetes mellitus
- people with cancer
- elderly people
If body fat is very low or body mass index (BMI) is significantly below the normal range, the body often interprets longer eating pauses as an energy shortage. Hormonal imbalances can result. Also in people with disordered eating or eating disorders – even if these occurred in the past – intermittent fasting can reinforce restrictive thoughts and increase the risk of relapse.
In particular, people with type 1 diabetes are at increased risk of hypoglycaemia during prolonged food abstinence, which is why intermittent fasting should only be carried out under medical supervision in such cases. Likewise, intermittent fasting is not recommended during severe infections, in the recovery phase after surgery, or during very intensive training or migraine.
Starting intermittent fasting: 7 tips for a successful start
Figure 6: Every beginning is difficult – this also applies to intermittent fasting. Good planning and a realistic daily structure are the most important basis for successfully starting intermittent fasting.
Intermittent fasting is most effective when it is implemented flexibly, practically and long-term. Intermittent fasting should be seen not as a temporary diet but as a routine that adapts to individual life circumstances. Because the transition can be challenging at the beginning, you will find seven tips below to help you get started with intermittent fasting.
- Start with a gentle rhythm: If long eating pauses are not something you are used to, it is not advisable to start with a strict 16/8 rhythm. Instead, increase slowly. A good entry point is, for example, the 12/12 method (12 hours eating, 12 hours fasting). Once you have got used to this, you can move to 14/10 or 16/8. Alternatively, you can lengthen the fasting window gradually by fasting an hour longer each day. Regularity is more important than perfection. Choose a time window that fits your daily routine, any work and family commitments and your chronotype.
- Prioritise nutrient-rich meals: During eating periods the principle “quality over quantity” applies. Enjoy balanced meals that supply the body with all important nutrients. Protein is particularly important (e.g. legumes, eggs or lean meat), healthy fats (e.g. nuts, seeds, avocado, olive oil) and fibre (e.g. wholegrains, vegetables, fruit). This combination stabilises blood sugar, provides lasting satiety and prevents cravings. You should definitely avoid eating indiscriminately or excessively during eating periods, as this can negate the potential health benefits of intermittent fasting.
- Avoid snacks and double portions: To allow the new rhythm to establish, you should stick to your planned meals during eating periods and avoid constant snacking. Small between-meals snacks keep blood sugar elevated and make it harder to maintain the gaps between meals. Doubling up portions as a “reserve” for an upcoming fasting period is also not sensible. Instead, eat mindfully until you feel comfortably full.
- Drink enough during fasting: Fluid intake is particularly important during fasting periods. Drinking not only supports a stable fluid balance, but can also reduce hunger and headaches, which are common at the start of the transition. Make sure to drink regularly throughout the day. Water, unsweetened teas and black coffee (without sugar or milk) are allowed.
- Adapt your training to intermittent fasting: If you are physically active, you should adapt your training to the chosen fasting model. Light exercise (e.g. walks, yoga or stretching) is generally fine on an empty stomach. For intensive training sessions (e.g. strength training or high-intensity interval training), however, it is often advisable to schedule the activity within an eating window. This ensures the body has sufficient energy during training and recovery is supported by timely nutrient intake. Studies have shown that the combination of intermittent fasting and resistance training is particularly effective for sustainable weight loss while preserving muscle mass.
- Pay attention to your body’s signals: Intermittent fasting should support your health and not cause additional stress to the body. Therefore observe carefully how your body reacts to the change. Persistent tiredness, dizziness, concentration problems or increased irritability can be signs that the chosen fasting window is too large. In such cases it is often sensible to return to a gentler variant.
- Stay flexible: Many people shy away from intermittent fasting because they fear it may not be compatible with their work and social life. Social events such as birthdays, weddings or dinner invitations should still be possible. If, for example, you are invited to dinner and would otherwise skip it, you can instead skip breakfast that day and shift your eating window accordingly. It is this flexibility that makes intermittent fasting truly practicable in everyday life and helps integrate it long-term and without social restrictions.
Disclaimer
This article does not replace treatment by a qualified therapist. The basis of this article is studies and current literature. It must not be used for self-diagnosis or self-treatment. Discuss any inspirations from this article with a therapist you trust if necessary.
About the author
Katharina Korbach regularly writes blog posts about medicinal plants and natural active ingredients for the Narayana Verlag. She became interested in language early on and began writing her own literary texts. A serious illness during her final school years prompted an intensive engagement with health and nutrition topics that continues to this day. After repeated failures of conventional medical treatments, she opted for a more self-empowering, naturopathic therapeutic approach. A plant-based diet was a key factor in her recovery.
Katharina studied Cultural Studies (B.A.) and Applied Literary Studies (M.A.). In 2022 she published her debut novel “Sperling” with Berlin Verlag. Today she works as a freelance author, medical editor and lecturer in Berlin. She spends her free time preferably with friends or doing barre training. She also loves travelling and trying out new vegan recipes.
- Luo L, Qin ZH. Autophagy, Aging, and Longevity. Adv Exp Med Biol. 2019. https://pubmed.ncbi.nlm.nih.gov/31777001/
- Cienfuegos S, Gabel K, Kalam F, Ezpeleta M, Wiseman E, Pavlou V, Lin S, Oliveira ML, Varady KA. Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell Metab. 2020 Sep 1. https://pubmed.ncbi.nlm.nih.gov/32673591/
- Monda A, Casillo M, Allocca S, Moscatelli F, La Marra M, Monda V, Di Maio G, Vasco P, Monda M, Polito R, Messina G, Messina A. Metabolic and Orexin-A Responses to Ketogenic Diet and Intermittent Fasting: A 12-Month Randomized Trial in Adults with Obesity. Nutrients. 2026 Jan 12. https://pubmed.ncbi.nlm.nih.gov/41599851/
- Erlangga Z. et al. The effect of prolonged intermittent fasting on autophagy, inflammasome and senescence genes expressions: An exploratory study in healthy young males. Human Nutrition & Metabolism, Volume 32, 2023. https://www.sciencedirect.com/science/article/pii/S2666149723000063
- Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019 Apr 18. https://pmc.ncbi.nlm.nih.gov/articles/PMC6521152/
- Allaf M, Elghazaly H, Mohamed OG, Fareen MFK, Zaman S, Salmasi AM, Tsilidis K, Dehghan A. Intermittent fasting for the prevention of cardiovascular disease. Cochrane Database Syst Rev. 2021 Jan 29. https://pubmed.ncbi.nlm.nih.gov/33512717/
- Varady KA. Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Obes Rev. 2011 Jul. https://pubmed.ncbi.nlm.nih.gov/21410865/
- Harder-Lauridsen NM, Rosenberg A, Benatti FB, Damm JA, Thomsen C, Mortensen EL, Pedersen BK, Krogh-Madsen R. Ramadan model of intermittent fasting for 28 d had no major effect on body composition, glucose metabolism, or cognitive functions in healthy lean men. Nutrition. 2017 May. https://pubmed.ncbi.nlm.nih.gov/28359370/
- Szekely K, Gerl MJ, Peters B, Schwarz J, Schuppelius B, Damm M, Soliz-Rueda JR, Sehgal R, Lazaratos M, Klose C, Simons K, Pfeiffer AFH, Schürmann A, Kramer A, Michalsen A, Pivovarova-Ramich O. Impact of Intended Isocaloric Early versus Late Time-Restricted Eating on Plasma Lipidome in Women with Overweight or Obesity: Secondary Analysis of the ChronoFast Trial. Adv Sci (Weinh). 2026 Jan. https://pubmed.ncbi.nlm.nih.gov/41186047/
- Obermayer A, Tripolt NJ, Pferschy PN, Kojzar H, Aziz F, Müller A, Schauer M, Oulhaj A, Aberer F, Sourij C, Habisch H, Madl T, Pieber T, Obermayer-Pietsch B, Stadlbauer V, Sourij H. Efficacy and Safety of Intermittent Fasting in People With Insulin-Treated Type 2 Diabetes (INTERFAST-2) - A Randomized Controlled Trial. Diabetes Care. 2023 Feb 1. https://pubmed.ncbi.nlm.nih.gov/36508320/
- Ho Y, Hou X, Sun F, Wong SHS, Zhang X. Synergistic Effects of Time-Restricted Feeding and Resistance Training on Body Composition and Metabolic Health: A Systematic Review and Meta-Analysis. Nutrients. 2024 Sep 11. https://pubmed.ncbi.nlm.nih.gov/39339666/
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12.03.2026
