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Intermittent Fasting – What exactly is it?
Intermittent Fasting (IF), also known as interval fasting, is a form of fasting that involves abstaining from food and drink intake in a defined rhythm (hourly or daily). The effects of interval fasting include, for example, weight reduction and metabolic regulation by influencing the biorhythm, the gut microbiome, and lifestyle (e.g., sleep). In contrast to many other diet forms or pure calorie restriction, interval fasting is much easier to adhere to.
How it works
There are various forms of IF that can be applied. The two best-known methods are:5:2 MethodWith this method, you eat normally for five days a week without calorie restriction. On the remaining two days, calorie intake is then completely restricted or limited to approximately 500 kcal. It is important to note that the two fasting days should not be consecutive.Studies in humans have shown that this fasting method leads to a significant reduction in weight, fasting insulin levels, and fasting glucose levels. Furthermore, some study participants reported a reduction in tension, anger, and fatigue, as well as an increase in self-confidence and mood. Studies show that it is generally much easier to stick to fasting on alternate days than to everyday calorie restrictions.If you limit your calorie intake to approximately 500 kcal on fasting days instead of completely abstaining from food, there are some helpful tips to consider:
- Most people find it easiest to eat one large meal late in the day. Alternatively, and even healthier, you might prefer to eat early or spread your food intake over 2 meals. Experiment to find what works best for you.
- On these days, the focus should be on low-calorie vegetables, protein-rich foods, and good fats, e.g., in the form of soups, to feel satiated. Good examples include: grilled salmon, other fish or chicken with vegetables, eggs with shrimp, vegetables and olive oil, mixed salad with olive oil, avocado and salmon, chicken-vegetable soup, spinach, onions with salmon, vegetables with cashews, tomato soup with shrimp.
16:8 MethodIn this most widespread form of IF, food intake occurs within an 8-hour window, followed by a 16-hour fasting period. The positive effects of the fasting period become noticeable after just 12-14 hours. The optimal duration for abstaining from food is 14-16 hours (max. 18 hours). The charm of this method lies in its simplicity. Due to sleep, during which no food is consumed anyway, most people find adhering to 13-16 hours of fasting per day not only much easier than expected but also quickly integrate it into their lives – especially because the many positive effects are quickly noticeable for most.How does it work?
- It is best to eat your last meal early in the evening – before 8 PM in summer and before 5 to 6 PM in winter – and then abstain from food for 16 hours. IF also shows positive effects if you eat later in the evening. The essential point is to maintain a gap of 13 to 16 hours before the next food intake.
- During the fasting period, calorie-free beverages such as water, unsweetened coffee, herbal tea, or green tea can be consumed.
That’s all you need to know to get started.Special tips:
- During the eight hours, eat no more than two to three times and focus on nutritious foods. This includes avoiding soft drinks/fruit juices, sweets, ready meals, bread, and red meat, while also consuming a variety of vegetables, mushrooms, fruits, healthy fats (such as olive oil, fatty fish, avocado, nuts), and good proteins (e.g., eggs, chicken, fish, and nuts, etc.).
- It is ideal to exercise two to three times a week on an empty stomach, for example, interval training or light endurance training. This further improves the uptake of sugar into the mitochondria – our powerhouses – and the production of ATP, the main energy store in our cells.
Is Intermittent Fasting safe?
Most, if not all, studies suggest that intermittent fasting is safe and tolerable and can lead to a weight loss of 3-8% in adults with overweight or obesity, also as a sustainable lifestyle.Diabetics should only practice intermittent fasting under medical supervision. In cases of problems with the pancreas and thyroid, as well as the adrenal glands, e.g., in severely overweight individuals, a low-carb diet should first be started or only in consultation with your doctor.Otherwise, it is suitable for people who want to support their health or lose weight.
Effects and Benefits
Weight Reduction
Severe overweight and especially obesity represent a global health problem due to the resulting risk factors for cardiovascular diseases and type 2 diabetes, among others. To prevent the onset and progression of these secondary diseases, weight reduction has established itself as a key strategy. Several current systematic reviews have even shown that intermittent fasting leads to significant weight loss.
Metabolic Regulation
Intermittent fasting also has a positive impact on a variety of markers and risk factors, such as those for cardiovascular diseases, myocardial diseases (cardiomyopathy), inflammatory parameters, metabolic diseases, cancer, retinal damage (retinopathy), neuroplasticity, cognition, and lifespan. Intermittent fasting appears to achieve more positive metabolic effects than pure calorie restriction.
Inflammation
Important parameters for inflammatory status are homocysteine, interleukin 6 (IL6), and C-reactive protein (CRP). Among many others, a recent study from 2019 also showed that intermittent fasting leads to a reduction in the aforementioned parameters.A factor for an excess of inflammation in the body is eating too much and too frequently. Therefore, it is not surprising that interval fasting and calorie reduction are indeed essential measures to reduce low-grade systemic inflammation – which is considered a main cause of many chronic diseases. Thus, by reducing inflammatory and autoimmune processes in the body, diseases such as cardiovascular diseases, type 2 diabetes, cancer, fatty liver, type 2 diabetes and obesity, multiple sclerosis, asthma, and psoriasis are affected. In addition, calorie reduction and IF slow down the aging process and prolong life.A 2019 study also clarified how IF can reduce inflammation in the body, namely by reducing the number of circulating monocytes – which are phagocytes or precursors of phagocytes in the blood – as well as their metabolic and inflammatory activity. Fasting improves inflammatory diseases without impairing antimicrobial immunity. Both IF and alternate-day fasting are as effective as calorie restriction in reducing insulin resistance.Insulin resistance is a major mechanism for low-grade inflammation in the body and, among other things, leads to diabetes in the long term. Try which type of fasting is easier for you. For me, 16/8 works easiest.
Oxidative Stress, Mitochondria, and Longevity
A Harvard study from 2017 found that mitochondria, the powerhouses of the cell, can be influenced by fasting to be kept in a “youthful” state, leading to better health and longevity.Oxidative stress refers to an imbalance between oxidative and antioxidative processes and leads to impairments in cell membranes, proteins, and enzymes. It promotes aging processes and damage to genetic material. Studies have shown that IF reduces oxidative stress and has an antioxidant effect.
Fat Composition
Intermittent fasting has been found to lead to a significant improvement in total cholesterol, low-density lipoprotein cholesterol (LDL), and triglycerides. These are the unhealthy fats in the body that promote the development of cardiovascular diseases and inflammation of the pancreas. It is therefore very beneficial that IF reduces these fat levels. In animal studies, fasting days not only showed an improved blood sugar and fat profile but also more efficient mitochondrial respiration in skeletal muscle. Fat burning is promoted by IF.
Circadian Rhythm
Circadian rhythm is the ability to synchronize physiological processes to a period length of approximately 24 hours. Desynchronization of peripheral circadian clocks in liver, fat, and muscle cells, e.g., caused by eating at night, can increase the risk of certain chronic diseases such as cardiovascular and/or metabolic diseases and cancer. Intermittent fasting, on the other hand, promotes optimal synchronization of the hormonal response.
Microbiome
Initial animal models suggest that IF has positive effects on gut microbiota, as our gut also follows circadian rhythms. These can synchronize better by restricting food intake to a few hours a day. Intermittent fasting can also directly affect the microbiome by contributing to the diversity of the gut microflora.
Cognition
Intermittent fasting improves memory and cognition in animal studies.
Health Behavior and Sleep
Intermittent fasting has the potential to influence people’s health behavior. Numerous observational studies show that nocturnal eating is associated with reduced sleep duration and poor sleep quality, which can lead to insulin resistance and an increased risk of obesity, diabetes, cardiovascular diseases, and cancer.One study found that a nocturnal fasting duration of more than 14 hours led to significant weight loss as well as improvements in sleep satisfaction, bedtime satiety, and energy levels.
Conclusion
Studies on IF suggest that it can prolong life and have a positive influence on general health, particularly in cases of cardiovascular and/or metabolic disorders. However, further large-scale studies with long-term data and scientifically validated recommendations for food choices within the eating periods are needed.Based on the results so far, it seems worthwhile to try intermittent fasting and observe what changes it brings about for oneself. Especially in combination with other healthy lifestyles such as more exercise and regular breaks from sitting, the effect of IF can be further enhanced. It is also advisable to combine interval fasting with a diet of high-quality healthy foods (see above).
