Intermittent fasting, also known as intermittent fasting, is now far more than just a trend and was already part of everyday life for some people before intermittent fasting even came about. Most people skipped breakfast because: “I’m just not hungry in the morning.” (As people usually eat more/too much and late in the evening.) Or: “I don’t have time for breakfast.” (Because people prefer to stay up late in the evening and then the alarm clock doesn’t ring until just before dawn).
Many positive effects of intermittent fasting are shown in terms of weight loss, metabolism, cell repair and even brain health, which some studies also prove. But are there only positive effects and is it for everyone?
In this blog post, you will find out everything you need to know about intermittent fasting and how you can make the most of this method – or not.
An overview of the most common interval fasting methods
There are different types of intermittent fasting, which basically all aim to adhere to certain fasting and eating times. Here is a brief summary of the best-known ones for you:
- 16:8 method: This method of intermittent fasting is particularly well known and involves 16 hours of fasting followed by an 8-hour window for eating. This means that you eat between 12:00 and 20:00, for example, and then fast until the next day. This method is suitable for many beginners and is usually easy to integrate into everyday life.
- 5:2 method: With the 5:2 method, you eat “normally” five days a week, while on two days your calorie intake is limited to around 500-600 calories. It is also known as part-time fasting and is still relatively easy to implement as it is flexible and less restrictive than other fasting methods. The two fasting days do not have to/should not be directly consecutive so that the metabolism is not affected too much.
- Alternate-Day Fasting (ADF): Alternate-day fasting involves alternating between fasting days with minimal calorie intake (0-500 kcal per day) and days without calorie restriction. This method is more suitable for advanced fasters, as keeping up the fasting days can be a challenge.
- Eat-Stop-Eat: This method involves a 24-hour fasting phase once or twice a week. An example would be fasting from one evening meal to the next. Eat-Stop-Eat is suitable for people who already have experience with shorter fasting phases.
- Warrior diet: This is a fasting model in which you eat minimally for 20 hours, followed by a 4-hour “feast”. This method is intended for very experienced fasters.
Now you have an overview of the basic types of intermittent fasting. But what are the supposed benefits that might make intermittent fasting interesting for you too?
The benefits of intermittent fasting
Weight loss and body fat reduction through intermittent fasting
One of the most frequently asked questions about intermittent fasting is whether it helps with weight loss. Yes, studies show that intermittent fasting activates fat metabolism, as the body uses fat reserves for energy during the fasting phases. According to a meta-analysis by Harris et al. (2018), intermittent fasting has comparable or even better effects on weight loss than continuous calorie restriction. The 16:8 diet and alternate-day fasting in particular support fat loss without losing significant muscle mass. It is important here that the protein intake is kept correspondingly high.
Improved insulin sensitivity and blood glucose control
Intermittent fasting is also a popular topic in the context of improving insulin sensitivity. Studies, such as the one by Sutton et al. (2018), show that early time-restricted fasting (e.g. eating only in the morning hours) can improve insulin sensitivity and stabilize blood glucose levels. This is a key benefit as it can reduce the risk of type 2 diabetes.
Reduction of inflammation levels and promotion of heart health
Another frequently cited effect of intermittent fasting is the reduction of inflammatory markers in the body. Meta-analyses, such as the one by de Cabo and Mattson (2019), show that intermittent fasting lowers inflammation levels and thus reduces the risk of cardiovascular disease. Intermittent fasting can also help to lower LDL cholesterol levels (often referred to as ‘bad’ cholesterol) and triglyceride levels, which contributes to long-term heart health.
Promotion of autophagy and cell repair
Another buzzword in the field of intermittent fasting is autophagy. This process, in which the body breaks down and recycles damaged cells, is stimulated by periods of fasting. According to Madeo et al. (2015), intermittent fasting supports cell repair and could therefore counteract age-related diseases such as Alzheimer’s and Parkinson’s. Autophagy is a crucial mechanism that can contribute to a healthier and potentially longer life.
Brain health support and cognitive benefits
Intermittent fasting is also increasingly associated with positive effects on brain health and mental clarity. A study by Mattson et al. (2018) shows that intermittent fasting increases the production of brain-derived neurotrophic factor (BDNF), which is important for learning and memory. This effect could also prevent neurodegenerative diseases such as Alzheimer’s and support cognitive function.
Promotion of gut health
Intermittent fasting can have a positive effect on the microbiome, as recent studies suggest. According to an analysis by Li et al. (2020), intermittent fasting increases the diversity of gut bacteria and reduces pro-inflammatory microbes. A healthy microbiome is crucial for the immune system and general health and could be strengthened by regular periods of fasting.
Intermittent fasting is therefore undoubtedly a trend that can make sense for many due to its many supposed benefits. Nevertheless, there are also a large number of studies and analyses that point to potential risks and limitations. These should be taken into account when deciding on intermittent fasting, as not everyone benefits equally from this method.
The disadvantages of intermittent fasting
Long-term effects on the metabolism
Intermittent fasting can have a negative impact on the metabolism, especially when used over a long period of time. Studies, such as the meta-analysis by Trepanowski and Bloomer (2010), indicate that longer periods of fasting can cause the basal metabolic rate to fall. The body adapts to the reduced energy intake, which could hinder fat burning in the long term and even trigger a yo-yo effect as soon as the calorie intake is increased again. This is an important point to bear in mind when choosing a method such as the 16:8 diet or alternate-day fasting.
Negative effects on the hormone balance
A common criticism of intermittent fasting is its impact on hormone levels, particularly in women. Studies, such as that by Heilbronn et al. (2005), have shown that fasting can reduce the production of leptin – a hormone that regulates hunger and energy levels. In women, this can lead to menstrual irregularities and other hormonal imbalances, especially if intermittent fasting is practiced for long periods of time or in extreme variations.
Mental health and eating behavior
Critical studies, such as that by Harvie et al. (2011), show that intermittent fasting can increase the risk of disordered eating behavior, such as binge eating. This is particularly problematic for people with a history of eating disorders. Periods of fasting can increase the desire to overeat during the eating window, which can undermine the positive effect of intermittent fasting on weight loss in the long term.
Lack of long-term safety studies
One of the most common criticisms of intermittent fasting is the lack of long-term studies. Although short-term studies show positive effects such as weight loss and an improvement in insulin sensitivity, it is unclear whether these benefits persist in the long term. According to the meta-analysis by Seimon et al. (2015), there is insufficient evidence to date that intermittent fasting is safe over several years.
Blood sugar problems in certain groups of people
Although intermittent fasting is often recommended to stabilize blood sugar, certain groups may experience negative effects. A study by Sutton et al. (2018) shows that some participants experienced increased insulin resistance when fasting was irregular or lasted too long. This can be particularly problematic for people with type 2 diabetes and requires individual adaptation of the fasting method.
Loss of lean mass
A potential disadvantage of interval fasting, especially in the absence of protein intake or strength training, is the loss of muscle mass. The meta-analysis by Varady et al. (2011) shows that prolonged periods of fasting can reduce muscle mass if not combined with sufficient protein and exercise. However, muscle mass is crucial for basal metabolic rate and long-term weight control.
The conclusion to intermittent fasting
As you can see, intermittent fasting can offer you some potential benefits. However, there are also some critical points that should not be ignored.
As a personal trainer, I can tell you from experience that I rarely, if ever, use intermittent fasting with my clients. It can sometimes make sense to introduce intermittent fasting for a limited period of time, especially at the beginning of your work together, depending on your previous eating habits and current body fat percentage. Giving your stomach and intestines a rest, especially if your diet is full of sugar, convenience foods, fast food and alcohol.
However, for most people it means even more stress in the short or long term. Because it also means stress for the body to go without food for a “longer” period of time. More stress that is also added to the already stressful lifestyle of most people today. The hormone cortisol – also known as the “stress hormone” – plays a role here, as permanently high cortisol levels have a negative effect on body fat reduction. And for most people, the stress level is already so high that it usually makes little sense to further increase this effect through intermittent fasting. A constant blood sugar level throughout the day, which requires regular meals, usually makes more sense here.
In addition, there is no clear difference or advantage in terms of body fat reduction whether you carry out intermittent fasting or a calorie deficit with regular meals.
I wish you every success in achieving your goals – with or without intermittent fasting.
Sources:
- Harris, L., Hamilton, S., Azevedo, L. B., et al. (2018). “Intermittent fasting interventions for treatment of overweight and obesity in adults: A systematic review and meta-analysis.” Obesity Reviews.
- Sutton, E. F., Beyl, R. A., Early, K. S., et al. (2018). “Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even Without Weight Loss in Men With Prediabetes.” Cell Metabolism.
- de Cabo, R., & Mattson, M. P. (2019). “Effects of Intermittent Fasting on Health, Aging, and Disease.” New England Journal of Medicine.
- Madeo, F., Carmona-Gutierrez, D., Hofer, S. J., & Kroemer, G. (2015). “Caloric Restriction Mimetics against Age-Associated Disease: Targets, Mechanisms, and Therapeutic Potential.” Cell Metabolism.
- Mattson, M. P., Moehl, K., Ghena, N., et al. (2018). “Intermittent metabolic switching: Preclinical and clinical evidence for the role of periodic fasting in health and disease.” The Lancet Diabetes & Endocrinology.
- Li, G., Xie, C., Lu, S., et al. (2020). “Intermittent fasting promotes a healthy gut microbiome by reshaping the gut environment: Evidence from experimental and clinical studies.” Nature Communications.
- Trepanowski, J. F., & Bloomer, R. J. (2010). “The impact of religious fasting on human health.” Nutrition Journal.
- Heilbronn, L. K., Smith, S. R., Martin, C. K., et al. (2005). “Alternate-day fasting in nonobese subjects: Effects on body weight, body composition, and energy metabolism.” American Journal of Clinical Nutrition.
- Harvie, M., Wright, C., Pegington, M., et al. (2011). “The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: A randomized trial in young overweight women.” International Journal of Obesity.
- Seimon, R. V., Roekenes, J. A., Zibellini, J., et al. (2015). “Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials.” Molecular and Cellular Endocrinology.