Everything you need to know about intermittent fasting

Intermittent fasting, also known as intermittent fasting, involves alternating fasting periods with days or hours when you are allowed to eat. This means you only consume calories within a specific time window. The promised benefits include mitigating age-related illnesses and making it easier to lose and maintain weight. Learn here how intermittent fasting works and what it can actually achieve.

What is intermittent fasting?

The principle of intermittent fasting is very simple: There are phases in which you can eat normally, and phases in which you consume no calories. You may only drink plenty of unsweetened tea and water.

What does intermittent fasting mean?

Another name for intermittent fasting is derived from the Latin word "intermittere", which in German means "to interrupt" and "to suspend".

Intermittent fasting, also known as short-term fasting, is a form of fasting. This dietary approach doesn't involve a specific meal plan. Theoretically, anything is allowed during the eating windows. There are no restrictions on specific foods or calorie intake.

Ideally, you should favor healthy foods to meet your nutritional needs. Suitable options include fresh fruits and vegetables, complex carbohydrates, protein, and healthy fats such as rapeseed or sunflower oil.

What happens in the body during intermittent fasting?

The principle of intermittent fasting assumes that the human body has evolved to adapt to periods of fasting. Our ancestors, the hunter-gatherers, did not have continuous access to food and therefore inevitably had to fast regularly.

This dietary pattern with alternating phases of eating and fasting is called intermittent fasting. The human body is accustomed to such fasting periods, which is why intermittent fasting can also be practiced long-term or permanently.

The fasting periods in intermittent fasting typically last between 12 and 36 hours. During this time, the metabolism remains active and does not switch into a "starvation mode" in which energy consumption is reduced. This is a significant advantage over many common diets that, through drastic calorie reduction, can slow down the metabolism and thus often promote a yo-yo effect.

This is how intermittent fasting works.

How does intermittent fasting work? There isn't one single explanation or set of instructions for proper intermittent fasting. Rather, you can choose between different types of intermittent fasting. They differ in the rhythm between eating and fasting periods. You decide for yourself what time you start and end your fast.

The type of intermittent fasting you choose depends on your individual preferences and your discipline regarding food abstinence. Would you prefer to skip breakfast or dinner, or can you easily go a whole day without food? This flexibility makes intermittent fasting attractive to many people.

The choice of an intermittent fasting method affects metabolism. When the body has no energy sources available from food, it first draws on glycogen reserves in the liver and muscles. Once these are depleted, it begins to generate the sugar needed for the brain and other organs from fat reserves. This process is called ketosis. The longer the fasting period lasts, the more pronounced this process becomes.

Various intermittent fasting methods

There are different intermittent fasting schedules with the following rules:

Full days of fasting

Intermittent fasting with full fasting days involves fasting on one to three days per week. This method is often referred to as 6:1, 5:2, or 4:3 intermittent fasting, depending on the number of days fasted per week. On fasting days, solid food is either completely avoided or calorie intake is severely restricted to a maximum of 500-600 calories for women and men.

The permitted calories should preferably come from protein-rich or low-fat foods, while carbohydrates such as pasta, sweets, and alcohol should be avoided. The individual fasting days mustn't be consecutive to allow the body sufficient time to regenerate.

36:12 rhythm

With the 36:12 fasting method, you fast every other day. On an eating day, you can eat normally between 8 a.m. and 8 p.m. This is followed by a 36-hour fasting period, which includes the night and the entire following day, during which you consume only liquids such as water or unsweetened tea.

20:4 rhythm

With the 20:4 intermittent fasting method, you have a four-hour eating window each day. During the remaining 20 hours, you fast, meaning you don't consume any solid food. During the fasting period, only calorie-free liquids such as water, unsweetened tea, or black coffee are permitted.

16:8 rhythm

With this practical model, you fast for 16 hours each day and eat for eight hours. This is achieved, for example, by skipping breakfast or dinner.

14:10 rhythm

With the 14:10 intermittent fasting method, you fast for 14 hours each day, during which you consume no solid food. You then have a 10-hour window for eating. This type of intermittent fasting is often considered particularly suitable for women, as their bodies begin to draw on fat reserves after about 14 hours.

Women in their 40s or 50s who are going through menopause and struggling with weight gain or increased abdominal fat often use this method. The 14:10 rhythm can help support metabolism and promote fat burning without requiring long fasting periods.

Sometimes this variant is also called dinner-cancelling, in which dinner is skipped to extend the overnight fasting period.

Other intermittent fasting methods

There are other intermittent fasting models as well. The 12:12 variant is particularly suitable for beginners who initially find it difficult to abstain from food for extended periods.

A very extreme form of intermittent fasting is the 23:1 method. With this method, you are only allowed to eat for one hour a day. In the US, it's called "One Meal a Day." The 23:1 method is not suitable for long-term use. Use this method only for a few consecutive days or once a week.

How long can you do intermittent fasting?

If you don't opt ​​for the extreme 23:1 intermittent fasting method, you can practice short-term fasting continuously without a break. You must eat a healthy and balanced diet during your eating windows. Also, drink plenty of fluids.

Beginners can proceed slowly and start with the 14:10 or 16:8 method.

There's nothing wrong with slightly adjusting the times if that fits better into your daily routine. One or two hours is no problem.

A so-called "cheat day" is also possible. If you have opted for the 36:12 rhythm or entire fasting days, you can generally eat as you please on the permitted eating days.

It's generally not a major problem to interrupt intermittent fasting for a weekend. However, this should remain the exception, as otherwise the effects of intermittent fasting will be disrupted. Breaks often also increase the dropout rate.

What is allowed during intermittent fasting?

Many people who start intermittent fasting are unsure what is allowed and what isn't. We answer the most important questions.

What can I eat during intermittent fasting? Basically, anything is allowed. There's no meal plan or food list. However, make sure you eat a balanced diet with plenty of vitamins, minerals, and fiber.

Can I eat sweets while intermittent fasting? Yes, that's generally allowed. However, it's not beneficial for your health or weight loss. Sweet foods often have a high sugar content and are high in calories. It's better to choose fruit.

What can I drink during intermittent fasting? Water and unsweetened herbal teas are best. Ginger, cucumber, and lemon water are also permitted. While sugary drinks and alcohol are allowed during eating windows, consume them sparingly.

Can I drink coffee while intermittent fasting? During the eating window, it's no problem. Black coffee is also permitted during the fasting period. However, coffee with milk is a different story during this phase. Milk contains lactose, which affects blood sugar levels. Coffee with oat milk or almond milk, on the other hand, is allowed during intermittent fasting – but only in small amounts. Bulletproof coffee, which is coffee with butter and oil, is also currently trending. It can also be consumed during the fasting phase because it doesn't affect insulin levels and even stimulates fat burning.

Can I use sweeteners while intermittent fasting? Artificial sweeteners like aspartame are not recommended. They can trigger cravings. Diet sodas are also best avoided. However, natural sugar substitutes like stevia, xylitol, and others are metabolized without insulin and therefore do not affect blood sugar levels.

Is it okay to chew gum while intermittent fasting? There's nothing inherently wrong with chewing gum. However, it can increase feelings of hunger for many people. Therefore, it's questionable whether chewing gum is beneficial during a fasting period.

Side effects of intermittent fasting

Intermittent fasting has disadvantages for the body. Fasting puts stress on the body. Those who are very stressed at work and in their daily lives should avoid intermittent fasting. This also applies to people with diabetes. On fasting days, there is a high risk of hypoglycemia (low blood sugar).

Because low-calorie intake during the fasting phase leads to low blood sugar levels, headaches can occur. If these persist, you should re-evaluate whether your chosen method is right for you and, if not, consult a doctor. The latter also applies if you are taking medication.

Please note that bad breath can occur on fasting days due to the lack of carbohydrates – a side effect of ketosis. Therefore, drink plenty of fluids or suck on sugar-free candies.

People who skip breakfast should see if coffee on an empty stomach is good for them.

Women who are pregnant or breastfeeding should also avoid fasting to ensure their child receives enough energy and nutrients throughout the day.

Those who are physically active and want to build muscle during intermittent fasting should consume enough calories and protein. If this is followed, intermittent fasting can be practiced without problems. Studies have even shown positive effects on the release of human growth hormone (HGH), which influences muscle growth.

Intermittent fasting can also be unhealthy if your diet is primarily high in sugar and fat. Since there are no specific food recommendations, the German Nutrition Society advises against it for long-term weight loss.

If you primarily consume white flour products, fast food, and sweets during your eating windows, you may still gain weight despite intermittent fasting. Then it may seem as if intermittent fasting is ineffective.

Effects of intermittent fasting

Although numerous studies on intermittent fasting in humans now exist, evidence of a life-extending effect remains lacking. Most studies only ran over short periods, which is why there are no conclusive long-term studies yet.

Is intermittent fasting healthy?

Intermittent fasting takes advantage of the fact that during calorie-free periods, a process called autophagy is triggered in cells after 14 hours. In this process, cells break down old and defective building blocks, and the body removes waste products. This could explain the sometimes surprising health effects of fasting.

Intermittent fasting may also prevent or improve various illnesses. These include joint problems, cardiovascular diseases, diabetes, and skin conditions such as eczema and acne. Fasting may even offer protection against certain types of cancer.

Effects of intermittent fasting

Although numerous studies on intermittent fasting in humans have now been published, evidence of a life-extending effect remains lacking. Most studies only ran over short periods, which is why there are no conclusive long-term studies yet.

Is intermittent fasting healthy?

Intermittent fasting takes advantage of the fact that during calorie-free periods, a process called autophagy is triggered in cells after 14 hours. In this process, cells break down old and defective building blocks, and the body removes waste products. This could explain the sometimes surprising health effects of fasting.

Intermittent fasting may also prevent or improve various illnesses. These include joint problems, cardiovascular diseases, diabetes, and skin conditions such as eczema and acne. Fasting may even offer protection against certain types of cancer.

Further discussed benefits of intermittent fasting include:

• helps with fat burning
• inhibits inflammatory processes
• reduces cholesterol levels
• Relieves chronic constipation
• lowers blood pressure
• Helps with irritable bowel syndrome with diarrhea and bloating
• can support the growth of new nerve cells (protection against Alzheimer's disease)

Does intermittent fasting help with weight loss?

Intermittent fasting is not a traditional diet. However, it can aid weight loss when combined with a healthy, balanced diet and regular exercise. It usually takes two to three weeks for the body to adjust and for initial results to become apparent.

The amount of weight you lose varies – some people lose half a kilogram a week, others two. It also depends on what you eat.

Women in menopause can lose weight through intermittent fasting, but it's not a given. They probably won't lose the typical belly fat with this method alone. For them too, exercise and a healthy diet are essential for shedding pounds.

Whether intermittent fasting generally helps reduce unhealthy belly fat is controversial.

Who should not do intermittent fasting?

You should not do intermittent fasting if you.

• suffer from diabetes
• have low blood pressure
• taking medication
• are underweight
• to suffer from an eating disorder
• Are you pregnant or breastfeeding
• to struggle with menstrual irregularities

Intermittent fasting: Conclusion

Intermittent fasting is a type of fasting that can be easily integrated into everyday life and is also relatively easy to stick to compared to longer fasting periods. The method is also suitable for changing one's eating habits, losing weight, or maintaining a healthy weight.

Start with short fasting periods (16 hours) and carefully consider whether your current life situation (stress level) is a good time for intermittent fasting. If you can answer yes, and you are healthy, balanced, and reasonably disciplined, then there's nothing stopping you from starting this eating rhythm.

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