Did you know that in the 1990’s it was widely believed that if you wanted to get in shape, you had to eat six high-protein meals a day? This has remained a common belief over the years. But the idea shifted in the early 2000’s with the introduction of the ‘Warrior Diet’. This diet is based on the eating patterns of the ancient Roman centurions. They fasted for the majority of the day and had a big feast in the evening. This technique was later coined intermittent fasting (IF). But, what is intermittent fasting? We will tell you everything you need to know, and why you should give it a shot!

For some of us, it sounds weird and maybe extreme to have more hours in the day being fasted than being fed. But actually, this is very normal. Our bodies are designed to store energy and can survive for many days without food. But don’t worry, we don’t need to fast for a week in order to experience the benefits. The most popular diet consists of a 16-hour fasting window followed by an 8-hour eating window. During the fasting window, we consume no calories, but it is important to drink water or tea to stay hydrated. The most common reason people follow an IF diet is to maintain a healthy body weight. But did you know IF could also benefit our cognitive function, mood, brain health, and even life span?

Losing weight. One out of every two US citizens tries to. ¹ More and more people are trying IF to achieve their goals. Recent studies show that IF is indeed an effective tool. ² And it makes sense. With smaller eating windows, meaning less time to eat, it’s simply more difficult to overeat. Most people will naturally eat less during the day because there is less time to eat.

What is intermittent fasting and the effect of ketosis? Well, when we eat, we store the excess energy for later. First, let’s say that during breakfast, we store energy in the form of sugar in our liver. In the following hours, we can use that sugar to provide our body with needed energy. During lunch, we replenish the sugar stores again.  If we don’t, our livers will run empty. After approximately 16 hours of fasting, the sugar levels are completely depleted. At this point, we need to get our energy from elsewhere. And that’s where fat burning comes in. The liver starts to produce ketone bodies. This process is called ketosis. The ketone bodies are large transport molecules that bring fat from the skin to the liver. The liver burns the fat, and we have energy again.

So, that’s the power of intermittent fasting. The body will actually switch from burning sugar to burning fat after a short fast. We might have felt a bit tired until this moment. But when our bodies start to burn fat, we feel better again. That is because our metabolism slows down during fasting until the switch from sugar to fat burning happens ^3,4 . You can see your liver as a battery. As the energy stores diminish, the light will be less bright; we are burning fewer calories and feel a bit tired. But after 16 hours, we basically switch to another battery (our fat tissue)—and a big one. The light will be brighter again, meaning we will burn calories quicker and feel more energized.

So how do we do it? Intermittent simply means that something is coming and going at intervals. With fasting, that could be an interval of 16 hours every 24 hours, like the most popular variant. You could fast from 8 p.m. to noon the next day, for example. During the fasting window, no calories should be consumed. That doesn’t mean you can’t consume anything. Drinking enough water during the fast is very important. Coffee and tea are suitable alternatives as long as we consume them without milk and sugar, of course.

As ketosis will kick in after about 16 hours, elongating the fasting window to 18 or even 20 hours might provide more benefits. This way, you spend more time in ketosis. However, this is a more advanced protocol. We recommend getting used to 16:8 first. Another popular approach is the 5:2 schedule. People eat normally for five days during the week and fast for the remaining two days. Oftentimes, calorie intake isn’t zero but rather limited to 500 calories on fasting days. This is the beauty of intermittent fasting. You can do it however it suits you; there are way fewer rules than on other diets.

Intermittent fasting is more than weight loss. It might actually help us live longer. When we fast, our bodies will start recycling old and damaged cells. ⁵ We call this process autophagy. It’s very important to recycle damaged cells because they don’t work properly anymore. And if cells don’t function, they can even develop into cancer cells.

  ⁶ On top of that, intermittent fasting slows down inflammation and oxidative stress. ^7,8 These are processes that can damage our cells if they are too active. And even our hormone balance might improve! Intermittent fasting can reduce insulin and homocysteine levels, lowering the risk of heart disease. ^5,7 Altogether, intermittent fasting could be a very powerful tool to prolong life. In fact, studies already show that IF increases lifespan in rats and other animal models by up to 80%! This suggests promising potential for humans. ^9,10

 If that wasn’t enough, intermittent fasting could also help us maintain a healthy gut. Animal studies have shown that the IF diet increases the number of good bacteria and reduces the number of bad bacteria. ^11,12 Human trials have also shown improvements in the gut flora. ¹³ And a healthy gut is not only important for longevity but also prevents discomforts such as cramps, bloating, and constipation.

The effects of intermittent fasting that might be less obvious are the improvements in mood and mental health. In a large study, IF reduced anxiety and depression symptoms in participants. ¹⁴ Also, IF is often claimed to reduce stress. However, caution should be taken, as our cortisol levels are shown to rise as soon as fasting starts. ¹⁵ Cortisol is a stress hormone. High fluctuations in it can negatively affect our mental health.

 Still, IF seems beneficial for overall mental health and has even been shown to improve brain plasticity. That means increased functionality and becoming more resistant to stress, injury, and disease. ¹⁶ Even brain diseases such as Alzheimer’s could be slowed down or modulated by IF in animal models. ^17–19 Today, researchers are investigating whether IF could actually prevent this disease’s onset in humans.

It’s not all sunshine and rainbows, though. Although the diet gives a lot of freedom, it might still be hard to sustain. On top of that, people often report side-effects like reduced energy and problems sleeping. Headaches, dizziness, and nausea also belong to the list. Increased cortisol and insulin fluctuations are often at the root of these issues. It’s a good idea to contact your doctor before starting IF. Especially if you are pregnant, breastfeeding, or have a history of eating disorders. People with diabetes type 1, people who are taking medicines, and people of old age should also be careful.

Altogether, there are more than enough reasons to try intermittent fasting. Whether you want to lose weight, maintain a happy mind, or simply enjoy life longer, IF could be your fix. However, it is no excuse to eat everything we want. IF should be combined with a diet consisting of healthy foods. It’s important to pick a schedule that fits you. Start slow and listen to your body. You might love it! But remember that your wellbeing should always come first.