Is Now the Best Time to Fast? The Doctor Says Yes

Is Now the Best Time to Fast? The Doctor Says Yes

Interview With Andreas Michalsen, MD, PhD


Dr. Andreas Michalsen, author of The Fasting Fix, uses fasting to treat a number of diseases from osteoarthritis, rheumatoid arthritis, diabetes, and hypertension to cardiovascular disease, early stages of dementia, Crohn’s disease, and irritable bowel disease.

Andreas Michalsen, MD, PhD, is the director of a hospital in Berlin with beds for 90 patients. Typically 90 percent of those patients are fasting. Why? Because he believes the diseases these patients present—osteoarthritis, rheumatoid arthritis, diabetes, hypertension, cardiovascular disease, early stages of dementia, Crohn’s disease, irritable bowel disease—are all an indication for fasting. When Dr. Michalsen does rounds, sometimes his younger doctors say, “Isn’t this a little bit exaggerated? Surely, everything can’t be cured by fasting.” Dr. Michalsen replies, “Fasting is not a miracle, and not all diseases are cured. But fasting is how you start the way back to health.” It’s also the classic start of a spiritual journey.

In your latest book, The Fasting Fix, you write that you first had to accept your own family medicine.

Yes. I’m from a family of MDs, but they were all natural doctors. My grandpa was a natural doctor. My father was a natural doctor. So, I was a bit bored as a child because it was always about herbs and nutrition and water. Then about age 16—when you are against everything your father is doing—I started to eat junk food and to smoke. When I started study- ing medicine, I was still smoking and eating junk food. I loved cardiology and intensive care, and I thought what my father was doing was not real medicine.

Then it happened—as it must happen. I had an examination from the hospital, and my blood pressure was high and my cholesterol was over 200. I thought, “Oh my God! I’m only 29 years old. This is really not good news.” Two years later, my lifestyle still was very bad. I worked the nightshift, eating cakes and sausage and coffee and smoking, and the results were worse. That’s when I said, “Okay, stop. I have to change.” And I remembered what I knew about a plant-based diet and relaxation. It worked, and I got healthy again.

You’ve said that everything we eat is a foreign body. I’ve never really thought about food that way. I typically think about food as fuel.

Everything that we ingest is an attack in the first moment. The immune system has to first regard any food as an enemy—and then to specify and to differentiate: Okay, this is fine. This is a tomato. And maybe this is not fine: This is poison. When we regard food from a molecule perspective, in the first moment, all digestion is a kind of inflammation.

What we eat is an enormous immunological burden for the whole gastrointestinal tract. The microbiome is so very complex because the task of digestion is so complex. Sometimes I think it’s a miracle that it works so well. A lot of people can eat awful things for years, and yet they’re still here.

So, when I look at a banquet table and start to salivate, to my mind that’s really exciting. But my body is gearing up for a lot of work.

It is a lot of work. And therefore, it is very important to ease into that work. I really like the American businessman Horace Fletcher, who worked with Doctor Kellogg from the cereal company. Fletcher was not a doctor, but realized a long time ago that we should chew extensively because chewing prepares the digestion. By chewing we give attention to the process of digestion. We now call it mindful eating. We should be mindful that digestion is a very complex process, and we should support our body as well as we can. Taking digestion for granted is one reason we see so many people today with food allergies or intolerances.

You write that every religious tradition includes fasting. And that shamanic practices often begin with fasting. Now that makes sense to me in a new way. If every food is actually a foreign entity entering the body, the first step for a shamanic practice is get rid of foreign entities. Is that essentially what you’re saying?

Yes. This is an historical or archetypal view. Maybe a semantic view. But let me paraphrase it like this: In every religion, in every spiritual context, there are fasting rituals and they prepare the body and mind for something higher or for something special.

When you fast, two things come to the front of your perception. One is time: You don’t have to spend time buying food, preparing food, eating food. Your digestion also decelerates, so you are less burdened with the material intake. All that is gone. Instead of shopping and cooking and eating and digesting, one sip of water is what I’m doing now. So, fasting creates free time, an expansive sense of time, and a lighter sense of being. Wow, I have no material stuff and I’m living.

The second effect is that your senses become sharper and clearer. I think this is an evolutionary trick because if you’re a caveman and food is scarce, it would not be a good idea then to say, “Oh, I’m very sleepy. I have no time for the search for food.” If food is scarce, you have to be alert, your senses have to work.

So, all this comes together.

So a fast is a way of getting back in touch with oneself?

Yes, exactly. As a researcher, I focus on the molecular aspects of fasting. And that’s very important. But when you’re actually fasting, what strikes everybody is this feeling of awareness. I saw two or three patients today that were at the sixth day of fasting, and one of them had already lost five kilograms. So, I said it was time to stop. But he wanted to continue fasting because he felt so great. So, we made a deal. I said, “Okay, two more days, but then you have to stop.” He was a little bit maniac about fasting.

I’ve read and written about sugar and salt as being unhealthy, but I’d never thought about using sugar to disguise poisons. You point out that without the sugar, a lot of the packaged foods we eat would make us nauseous.

That’s right. I have nothing against sugar in a good environment. If you have a delicious handmade whole-grain vegan cake, the sugar is very nice. Or some berries with a little extra sugar, and you eat them mindfully—this is excellent. But what happens in the supermarket is a lot of cheap stuff that’s disguised with a lot of sugar, salt, and cheap fat. It’s a catastrophe. And the people don’t know it. They buy it because it’s addictive. Without the added sugar, people wouldn’t touch it.

You write that fruit is the easiest thing to digest.

Yes. Fruit wants to be eaten. The plant wants to spread its seed. What’s interesting is that a lot of people are concerned about fructose, the sugar of fruits. When you add fructose artificially to a food item, a lot of people suffer from intolerance, but there’s a nice study showing even when people eat over 20 pieces of whole fruit a day, you can digest it. As a whole, fruit is perfectly designed by nature.

The other extreme is meat. I hadn’t realized the enormous amount of work that goes into digesting meat.

I think meat is a very sad story. We use animals like machines. It takes an enormous amount of time and energy to produce meat from plants. Then we eat the animals, and it takes an enormous amount of time and work to fragment the meat again. I think it’s a little bit crazy.

A fast is basically allowing your body to rest and recover from all that work.

Yeah, exactly. It’s kind of reset button that’s especially good for people who have bad eating habits or an unhealthy lifestyle. These people feel the most impressive improvements in vitality and wellbeing when they start fasting. For example, we have patients with diabetes, obese people, and they have enlarged livers. After four or five days of fasting, the liver starts to shrink. The liver normalizes, and it happens very fast. Intermittent fasting is also nice. I like it too. But the longer fast is much stronger.

How often should you fast?

In religious traditions, there is typically one fasting period in the year, mostly in the spring. Spring is a good time for fasting. But we know from our patients that under our current lifestyle, it’s better to have at least two periods of fasting a year. It depends on the individual. Theoretically, you could benefit from four or five fasts each year, but you have to find out if this fits with your family life and work life.

What the ideal length of time?

I think the ideal first fasting experience is five days. When you fast for the second time or the third or the fourth time, you can go for seven or eight days. Water fasting is not ideal. We know quite well that water fasting causes muscle loss. So, I recommend a little bit of food, 300 to 500 calories a day.

The main thing is to control the number of calories?

The most important rule is not to go over 500 calories. Those calories also have to be vegan, and they should not have additive sugar. Natural sugar from juice is fine. Staying vegan is very important because any animal protein really disrupts the fasting process. The rest is up to the individual. Some people dislike vegetable juices, so it would not be a good idea to tell them to drink carrot or beetroot juice. Choose calories you want.

You write about the difference between fasting and dieting—that fasting is the only way to lose weight if that’s what you want to do.

Yes. Diets just don’t work. It’s a story of failure. As I wrote in a scientific paper ten years ago, there is no single diet that has a sustainable effect. Diets give you the illusion that you can do something different for a defined period of time and lose weight, but you end up with your old lifestyle—and it gets worse.

The fasting experience changes your mind. You start eating better, and that’s why there is no weight-cycling effect with fasting. You have this experience and then people start to eat differently. And that’s why fasting is not a fad or a diet. It’s a game-changer.

You use fasting for so many diseases. I’m curious about the relationship between fasting and the placebo response.

That’s a fascinating question. Fasting has distinct molecule effects. Medical effects. There’s no doubt about it. But fasting also has mental and emotional effects that you find in placebo research. What’s a tragedy of medicine is that the placebo response was branded as something negative.

The placebo response is our self-healing capacity. It’s the meaning response. When something has meaning for me, my body starts to do what it is capable of doing to heal itself. The very best you can do as a doctor is to maximize any form of self-healing.

Fasting increases a sense of self-efficacy, and that is the most important part of the placebo response. People are empowered. They think, wow, I can do this. I can not eat for five days or for seven days.

As well as long fasts, you also recommend compressing the amount of time in a day that you spend eating. Why is that so important?

That goes back to the beginning of our discussion. It’s because digestion is such a complex task. It’s so much work. We have to give the body a break. For example, hormone systems like the insulin system need a rest. If we snack all the time, the insulin system gets no rest, and eventually goes into resistance—what we call Type 2 diabetes.

Another important hormone is melatonin. Melatonin is very important for sleep and restoration, but it disturbs metabolic pathways. So that’s why we should not eat in the first hour after we awake, because the melatonin is still high. And that’s also why we should not eat three hours before going to sleep. Our body has a rhythm: Three hours before we usually go to bed, melatonin increases.

The melatonin cycle is the first principle of compression: We should not eat for an hour in the morning and three hours before we go to bed. Then we can try to lengthen that period of rest. The more we compress our eating, the more we allow our body to rest and recover. The benefits are significant with 13 hours or 14 hours of rest, 16 hours is better. There’s another process called autophagy. This is the cellular detox, or self-cleansing program, which starts after 12 hours of rest.

Note from the editor: Be sure to consult your doctor before making drastic changes to your diet and exercise!

So constant eating means your body is always working—and never recovering.

Exactly. The benefits also show up in sports. When you fast overnight and go running or cycling before breakfast, you have a better training effect.

Why is it helpful to eat a wide variety of foods?

There is a natural principle called hormesis that most people—including scientists—don’t pay much attention to. But it’s very important. When you have a small dose of a compound, it’s healthy. But when you go much over that dose, it gets toxic.

When you have two cups of coffee, it’s good. A glass of wine is good. But liters of coffee or wine is toxic. Overall, there are many secondary plant substances we call polyphenols and flavonoids that are bioactive and very healthy in small amounts. But when you ingest them in a large amounts, they get toxic. So if you eat a broad range of foodstuff, with different nutrients, different polyphenols, different vitamins, and different proteins, you do the best for your health because then you’ll get everything in a more optimum dosage.

So no matter how healthy any food is, if you eat too much, you have made it unhealthy.

Exactly. This is a law of nature. Most people don’t realize that even radioactivity—in a very small dosage—is healthy. It’s better to have a tiny amount of radioactivity than to have no radioactivity at all. It’s also good to have sunlight, but

it’s not good to have six hours of sunlight. It’s very good to exercise. But it’s not good to do a marathon. Everything gets toxic. And everything needs to rest.


Many religious texts mention intermittent fasting. For example, Luke 18:12 in the Bible reads: “I fast twice a week.” Originally, fasting or partial fasting in Christian culture was done twice a week, in addition to Lent. Wednesday commemorated the betrayal of Jesus, and Friday the crucifixion. But this kind of remembrance and rite of humility disappeared almost completely over the course of the centuries. At my house, however, it was at least partly preserved—on Fridays our family did not eat meat. Instead, we ate only vegetarian dishes or fish (and nothing sweet).

Intermittent fasting is practiced during Ramadan, the fasting month of Islam. Followers of Islam will fast from sunrise to sunset, and can eat and drink only before sunrise and after sundown. But people sometimes overindulge when they’re not fasting. This seems to be a contributing factor to why Ramadan fasting, for example, isn’t as medically successful as other forms of intermittent fasting in many studies.

But overall, fasting during Ramadan does show health benefits. On average, bodyweight drops slightly, and blood lipid values and cholesterol levels improve. Nevertheless, it’s difficult to examine Ramadan fasting scientifically because depending on the geographical location and the time of year, the daily fasting period can vary between nine and twenty hours. In our facility we conducted research into a religious type of fast quite similar to Ramadan fasting, the fasting of the Baha’i religion, which has its origins in Iran. Under the direction of my colleague Daniela Liebscher, we made some interesting discoveries: There was a significant improvement in mood as well as a shift of the circadian rhythm of almost an hour and a half. In other words, fasting can help readjust disrupted circadian rhythms.

Seventh-Day Adventists in Loma Linda, California, form one of the Blue Zones. On average, they live seven to ten years longer than other Americans who don’t belong to this church. The excellent health of the Adventists is mainly due to their vegetarian diet and their healthy lifestyle, but interestingly most of them have their last meal for the day in the afternoon.

This essentially means that they practice TRE (time-restricted eating) with a prolonged night fast. Within the scope of the Adventist Health Study, data on this factor was unfortunately not gathered, but it’s possible that it contributes to the significantly longer life span.

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