My Fourth Fast: Update on Five-Day Fasting for Health and Mental Performance

I broke the fast with almonds and cashews.

It is Saturday, June 30, 9:30 am. I just broke my fast with some cashew nuts and almonds.

This was my fourth fast, and it was a bit harder than the previous one. My hunger never completely subsided. I changed a few things that may have contributed to this experience. For more on this, please see below.

But – this fast also made me appreciate the value of food again.

I still went to coffee shops to do some reading and drink black coffee. When friends ordered food or a takeout, I felt they were so lucky they could have nice looking and clean food and eat it.

It doesn’t feel nice to be hungry and not to be able to eat when food is plenty.

Feeling hunger, I felt connected with people who don’t get enough to eat.

I had to go to bed without food for 5 nights. But I knew that after 5 days I was going to have great meals again.

I have the cash to go to the supermarket and buy stuff to my heart’s content.  I was already planning the great meals I was going to have.

Other people don’t have enough resources. They often go to bed hungry without knowing when they will have a satisfying meal.

They might only have a bowl of instant noodles with some cheap oil and lots of flavor enhancers. Not too bad if eaten once in a while, but while the noodles are high on carbs, they are low on protein and contain almost no nutrients.

But then, a bag only costs 50 cents. Mind you, the almonds and cashew nuts I broke my fast with cost more than that.

I sometimes eat these noodles too, because they taste good. Or a cheap fried rice dish. But then I remind myself that apart from energy there isn’t much in there and go and get some real food.

It might be a roast with potatoes and nicely grilled vegetables. Or I might go for Sashimi or Oysters.

Some people only have a dollar a day to spend on food. If they have children, the food goes to the kids first.

Today I pity them. Sometimes, I forget.

I am a lucky bastard to have a credit card and a bank account with money to buy nutritious food.

Giving someone good food to eat is sometimes better than money. The person gets to taste the happiness that comes with eating a hearty meal. The food pulls them right out of their hunger and feeling of dissatisfaction.

Why do I fast?

Disclaimer: Consult with your doctor before you try fasting. Fasting isn’t for everyone. This is particularly important if you are taking medication. Among other things, blood sugar levels and blood pressure may be very different in a fasted state.

I fast for health and mental and physical performance and, I have to admit, for weight loss when the scale keeps slowly moving up.

About 1.5 years ago, I was becoming increasingly carbohydrate intolerant. I would eat rice, noodles, or even only an apple, and perhaps half an hour later start feeling sick and slightly depressed. Through mental exercises and optimism I kept everything in order, but I wanted to go back to my former self.

I felt best when I didn’t eat.

Here I got the first hint that not eating, i.e., fasting for a couple of days might be a good idea.

I frequently checked my blood sugar, and it was still in the normal range, but over the years it was slowly creeping up, as was my weight.

Well, after coping with my carb intolerance for a few weeks more, I took the plunge and stopped eating for three days. Then a few weeks later I went for a five-day fast.

These two fasts did the trick. I lost quite a bit of weight and, more importantly, I could eat again and feel well after eating.

I went back to eating normal. I made some changes to when I eat what, and I also cooked more at home, but I wasn’t dieting or something.

Still, I was able to go for much longer without food without running low on energy or feeling grumpy.

This helped a lot when reading, writing, or doing other mental work. I also felt more at ease and happy throughout the day.

My brain just had a much better and more consistent energy supply. Often I would only notice by checking my watch that it was time to eat.

It’s pretty cool when you don’t always have to chew brain-foods and still perform well.

Now, I do like eating too, and I like drinking beer. When feasting too much, my weight does slowly go up again. Perhaps not helping either is that I go to bed at different times and often sleep too little.

So for the time being, I have decided that I will have to fast from time to time to keep everything in a balance.

How do currently I fast?

Note: For more info and the reasoning behind this regime, please check my post Fasting for Metabolic Health.

I make a regular Sunday dinner my last meal.

Until the following Saturday morning, I don’t eat. This makes it a 5.5-day fast.

I drink plenty of water, tea, two cans of club soda, and coffee.

I add sea salt and lite salt (sodium + potassium) to my water. Previously, I added about 6 to 7 grams, but this time maybe 1.

During the course of a day, I spice my water up with two table spoons of apple cider vinegar and some lime.

I add up to 10 grams of butter or MCT oil to my coffee, up to three times per day. This time I cut it down to one time.

I supplement magnesium citrate (2 x 160 mg magnesium).

I go about my day as usual, but substitute walks for more strenuous exercise.

I still go to coffee shops but will only have black, unsweetened coffee.

What data do I track?

I measure blood glucose in the morning, at lunch and in the early evening.

From day two on, I also measure blood ketones at the same times. (see below)

I weigh myself, measure my waist, and take my blood pressure, pulse, and body temperature every morning.

What happens when I fast?

I get hungry. 😎

In a nutshell, the body changes from mostly relying on sugar for energy to burning fat. Most of us have ample fat stores that would in principle allow us to live for many days without consuming energy.

During normal eating times, the issue is getting energy from fat released. Not so when fasting.

If I just keep properly hydrated, I should be able to keep going for a month.  (I don’t want to fast for too long though. I would be concerned of losing muscle mass.)

We also have a sugar store (glycogen store=glucose molecules chained together) in our liver and our muscles. The glycogen store (ca. 100 g) in the liver provides ca. 400 kcal of energy. More glycogen, about 400 g, is stored in our skeletal muscles, providing another 1600 kcal.

Muscle glycogen can only be used by the muscles, while liver glycogen can used for various purposes, in particular to power the brain.

In a sedentary state, the brain consumes about 60% of the blood glucose made available.

Unlike other tissue, the brain cannot directly use fat as an alternative fuel.

As we fast, our glycogen stores become largely depleted, but the body can use protein and fat to make glucose.

After about two days or so, the liver also starts producing an alternative fuel, ketones from fat. Ketones can be used by almost all cells in our body, including our brain. This reduces our reliance on glucose.

You can directly measure blood glucose and blood ketones using a dual-function glucose meter. During the first two to three days, glucose goes down and ketones go up.

What also goes down during fasting is insulin. Insulin is a fat storage hormone; high insulin keeps fat from being released.

Since I have ample fat in storage, after a slightly difficult transition period of three days, I should be able to rely mostly on fat for my energy needs.

How did this fast go compared to my previous one?

So this has been my fourth fast.

It was a bit harder than the previous one, perhaps more comparable to the first fast.

The first three days were pretty much like before, with day one being a more or less smooth ride. I didn’t feel very hungry and my energy was high.

Day two, I was getting hungry, but energy was still high. Day three was the hardest with hunger coming and going and also less energy. My brain felt sluggish, but I wasn’t getting physically weak.

I expected days four and five to be smooth sailing. But, unlike before, this time I still felt hungry and at times even grumpy.

I was getting enough energy to move around, but had to force myself much more to read or write. So I wasn’t exactly productive.

Here are the charts tracking glucose and ketones during this fast and the previous one. Please note that this time I fasted for 5.5 days (as planned) while during the previous one I went for 6.5 days.

Fast June 2018: Glucose and Ketones

Fast March 2018: Glucose and Ketones

Generally the pattern is the same. However this time, I started with a lower glucose value and glucose initially fell faster. On day 5, glucose was somewhat reluctant to come down to 3 mmol/l.

These low blood sugar readings (min. was 58 mg/dl = 3.2 mmol/l) might surprise you, but I didn’t feel hypoglycemic or something. The ketones made up for the shortfall in glucose.

To learn more about how I tracked glucose and ketones, please see my previous fasting post.

My resting heart rate dropped rapidly from 68 to 63 bpm and stayed there for the duration of the fast.

In contrast, in March, it dropped from 72 to 70 bpm, which was in line with prior variations.

During the last three months, I have been exercising a lot more compared to the beginning of the year. This might explain this difference.

I keep track of my heart rate and sleep with a Fitbit Charge 2.

Resting heart rate

My sleep was better this time. Unlike in March, I had no issues falling asleep, and I got more deep sleep. I still woke up much more than usual.

My weight went down from 97.5 to 93 kg (I am 1.9 m tall). Obviously most of this is water weight.

I broke the fast on June 30, 9:30 am, while for the previous one it was March 11, 11:15 am.

What did I do different this time?

As detailed in my previous fasting post, I usually eat about 6 to 7 grams of salt a day to replenish electrolytes, about half normal sea salt and half lite salt (contains sodium and potassium).

This time, I didn’t feel like doing it. I only added perhaps 1 gram to my water during the day.

My blood pressure held up better than last time, so I thought I’d skip the large salt intake. It just doesn’t taste very delicious.

During my previous fast, I also allowed myself about 100 kcal of fat (half butter and half MCT oil) per cup of coffee, totaling about 300 kcal per day.

This time, I only did this on days one and two. From day three on, I only added about 10 grams of butter to my morning coffee. I just didn’t feel like consuming fat.

I drank two to three cups of coffee plus ample water, albeit less than before, during the day. I also had two cans of Club Soda, which also contain salt.

On day four, I accidentally had a few sips of ice coffee with sugar; I asked for iced Americano without sugar, but the café added some anyway. The sip felt good, but I returned the coffee right away. In the evening I could see that my blood ketones had gone down. I was still (or again) in solid ketosis though.

Other supplements I used:

  • Twice a day a capsule of magnesium citrate, for a total of 320 mg of magnesium a day.
  • Twice a day a table spoon of apple cider vinegar added to 300 ml water.
  • Half a lime in water.

This time, I didn’t get any lower back pains, and also no excessive stomach growls.

I did get some unpleasant shoulder pains though. I think they stem from recent workouts, but it felt as if fasting was aggravating the problem.

Today is Tuesday, the fourth day after I completing the fast, and the shoulder pain is mostly gone.

Breaking the fast

Owing to the advice in Dr. Jason Fung’s guide to fasting, I broke the fast with nuts, 10 grams of almonds and 10 grams of cashews.

Then about an hour later I prepared a vegetable and protein shake. I lightly cooked the vegetables and pan-fried the pork chops in olive oil.

I let everything cool down and then put it in the blender with about 400 ml water and some ground pepper.

vegetable-protein shake receipe

Breaking the fast with some fresh veggies and meat.

First vegetable shake

Vegetable-protein shake macronutrients

Breaking the fast this way worked well. I had no digestive issues.

The first shake was a bit too much. An empty stomach can make you greedy.

Next time, I will aim for a 400 kcal shake (2/3 of this one).

For dinner, I had chicken breast with vegetables and potatoes.


While this fast proved to be slightly more challenging, it was still very manageable.

I hope to get the same mental and physical stamina benefits I got from the previous ones.

For future fasts, I will again up the salt to 5 to 6 grams.

I am also going to research what kind of benefits more frequent two-day fasts might provide.

Going for 5+ days without food isn’t exactly my most favorite past time. It gets pretty boring actually.

Despite this, I am glad I did it again.

Apart from a much longer lasting ketogenic diet, fasting has so far been the most effective tool for me for improving my metabolism and stamina. And, what is not to like about shedding some excess pounds?

I feel lucky to have access to good food whenever I so desire.

If you need more detailed information on my experience with fasting and all tools and resources I use, please check my first experience report on fasting.

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