A Self Experiment with Nutritional Ketosis

April 8, 2013

Last year I started a nutritional self experiment. Almost half a year later I think it’s time to share my experiences. Admittedly, I’m going on a bit of a tangent here compared to what I usually want to write about. But this journey still has its roots in something which is not so unrelated…

It all started when I listened to the first episode of the “Over the sugar hill” podcasts with Steve Gibson and Leo Laporte. Normally, Steve Gibson does the weekly Security Now podcast on twit.tv where he talks in depth about interesting security related topics. I highly recommend his podcast by the way!

Anyway, Steve started to eat a very low carbohydrate diet and shared his experiences on the before mentioned special episode. As he does with all his topics, he had thoroughly researched the field and approached this experiment with a curious scientific mind. I was immediately interested, but it still took me a while until I convinced myself to give it a try.

The general idea was not totally new to me. I had read about the Paleo diet before and I even tried it myself twice. I failed miserably though. Both times I didn’t make it past the first 72 hours. The cravings for bread and pasta just were way stronger than my determination to continue. But I noticed during these short intervals that my digestive system generally liked this way of eating.

The Very Low Carbohydrate Diet

Before I listened to Steve’s podcasts I wasn’t aware of the fact that there is a decisive difference between the various interpretations of a Paleo diet, and what can be described most generically as a very low carbohydrate diet. With a Paleo diet you still consume a significant amount of carbohydrates in the form of all kinds of fruits, juices, nuts, pumpkin and so on. A very low carbohydrate diet restricts carbohydrate intake to below 50 grams per day. That means you have to basically avoid all foods which have any significant amount of carbohydrates. The 50 grams will creep in anyway.

Once you cross this threshold of daily carbohydrate intake (there are of course quite some inter-individual differences) your body goes through a major change in metabolism: the liver starts to produce ketone bodies. The interesting thing about ketones is that the brain can metabolize them.

The brain can use glucose and ketones as energy supply. If you eat regular amounts of carbohydrates, the ketone level in the blood is very low and the brain relies on sugar as energy source. Therefore it is very dependent on food intake, because the blood sugar level goes up and down during the day dependent on what you eat. These cravings for food, the lack of concentration and energy after a meal – that’s your brain complaining about a too low blood sugar level.

Once the body starts to produce ketones, you basically free your brain from its energy dependency on sugar, and therefore of all the cravings and ups and downs you’re normally experiencing. Furthermore your skeletal muscles adapt by primarily using fatty acids instead of glucose as fuel. If you want to know more about this process, Steve Gibson has nice summaries and links to further resources on his site.

But now back to my personal story.

The First Act

After two more episodes of Steve’s sugar hill podcasts and reading the book “The Art and Science of Low Carbohydrate Living” by Steven Phinney I was ready to give it a shot. In the interest of full disclosure I have to say that there was no acute reason for me to change my nutrition. I have never struggled to maintain my body weight in my entire life, I didn’t have any complaints about my digestive system and enjoyed the food I was eating. I wanted to try it out of pure curiosity.

I started to cut out all the carbohydrates from my diet in late October 2012. The first days went by and surprisingly I didn’t have any problems to maintain this way of eating, contrary to my previous attempts of eating the Paleo way. I largely attribute this to the greatly reduced sugar intake (i.e. less ups and downs in the blood sugar level) as well as the consistent replacement of energy from carbohydrates by fat.

Yes, you have to eat much more fat than what you’re used to. Basically you have to take every opportunity you can get to prepare food with more fat than usual. We can only digest a very limited amount of protein, so the overall ratio of energy sources has to be in the range of 80% fats and 20% proteins. To achieve this you have to radically change your shopping and cooking habits. Eating out becomes a bit more difficult. You can mostly refrain from eating the carbohydrate rich parts of the food, but that also means that you are lacking the energy contained in the potatoes, pasta, rice, etc. without substituting it by fat.

A few days into my experiment I decided to get a blood ketone test device in order to be able to track my body’s reaction better. It’s a lot of finger poking, but I got used to it quickly and having this kind of data available is kind of cool. The following graph shows the daily ketone levels during my first period of very low carbohydrate eating.

While eating a normal carbohydrate rich diet your blood ketone level is pretty much zero. As you can see in the first part of the graph my ketone levels went crazy during the first two weeks, hitting almost 4 mmol/L. This actually indicates you’re body struggling with the nutritional change. Your muscles still are conditioned to use glucose as primary fuel, so the liver starts to synthesize a lot of glucose, which produces ketones as a byproduct. After approximately two weeks the values settled down below 1 mmol/L for the most part.

During this initial phase my physical performance was going down significantly. I still could maintain low exercise intensities for extended periods of time. But as soon as I started to increase intensity I basically hit a wall. Heavy legs, burning muscles – as if I just completed a hard workout, but I actually just tried to start it. After two weeks my capacity for higher intensity exercise started to recover and my breathing rhythm settled at a lower frequency than before. However, I still feel that this kind of diet will put a cap on your performance if you want to train regularly at high intensities.

I became used to the new eating habits very quickly, and I actually really enjoyed it. It forces you to be more creative with your cooking. Food preparation took a bigger role in my daily life than before, and I enjoyed it as part of this project.

About seven weeks into the diet my digestive system started to feel a bit stressed from time to time. I noticed that this was always a direct reaction to eating, and it went away one to two hours later. The complaints became more severe over christmas and new year, and I was almost ready to start eating carbohydrates again. Beginning of January I experimented with the sugar replacement Xylitol, which resulted in an immediate drop of my ketone level to 0.2 mmol/L. I noticed that my digestion pains got better though.

A week later I finally threw in the towel and started to eat carbohydrates again, as you can see with the ketone level flatlining at 0.1 mmol/L. It only took a few days until the digestion problems completely disappeared.

I was disappointed, because I actually really liked the way of eating and before the digestion problems started I was feeling great. All cravings for late night sweets and a regular tendency to keep eating although I was already full practically disappeared during this experiment. Also, the sensation of hunger was totally different while being in ketosis. It was more an informative sensation from the stomach that there is enough space for some more food, rather than the brain demanding sugar rather rudly…

The Second Act

Beginning of February I decided to give the diet another try. I was curious if it would go the same way as the first time and if the digestion problems I ran into previously would reappear. I noticed early on that my stomach started to feel bad again every time I was eating eggs. Cutting out eggs from my diet the stomach problems went away and I haven’t had any complaints until now, almost ten weeks later.

However, my body’s reaction to the diet was very different this time around, although I was eating the same way as during my first low carb period. My body seemingly still remembered the metabolic state of ketosis well enough, so that there was almost no adaptation period. The ketone values started to rise moderately and stayed pretty much constant ever since at around 0.2 to 0.4 mmol/L, much lower and much more constant than the first time. My body seems to have settled in a steady state.

Recently I started to experiment with handling the diet a bit looser. It turns out that for me an occasional piece of cake or other high carbohydrate foods don’t throw me out of my steady state very much. The ketone levels might drop down for one day, but they come right up to the previous level the next day.


I really like the very low carbohydrate way of eating. I don’t need it to control my body weight, blood sugar, allergies or other medical conditions. But my regulation of food intake feels much more natural this way. I never feel stuffed, I make far less stupid eating decisions and I just have a more constant concentration level throughout the day.

I never could have imagined before to live without pasta, rice, potatoes, and all the nice things you can make out of flour. I really liked the mediterranean kitchen. But being in ketosis for a little more than four month with a short interruption, I have to say I don’t miss anything. And the ability to maintain this steady state despite occasional carbohydrate intake makes it even better.