Exogenous ketones

What are ketones?

Ketones are produced when our body lacks carbohydrates. Our liver produces small energy carriers from body fat, the ketones (also called ketone bodies). During prolonged food deprivation, such as during a fasting cure, the ketones supply our brain with energy. Our brain is usually not able to directly utilize fatty acids, since the majority of fatty acids from the blood do not reach the brain via the protective blood-brain barrier (exceptions are MCTs = medium chain triglycerides, medium-chain fatty acids). Our brain usually feeds on glucose, i.e. dextrose. If we don’t eat anything or don’t eat carbohydrates for a long time, our brain can only be supplied by ketones, while the rest of the body can use its own body fat or dietary fat from the blood. The ketones produced by the body are also called endogenous ketones. In contrast, ketones that are produced outside the body (by different processes) are called exogenous ketones.

Exogenous ketones have been around for a few decades. In the beginning, the production cost a fortune, which is why exogenous ketones were only used in space travel, military and well-off research institutions. Medicine has been using exogenous ketones for years now. They are mainly used for epilepsy or mental disorders such as anxiety disorders or depression. Taking ketones leads to positive metabolic changes such as improved mitochondrial function (including better fat burning) and anti-inflammatory processes. Animal experiments have shown a reduction in blood sugar levels and ongoing studies suggest that ketones can help fight obesity, which could make them interesting for metabolic disorders such as type 2 diabetes.

Ketones in sports

Since the Tour de France 2019, one hears and reads more and more about exogenous ketones in sports. Ketones are present there as food supplements. These small energy sources improve fat burning in the long term and conserve carbohydrate reserves during sporting exertion, which is particularly desirable during long mountain stages. The insulin sensitivity and regenerative ability of the athletes is increased. Ketones act as a kind of signal molecule and trigger many positive metabolic changes in the body and have an influence on epigenetics.

During heavy physical exertion or when the carbohydrate reserves in the muscles and liver are running low, our body begins to produce the first ketones. Even in the morning after getting up, when the liver stores are exhausted, the first ketones could be produced. There are only a few ketones that cannot be compared to the high production during a fasting cure or a low-carbohydrate diet (ketogenic diet). For the body of sportsmen and women, however, a ketone body is often nothing new, which is why athletes feel a faster effect when taking exogenous ketones. Transport molecules that transport the ketones into the cells of muscles and the brain already exist because the athlete’s body already uses the ketones produced and because certain transporters, which are also responsible for the transport of lactate, are regularly required during sport.

One calorie is not one calorie

One calorie is defined as the energy required to heat one gram of water by one degree Celsius. To determine the calorie content of food, a so-called bomb calorimeter is usually used. This is used to determine the calorific value of a substance or food by burning it at a certain oxygen pressure. It is also possible to determine the calorie content of a piece of newspaper. However, nobody seriously believes that a lot of energy reaches the body when consuming newsprint. Not everything we put in our mouth can be converted into energy by our body. Whether an apple, a jelly bear or a stone is eaten, more or less of it is excreted digested or undigested. It is the same with ketones. The body must be able to use the energy contained in the ketone molecules. Not all ketones are the same.

Experience exogenous ketones as a food supplement

Three different ketones are produced in the body, one of which is more or less a kind of waste product, acetone. Acetone is a ketone, but it can hardly be used by our body and is exhaled or excreted through the urine. Acetone is used as a solvent and nobody would think of using it. It is the same with ketones as with alcohols, the term is derived from the molecular structure of the substance. Besides acetone, two other ketones are produced in our body. The two other ketones that are naturally produced in the body are acetoacetate and beta-hydroxybutyrate. Especially the last mentioned beta-hydroxybutyrate, BHB for short, is a good energy supplier for the body. BHB occurs in two forms (isomerism). A left-turning form and a right-turning form (keyword polarization direction of light). Imagine the two forms like the shapes of gloves. The left glove resembles the right glove, but only the left glove fits the left hand and vice versa. In the human body the right-turning form D-BHB is almost exclusively created. For my test I use a product 100% D-BHBs.

Interval fasting – My first experiences

The ketones tested by me are produced naturally by fermentation (vegan). Chemically it is beta-hydroxybutyrate, which also occurs in the human body. I have tested the ketones in the morning before breakfast. With the ketones the classical intermittent fasting (interval fasting) is supported. Ketones do not increase the insulin level. Hunger hormones such as ghrelin are downregulated, so that a gnawing feeling of hunger does not occur. I have tested the ketones especially in the morning training. I train regularly on an empty stomach. The concept of sobriety training in the narrower sense would have to be examined and discussed more closely, which would go too far at this point. My carbohydrate stores are more or less filled. My body has learned to manage the stored glucose. However, as soon as I have hardly any carbohydrates stored in my muscles, it is of course not without danger to go on a sometimes more intensive bike ride. Hypoglycaemia can be fatal in traffic. However, since I don’t want to increase my insulin level during the session with gels or bars to continue burning fat, I filled my water bottle with ketones. The tested ketones are in powder form and are dissolved in water. Through the ketones I was able to significantly reduce my hunger feeling during the units, sometimes it disappeared completely. Once I started with a strong growl in my stomach as well as legs and head without energy. Drinking the ketones made this disappear after some time. Here I noticed a clear effect. An increase in performance due to the intake has not occurred so far. My performance (Watt) was as usual. From other experience reports, however, it is said that some effects only become really noticeable after a longer intake. I will continue to test.


In the first weeks of the test phase, I took the ketones in the morning on an empty stomach for training. Without breakfast I went for two hours on a flat 60 km bike. Sometimes there were 16 hours between dinner and the bike ride, the distance of the classic interval fasting. I am used to sober training, but with intensive units there is the danger of slipping into hypoglycaemia. With higher intensities the muscles need glucose and can make the sugar to the brain virtually deny. By taking the ketones an insulin-independent energy source is available. I noticed this immediately on every ride. With the intake of the ketones my hunger disappeared immediately. I was able to finish my training rides with sustained performance and in some cases I was also able to increase my performance.

My “extreme test” took place late in the morning. I had not eaten anything for 14 hours before my ride. The dinner the evening before was a normal mixed diet. For the test I had done a flat 50 kilometer track. I was already hungry before the exit. I filled my ketones into the water bottles and drove off, taking the first sip. After a minute I changed to “race pace”, which I kept almost to the end. I rode the entire distance – as far as the traffic allowed – just below the threshold power in the upper endurance range. Only at intersections or behind cars, trucks and tractors, I had to adjust my speed at short notice. During my ride the feeling of hunger disappeared completely. I regularly took a sip. In the end I had completed the 50 kilometers with a 35.8km/h average, sober without preparation like restdays or carbloading in the previous days.

In short: 50 kilometers at 35.8 km/h, sober (14 hours without food), no preparation (no carboloading, over 3 hours of training the day before), riding an ordinary roadbike and traffic, no race track. Strava-activity

My conclusion: the ketones I tested arrived in my body and gave a noticeable energy boost. Without ketones, this performance would not have been available soberly. In my opinion, the ketones are suitable for direct use in competitions or training. However, since ketones are supposed to have further and more long-term positive effects, I will continue testing.


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