When I started the functional carnivore diet, my goal was not to follow an extreme diet, but to build a consciously structured metabolic strategy. The foundation of my diet consists of whole animal-based foods: meats, eggs, fish, and natural fats. Carbohydrate intake is minimal or practically zero, while I adjust protein intake to the sports load, and the majority of my energy comes from fat.
The goal of this system is not rapid weight loss, but the reprogramming of the body primarily toward fat oxidation. With low carbohydrate intake, insulin levels decrease, glycogen stores gradually become depleted, and the liver begins producing ketone bodies from fatty acids. Among these, beta-hydroxybutyrate not only serves as an energy source but also has anti-inflammatory and nervous-system-stabilizing effects.
In this state, the body no longer relies on external sugar intake but on its own practically unlimited fat reserves. In an ultradistance event this is a huge advantage: energy supply becomes more even, sudden drops disappear, and inflammatory stress decreases.
One of the key elements of the system is maintaining electrolyte balance, especially sodium replenishment. With low insulin levels, the kidneys excrete salt and water at an increased rate, so without proper replenishment heart rate spikes, fatigue, and performance decline would occur. This is why salt played a prominent role throughout fueling.
I consciously started the year with a three-day water fast, which helped quickly shift the body toward fat oxidation: insulin levels decreased, glycogen stores were depleted, and ketone production began. The body responded surprisingly well, without any serious collapse.
After this, I transitioned to a strict carnivore–ketogenic diet with a high fat ratio, while during training I fueled exclusively with water and salt.
In the first weeks, a more difficult phase appeared at the beginning of every run, and then after roughly seven to eight kilometers the system noticeably “switched”. Movement became smoother, heart rate stabilized, and energy supply became even. As the weeks passed, this transition became faster and more predictable.
Ketone measurements did not show extremely high numbers, but they remained within a stable range. After training the ketone level often remained unchanged or slightly increased, which indicated that the body was not accumulating this energy system but using it efficiently. This was the first clear sign of adapted sports ketosis.
Meanwhile, running volume gradually increased, while recovery did not worsen but improved. Back-to-back long runs appeared, with loads of 25–40 kilometers on consecutive days, which the body handled with progressively smaller stress responses. The next day movement remained easy, heart rate smoothed out quickly, and often the second long run even went better.
Mentally, a major change also occurred. The constant need for fueling and energy monitoring disappeared. Runs became calmer and more predictable, and the low points vanished.
By February it became clear to me that the system was no longer operating in an experimental state. The body was not struggling with the new mode of operation but cooperating with it. The load no longer destroys but builds, recovery accelerated, and energy supply became more even.