One of the most interesting observations of the ninth week came with an unexpected personal best.
On the morning of March 4, fasting blood ketones were 0.9 mmol/L. This represents a stable, moderate level of ketosis, which is a good indicator that the body is already operating in a fat-based energy mode even at baseline.
Breakfast was simple: bacon and eggs made with five eggs, accompanied by butter coffee with glycine. No carbohydrates were included in the meal. There was no mid-morning fueling, no extra energy top-up, and no carbohydrate loading of any kind.
Shortly afterward, the run began.
During the run, a new 10 km personal best was set: 47 minutes and 22 seconds. Average pace was 4:44 min/km, with an average heart rate of 158 bpm. The heart rate curve was remarkably stable, showing almost no fluctuation for the majority of the effort. There was no noticeable heart rate drift, and no sudden performance drop-off toward the end.
Energy sensation remained steady right through to the finish. There was none of the abrupt fatigue or energy crash that I used to experience frequently when relying on carbohydrate-based fueling.
Lunch consisted of 400 grams of steak, followed again by butter coffee with glycine.
By the afternoon, ketone levels had dropped to 0.4 mmol/L.
At first glance, this decrease might seem contradictory. The classic interpretation is that higher blood ketone levels mean “better ketosis.” However, sports physiology observations tell a different story.
During more intense efforts, a significant portion of ketone bodies is used up in the muscles and nervous system. When the body is efficiently utilizing this fuel, the measured blood concentration often falls. This does not indicate a metabolic “shutdown”—quite the opposite: it shows that ketones are not accumulating but are being converted into energy.
In other words: fewer ketones are measurable in the blood because the body has burned them.
This is one of the characteristic patterns of adapted sports ketosis. Performance does not depend on high blood ketone levels, but rather on how efficiently the body can utilize available fatty acids and ketone bodies.
The March 4 run was therefore not just a new personal best.
It was yet another confirmation that fat-based metabolism works reliably not only over long durations but can also sustain performance at higher intensities.