Ketones in the blood after three days of low-carb eating are often read as “I’m fat-adapted now.” They are not the same thing. Producing ketones starts within days; using fat efficiently as a primary fuel is a slower renovation — mitochondrial enzymes, transport proteins and muscle fuel preferences adapt over several weeks, sometimes months.
The stubborn early phase feels contradictory: ketones measurable, energy mediocre, workouts flat. That is the transition window — glycogen is low, fat machinery is still ramping up, and the brain is negotiating its fuel mix. Most of the classic “keto flu” lives here, and most of it is electrolytes and patience.
IQFood models this as a curve, not a switch: the engine tracks an estimated fat-adaptation level that climbs with consistent weeks, not consistent days, and it deliberately refuses to jump to conclusions from one good morning reading. Expect the estimate to move slowly. That slowness is honesty.
A useful mental model from the data: week one is chemistry, week three is machinery, week six is habit. If your energy curve still dips hard at week one, nothing is broken — the renovation simply isn’t finished.