Even if we do not know the true energy content of a particular food item, we know that the amount ingested is proportional to the energy intake. At that point,

Even if we do not know the true energy content of a particular food item, we know that the amount ingested is proportional to the energy intake. At that point, we need only a simple bisection search algorithm to find a point which allows weight loss without an excessive (note: not zero) feeling of hunger.