You extract the goodness in food, pulling all the nutrition out of three days' worth of meals and concentrating it into about a tablespoon of bland, flourlike powder. The flour can be mixed with liquid and drunk or baked into elven bread. Foyson used in this way still imparts all the nutritional value of the original food, for the amount consumed. The original food appears unchanged and though it's still filling, it has no nutritional value. Someone eating nothing but foyson-free food will eventually starve.