The basis of foie gras production is the ability that some waterfowl have to expand their esophagus and to gain weight, particularly in the liver, in preparation for migration. Wild geese may consume 300 grams of protein and another 800 grams of grasses per day. Farmed geese allowed to graze on carrots adapt to eating 100 grams of protein, but may consume up to 2500 grams of the carrots per day. The increasing amount of feed given prior to force-feeding and during the force-feeding itself cause expansion of the lower part of the esophagus.