Because the growth process of the goose, are inseparable from the water, itself needs a lot of heat energy to maintain will, in the process of growth, need a lot of nutrients to generate feathers.

Because the goose's diet is mostly grass and other water creatures, the body accumulates very little fat.

Because geese often live in the water, they are often coated with fat, and they consume a lot of calories (to combat the cold in the water), which results in a large amount of body fat being consumed, so they have very little fat.

But the artificial rearing of geese, in order to obtain foie gras, and deliberately take the fattening is another matter.