The bypass consists in reducing the volume of the stomach and modifying the food circuit.

The food does not pass any more by the stomach and the higher part of the digestive tract, it goes directly in the average part of the small intestine.

The bypass acts by 4 mechanisms which join :

	A restriction (like gastroplasty)
	A malabsorption (the food is less digested)
	A dumping syndrom (the sweetened food ingestion in large quantity gives a feeling of general faintness and an acceleration of the pulse, this food must thus be taken in small quantity)
	A reduction in the rate of ghrelin,  the hormone of hunger, which involves a disinterest for food (be careful : this mechanism is not effective on the possible compulsions).