Hi Louisa,
Simple (lay person's explanation of differences between a bypass and a sleeve).
1. RNY Bypass (Roux-en-Y gastric bypass)
A small pouch is created using the top part of the stomach. This is then re-routed to the lower intestine. This therefore bypasses a large section of the intestine.
Weight loss is caused through 2 effects: (1) calorie restriction due to the small size of the pouch, and (2) malabsorption (the bypassed section of the stomach would have been able to absorb more calories and micro-nutrients) -- this is why keeping up with vitamin and mineral supplements (especially Iron, Calcium and Vitamin B12) is so vital post-bypass.
2. SLEEVE (vertical sleeve gastrectomy)
In this operation 80% of the stomach is removed. The part of the stomach which is removed (the back part and most of the fundus) contains the most ghrelin producing cells. Ghrelin is a hormone which controls hunger and appetite, so removing a large amount of the stomach's capacity to produce ghrelin helps significantly in reducing hunger.
Weight loss for sleeve patients is achieved primarily through (1) restriction, having a very narrow tubular stomach (smaller than in the picture -- usually only about 100 ml / 4 oz capacity at the time of the operation), and slightly (2) hormonal changes and lessening of the hunger hormone.
There is no malabsorption with the sleeve -- everything consumed will be absorbed (i.e. calories and all vitamins and minerals).
SLEEVE -- does not affect the lower intestines (an advantage for people who have had previous intestinal problems) and retains the pyloric valve -- this is a valve at the base of the stomach which (1) shuts off and keeps food inside immediately after ingesting, and (2) then slowly releases food into the intestine once the digestive juices have done their work.
Will be back in 2 more tickety boos with a few more links.
