To Answer your question in full!! Here is the info on RNY:
Roux-en-Y Gastric Bypass (RNY):
There are a number of techniques currently in use for the surgical treatment of morbid obesity. The one currently favored by the New York Bariatrics Surgery team is the Roux-en-Y gastric bypass. This is the most commonly performed weight loss surgery procedure in the United States, being performed about 75% of the time.
This surgery involves creating a small (less than one ounce) vertically oriented stomach pouch, as well as a bypass of most of the stomach and a varying amount of small intestine (see figure). As a result, weight loss is accomplished both by restriction of food and by malabsorption of nutrients. Ingestion of concentrated sugar is also essentially prohibited because doing so results in "dumping." Dumping is a group of unpleasant symptoms that resembles food poisoning (nausea, vomiting, diarrhea, abdominal cramps, flushing, and palpitations) that occurs when simple sugars enter the small intestine without first being properly digested by the stomach. Many people also report diminished appetite after Roux-en-Y gastric bypass, as well as a change in the taste of food. By looking at the diagram of the Roux en Y gastric bypass it may seem intuitive that this configuration interferes with the normal digestion of food. This is so because the digestive enzymes normally produced in the stomach and upper small intestine continue to be made, but do not contact the food that has been ingested until a few feet down the intestine. Hence, the digestion of the food is delayed until it is already part way down the intestine.” These are additional ways the gastric bypass causes weight loss. Following RNY surgery, patients are at risk for developing anemia because of poor absorption of iron and vitamin B12. Therefore, dietary supplementation of these nutrients is required. Poor absorption of calcium may also occur. Thus, calcium supplements must also be taken postoperatively.