Red meats
after either the gastric bypass, or the gastric banding, red meats are not well tolerated, and may cause vomiting. This is purely a mechanical effect – your stomach cannot tell steak from chicken, except that steak is much harder to break down so that it will fit through the small stomach outlet. If the outlet gets plugged, vomiting will result. We advise patients to avoid red meats until their stomach is functioning very well, usually after at least 3 – 4 months.
Sugar
refined sugars and candy consist of many small molecules, which tend to draw fluid into the intestine. After the gastric bypass (not after the gastric banding), a condition called "dumping syndrome" may occur, when sugar is taken on an empty stomach, passes rapidly through the stomach into the intestine, and draws a large amount of fluid into the bowel. The physiology is complicated, but the result is a condition like shock: one turns ghostly pale, breaks out in a profuse sweat, feels butterflies in the stomach, a rapid pulse, and a feeling of prostration. Nause and vomiting, cramps and diarrhea may follow. Most people who have this reaction never try to sneak another candy bar – and we think that’s not such a bad effect, if you’re trying to lose weight.
The problem of dumping is avoided by avoiding sweets, candies, and fruit juices on an empty stomach. Certain dressings, barbecue sauce and mayonnaise may also cause problems, and need to be avoided.
Milk and milk sugar
to digest milk sugar (lactose), our bodies need and enzyme called lactase, which is often in short supply in the lower small intestine. After gastric bypass (not after gastric banding), milk and milk products may not be fully digested. Farther downstream, they are fermented by bacteria, and this causes gas, cramps and diarrhea.
Milk can be treated, to make it tolerable. In the big picture, it’s probably better to avoid it. Many prepared foods (those that come in a box, or frozen entrees) contain milk sugar as an additive. It is important to learn to be a label-reader, or to avoid packaged foods, and especially junk food.