“How does a gastric bypass surgery work?”

Google, You Tube or Wikipedia. You need pictures.

Gastric bypass works by reducing the size of your stomach so that you eat less. Also part of your small intestines are bypassed therefore you absorb less of the food that you do eat. So it works by two mechanisms one It causes you to eat less and two you absorb less of the food that you do eat.

Best to directly ask a bariatric surgeon. I would consider banding.

A gastric bypass is a great operation for the right patient. It is a "restrictive" operation where the size of the stomach is decreased. A surgical stapler is used to create a small pouch at the top of the stomach. The small intestine is then re-arranged (or "bypassed") to drain the pouch into the rest of the gastrointestinal tract.

By dividing the stomach, the hormones and nerve signals between your stomach and brain are changed. In addition to physically being unable to eat much food due to the small size of your stomach, the operation decreases your hunger and increases your satiety (sense of fullness).