How Weight Loss Surgery Works
Figure 1. The Normal Food Digestion System
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After chewing, food passes through the esophagus to the stomach, whose stomach acids break it into smaller particles. It then passes into the small intestine where it's nutrients are ingested. First, in the duodenum, calcium, iron and a few vitamins are absorbed. Next, in the jejumum and ileum, the remaining (majority) of food nutrients and calories are absorbed. The indigestible food remnants (mainly fiber) continue through to the large intestine and are duly excreted.
Smaller Appetite and Fewer Calories
Weight loss surgery works by reducing appetite and calorie-intake. During gastric surgery, the stomach-size is greatly reduced. This reduces appetite significantly. Also, in some stomach surgery procedures, part of the small intestine is "bypassed" to reduce the number of calories (and nutrients) that can be absorbed.
Gastric Banding or Gastric Stapling Surgery
This kind of "restrictive" bariatric surgery uses a gastric band/ring or staples to reduce stomach size. It makes no attempt to alter the anatomy of the digestive tract by (eg) bypassing the small intestine. This kind of bariatric procedure produces less weight loss.
Gastric or Stomach Bypass
This type of weight loss surgical operation shrinks the size of the stomach AND bypasses some (or most) of the early section of the small intestine (duodenum). The bypass causes less food (therefore calories and nutrients) to be absorbed. Hence these operations are called "malabsorptive". This kind of bariatric procedure produces greater weight loss.
Post-Operative Patient Compliance Essential
Neither restrictive nor malabsorptive procedures can be successful unless patients follow the dietary and exercise guidelines issued to them by their surgeon.
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