The term gastric bypass surgery is used somewhat loosely these days and encompasses both true bypass operations like the Roux En Y and increasingly popular restrictive forms of weight loss surgery like gastric banding. Although both have a part to play in curing obesity, bypass surgery takes full advantage of the body’s digestive system to affect weight loss and, in order to appreciate just how gastric bypass surgery works, it is necessary for us have an understanding of the digestive system.
Digestion starts as soon as you begin eating when, as food is chewed in your mouth, saliva, containing the digestive enzyme amylase, mixes with your food and begins to break down carbohydrates. It may not appear this is an important part digestion, but the saliva glands produce approximately 40% of the amylase used in the digestive process and so it is essential to chew your food well.
Your food is then passed along the esophagus and into the stomach where digestive juices and pepsin are added and muscular contractions mix the food.
Once the food is well mixed it is passed out of the lower end of the stomach through the pylorus, which is a circular muscle that opens and closes rhythmically to control the passage of food from the stomach.
Once it has left the stomach food enters the duodenum, which is about 2 feet long and is the first of three sections which together comprise the small intestine. At this point two other organs come into play – the pancreas and the liver.
The pancreas is mainly known as the organ responsible for producing insulin, but it also produces several digestive enzymes, including lipase, which helps in breaking down fat.
The liver excretes bile, which is a necessary enzyme for the digestion of fat, into the duodenum and also receives nutrients from the duodenum along a series of veins known as the portal veins. The liver is therefore also responsible for processing food.
Having been mixed with several digestive enzymes in the duodenum, food then passes into the jejunum, which is approximately 6 to 8 feet long, and then into the ileum, which is approximately 10 to 12 feet long, where digestion continues and further nutrients are extracted.
As soon as digestion is complete any indigestible waste products are passed into the large bowel where water is absorbed to prevent unnecessary water loss from the body. Waste products remain in the large bowel until they are released from the body.
By bypassing part of the small bowl, gastric bypass surgery prevents the body from absorbing too many calories from the food that is eaten which results in weight loss. It also restricts the absorption of several necessary vitamins and minerals and this is the reason why patients need to take supplements following surgery.