For people who are heavily overweight, and suffering from severe or morbid obesity, dieting and exercise will often produce a short-term weight loss and can bring some marked health benefits. Any weight loss is however short-lived and the vast majority of people (between 80% and 95%) will regain their weight, and often put on further weight, relatively quickly. It is no surprise therefore that many morbidly obese individuals turn in the end to the gastric bypass as a lasting solution to their problem. But just how does the gastric bypass promote long-term weight loss?

To understand the mechanics of the gastric bypass we need to start by considering the normal digestive process.

When we eat, food passes initially into the stomach where it is broken down by a strong acid solution. Once the digestive process has been completed in the stomach, food moves into the duodenum, which is the first part of the small intestine, and bile and pancreatic juice is added to the mix to continue the process of digestion. It is here in the duodenum that iron and calcium are absorbed into the body.

Food then continues on down the small intestine, which is almost 20 feet in length, passing first through the jejunum and then through the ileum and it is here that the body extracts the bulk of the calories and nutrients contained in the food that we eat. Finally, any food particles that cannot be digested are passed into the large intestine where they are stored until they are passed out of the body.

We gain weight because the food that we eat contains more calories than we need to support the level of activity within the body and so the body, having burnt up the calories that it needs, stores any left-over calories as fat which is dispersed throughout the body.

Gastric bypass works by altering the body's digestive process in one of two ways.

One form of gastric bypass (referred to as restrictive surgery) physically restricts the quantity of food that we can eat and so not only stops us from consuming more calories than the body needs but reduces our intake to fewer calories than are necessary and so forces the body to start burning off the reserves that it has laid down as fat.

The second form of gastric bypass (referred to as malabsorptive surgery) does not restrict the quantity of food that we can eat but creates a new passage for that food so that a substantial proportion of the small intestine is bypassed and the body is able to extract only a small number of calories. Once again this forces the body to dig into its fat reserves.

In many cases gastric bypass operations are in fact a combination of these two forms and will both restrict the intake of food and reduce adsorption by re-routing the food past much of the small intestine.

There are many variations of the gastric bypass and each has its advantages as well as its disadvantages. Some forms will be more suited to one individual than to another and in other cases it will be very much a matter of personal preference in consultation with your surgeon.

The gastric bypass is a powerful solution to the problem of obesity but it comes at a price and is not without both risk and complication. It is also important to understand that the gastric bypass is not in itself a magic cure for obesity and that you will need to learn to work with your new digestive system by adopting a whole new set of eating habits and a dramatic change to your lifestyle if you are to maintain the weight lost as a result of surgery.

Once the initial and virtually automatic weight loss has been achieved following the gastric bypass it is quite easy to abuse your new digestive system and to start putting the weight back on again.