Gastric bypass has been around for well over fifty years now and, while it does carry risks the majority of patients are very happy with the outcome and enjoy a a dramatically improved standard of living. But there is a price to to be paid and you will have to lead a very different lifestyle following surgery which could be very hard unless you are prepared for the change.

Some of the post-operative changes are obvious as the principle behind gastric bypass surgery is to drastically reduce the size of your stomach and restrict the amount of food which you can eat. This means that the days of sitting down to a big meal are gone.

However other consequences of surgery are less obvious.

As an example, even in small quantities your days of eating foods which are high in fat or sugar are also over. The consequences of eating such foods can be extremely unpleasant as rapid absorption in your now shortened digestive tract can produce very nasty feelings of faintness.

You will also find that the dramatic change in your pattern of eating leaves you very short of water so that you need to adjust to drinking small amounts of water during the day to avoid becoming dehydrated.

This is all very well but just what can you expect from obesity surgery when it comes to weight loss?

Results will of course vary from one person to the next but it is important to start by understanding just how post-operative weight loss is measured.

The starting point is to calculate just how much excess weight you are carrying and this means working out your ideal weight. Working in pounds, for a man this is 106 plus 6 times your height in inches minus 60. For instance, for a man 5ft 10ins tall the ideal weight will be (106 + [6 x (70 – 60)]) which works out at 166 pounds. In the case of a woman the principle is exactly the same but this time a women's ideal weight is 100 plus 5 times her height in inches minus 60.

Therefore, taking the example of our man above and give him a weight of 366 pounds before surgery then he is carrying 200 pounds in excess weight. From this starting point we will measure weight loss in terms of the percentage of excess weight lost over time. Thus, if at the end of 6 months his weight has fallen by 100 pounds then his weight loss will be 50 percent.

In the majority of cases you can expect to lose about 50 percent of your excess weight within in the 6 months after surgery climbing to about 70 percent one year after surgery and to possibly 80 percent at the end of 2 years. For the majority of patients however weight loss will cease after 2 years and some long-term weight gain will appear. Long-term weight gain is typically around 10 to 15 percent of your excess weight.

Once again, generally speaking, if you are grossly overweight you will lose a greater percentage of your excess weight (possibly as much as 90 or 95 percent) while if you are less overweight you may lose as little as 60 percent in the 2 years following surgery.

You will almost certainly not lose 100 percent of your excess weight and are not going to get to your ideal weight through surgery. Consequently, it is sometimes said that weight loss surgery is not a complete success. Nevertheless the overwhelming majority of patients would not agree with this and will tell you that the improvement in their quality of life is simply incredible.