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Expected Weight Loss After Bariatric Surgery

In the field of weight loss surgery, four standard bariatric procedures help patients lose weight and keep the weight off—the Gastric Band, Gastric Bypass, Gastric Sleeve, and Duodenal Switch. In last week’s blog, we pointed out the critical differences between these procedures and highlighted some risks and benefits of each operation. 

The least invasive bariatric procedure is the Gastric Band, which involves placing a silicone band around the upper part of the stomach. The oldest staple bariatric procedure is the gastric bypass, although the gastric sleeve has gained popularity in recent years due to its perceived simplicity. Yet aside from the bypass and the sleeve, a third staple bariatric procedure is emerging as an effective tool for bariatric patients with a higher body mass index (BMI) known as the duodenal switch. 

All of these weight loss surgery procedures have various degrees of expected weight loss. 

How to Measure Expected Weight Loss

Before we jump into what you want to hear—how much weight you will lose—I want to state that the way we compare weight loss results is as a percentage of excess weight loss (%EWL).

Weight Loss after weight loss surgeryIn other words, if a patient’s starting weight is 200 pounds and their goal weight is 100 pounds, then they are 100 pounds overweight. Therefore, if they lose 100 pounds after surgery, they will have lost 100% of their excess weight; and if they lose 50 pounds, they will have lost 50% of their excess weight. 

To calculate the %EWL you will subtract your starting weight from your current weight, divide that by your excess weight, then multiply that result by 100 to get your percentage. 

Keep in mind that good results from traditional dieting and exercise programs generally tout a success rate of 5% to 10% EWL. 

How Much Weight Will I Lose?

A question I often get asked by bariatric patients is, “how much weight will I lose?”. The short answer is it varies based on several factors, including but not limited to age, genetics, gender, starting weight, and motivation level. 

However, after being in this field for more than ten years, I have observed a few common generalizations. 


Gastric Band Expected Weight Loss

Patients who have the Gastric Band can expect to lose around 35 to 45% of their excess weight. If an individual loses about 40% of their excess weight with the Gastric Band, that is pretty good weight loss. 

However, if the patient loses more than ~40%, the band is likely too tight, and the patient is probably experiencing reflux and not eating in a routine and social way. Often this can result in having to have fluid removed from the band to loosen it, and unfortunately, when this happens, the patient will often regain a significant amount of weight. 

Therefore, we do not often recommend the Gastric Band for our patients due to the unsatisfactory weight loss results. 

Gastric Sleeve and Gastric Bypass Expected Weight Loss

The weight loss results associated with the sleeve and bypass are very similar. Most individuals can expect to lose somewhere between 60 to 75% of their excess weight. 

The patient’s starting body mass index (BMI) will determine how much weight they can expect to lose. Patients with a BMI in the 40s and 50s will lose a significant amount of weight; however, they will lose a smaller percentage of their excess weight. On the contrary, patients who started at a lower weight range (BMI in the 30s and 40s) will often lose close to 100% of their excess weight.  

In general, though, we tell our patients they can expect to lose 70 to 75% excess weight loss with the Gastric Bypass, whereas the Gastric Sleeve has an average of 60 to 65% excess weight loss. 

Gastric Bypass vs. Gastric Sleeve Comparison

Duodenal Switch Expected Weight Loss 

When comparing bariatric procedures based on expected weight loss, the Duodenal Switch sees the best overall weight loss results. Patients who have a Duodenal Switch can expect to lose somewhere in the 80 to 90% range and will often lose up to 100% of their excess weight. 

So why not do this operation on everyone if it has the best weight loss results? Most of the time, this operation is too aggressive for patients who have a BMI in the 30s to 50s range and would likely find satisfactory results with the Gastric Bypass and the Gastric Sleeve. 

In general, we reserve the Duodenal Switch for patients whose BMI is well into the 50 and 60 range so they can maximize their weight loss. 

Timeline of Weight Loss

  • In the first 6 to 8 weeks after surgery, most patients (regardless of their procedure) will lose ~10% of their excess weight.
  • In the following 4 to 5 months, they can expect to lose a total of ~50% of their excess weight. 
  • Over the next 12 months, patients will generally lose an additional 50% of their excess weight, equally a total of 100%. 

After the first year of surgery, patients’ weight loss will typically begin to plateau.Generally speaking, patients can expect to hit their end weight, which is hopefully their goal weight, 18 months post-op.

Guide to Weight Loss

Other Factors Affecting Weight Loss

The expected weight loss ranges stated above are dependent on a variety of other social and environmental factors aside from the procedure you choose. 

The amount of expected weight loss will depend on the patient’s commitment to the process. Having weight loss surgery requires a commitment to making healthier food choices and increasing your overall activity level. 

how to lose weight after bariatric surgerySimilarly, expected weight loss can also be dependent on the patient’s environmental factors such as stress or lack of sleep as well as their genetics and gender. 

Due to the hormones that women produce, they will tend to lose about 10% less weight, and lose weight more slowly than men. Simiarly, age will be a determining factor in expected weight loss. Young patients have a higher metabolism and therefore are more likely to lose most weight after their bariatric procedure. 


For many patients who have tried and failed to lose weight on their own, or who feel as though their weight is out of control, weight loss surgery is the best solution for maximal and sustained weight loss. However, like any treatment, surgery is not fool-proof and results will vary based on each individual. 

The patients who see the best long term results are the ones who have a committment to teh process, change their eating habits, engage in regular physical activity, and develop habits to stay healthy. 

Don’t be fooled into thinking that surgery is a magic wand. Weight regain can occur when a person goes back to destructive eating behaviors that involve the consumption of excessive amounts of carbohydratesWith all this said, surgical weight loss will provide almost everyone with the BEST chance for an extreme amount of weight loss and weight loss maintenance.