Bariatric Journal

Gastric Bypass Expected Weight Loss, Results after Surgery

Gastric Bypass Expected Weight Loss & Results

Gastric bypass surgery is a weight loss procedure that combines both restrictive and malabsorptive mechanisms to bring about a significant weight loss with additional benefit of improvement or even total resolution in obesity-associated disease conditions such as type 2 diabetes mellitus, hypertension, osteoarthritis, dyslipidemia, sleep apnea, etc.

The surgery entails the creation of a small compartment (pouch) from the upper part of the stomach while the rest of the stomach is bypassed. The pouch is then connected to the small intestine with refashioning that exclude a considerable length of the small intestine from digestion and absorption. The newly created stomach pouch has a small capacity and can only accommodate small amount of food, therefore, limiting the calorie intake. In addition reduced absorption takes place only from the functional segment of the intestine.

Weight loss outcome is measured by calculating the percentage of the excess weight that a patient has lost at a particular time after the surgery. This parameter differs from one person to another at a particular time after surgery. Studies have shown that many factors are responsible for different degrees of weight loss after bariatric surgery. The age of the patient at the time of surgery, the gender, and race, level of physical activities and emotional status of the patient are some of the factors.1The competency of the surgeon also has effect on the degree of weight loss.

Excess weight loss (%age) = excess weight prior to surgery – excess weight post-surgery ₓ 100

Excess weight prior surgery

Overall, weight loss after gastric bypass surgery averages 70% at 12-18months after surgery. In a review of about 136 different studies by Buchwald et al., more than twenty-two thousand patients had weight loss surgeries with those who had gastric bypass recording an average percentage excess weight loss of 68%.2Similar review by Trastulli et al. revealed an percentage of excess weight loss ranging from 62% to 94% in patients who had gastric bypass surgery.3

Apart from weight loss, gastric bypass surgery like other weight loss surgery has been shown to lead to resolution/improvement in comorbid conditions. Mingrone and his co-workers reported a remission of type 2 diabetes mellitus in 75% of patients who had gastric bypass surgery.4

The summary of improvement in disease conditions associated with obesity implies that after gastric bypass surgery

  • Your need for antihypertensive drugs will reduce either by the number of drugs or by dosage.
  • Your blood sugar will improve and the need for anti-diabetic drugs will reduce
  • Those on CPAP machine due to obstructive sleep apnea will begin to experience a quality sleep without the machine.
  • Improvement in the symptoms of heartburn
  • The risk of stroke or myocardial infarction will be significantly lowered due to improvement in blood cholesterol profile.
  • Overall increase in the quality of life and lifespan.

Gastric bypass is not without some negative consequences. These are the unwanted side effects that often discourage obese patients from going for the surgery but the good news is that they are not insurmountable. The side effects of gastric bypass surgery include dumping syndrome, dehydration, nutritional deficiencies, gallstone, hair loss, redundant skin, etc.

In conclusion, gastric bypass result after surgery is mostly positive with a satisfactory weight loss, reversal of comorbid conditions, improvement in the quality of life, minimal side effects and increase in lifespan.


  • Pories WJ. Bariatric Surgery: Risks and Rewards. The Journal of Clinical Endocrinology and Metabolism. 2008;93(11 Suppl 1):S89-S96. doi:10.1210/jc.2008-1641.
  • Buchwald H, Avidor Y, Braunwald E et al. Bariatric Surgery: a systematic review and meta-analysis JAMA. 2004;292(14):1724. doi:10.1001/jama.292.14.1724.
  • Trastulli S, Desiderio J, Guarino S et al. Laparoscopic sleeve gastrectomy compared with other bariatric surgical procedures: a systematic review of randomized trials. Surgery for Obesity and Related Diseases. 2013;9(5):816-829. doi:10.1016/j.soard.2013.05.007.
  • Mingrone G, Panunzi S, de Gaetano A, et al. Bariatric surgery versus conventional medical therapy for type 2 diabetes. The New England Journal of Medicine. 2012;366(17):1577–1585

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