Bariatric surgery is a metabolic surgery which targets the root cause of obesity i.e. caloric excess. It is an internal surgery which doesn’t remove the superficial fat but rather reduces the size of stomach and the small intestine. This in turn leads to decreased intake and absorption of food which causes a long-term caloric deficit leading to weight loss.
The weight loss after bariatric surgery occurs gradually over a period of 12-15 months. There is an initial period of relatively rapid weight loss lasting for 3-4 months followed by a more gradual weight loss which occurs over the next 8-10 months. The patient is expected to lose between 60-90% of the excess body weight in this time frame depending upon the type of procedure and lifestyle compliances’ followed after the surgery.
Most of the weight loss is due to burning of the stored fat which is consumed to compensate for the caloric deficit induced by the effect of surgery. There is also the effect of certain gut hormones which boost the metabolic rate and increase the energy expenditure after the operation. The overall effect is a gradual and sustained weight loss which can be maintained over the long term. After the weight stabilises, there is a new energy balance established in the body in which the caloric intake matches the new requirement according to the reduced body weight.