A correlation method for weight loss after gastroplasty

Prevalence of morbid obesity is increasing in western countries. As a consequence, bariatric surgery has intensively developed in the last decades. Someone facing the need for comparison between gastric restrictive procedures could find it useful to have a general expression for weight loss after surgery.

A first approach of this issue can be made, taking into account two simple hypotheses: linear dependencies of weight variation versus sum of energy transfer, and of loss of energy versus weight. With the additional assumption of a constant energy income (the goal of surgery), one can obtain for the weight loss DeltaP=P(0)-P=(P(0)-B)(1-e(-betat)), where P and P(0) are the weight at time t and t(0), B and beta being adjustable constants.

A preliminary study has shown us that most of our weight loss data could be fitted using such an expression. The model was successfully tested on gastric banding and calibrated vertical banded gastroplasty data, but with greater emphasis on laparoscopic vertical banded gastroplasty.

We introduce a simple, exponential growth-like function that can be used for the fit of weight loss data of patients who underwent bariatric surgery in our surgical unit. Such a function could also be of practical interest for the survey of weight loss.