Gastric Bypass Patients Don't Lie About Their Post-Op Weight

Surgical Rounds®, December 2013,

Researchers from the University of Pittsburgh found that women and men who underwent gastric bypass surgery underreported their post-operative weight by an average of 1 kg or less.

While self-reported weights are easy to obtain, many researchers believe they are less accurate than those measured by a calibrated scale under medical supervision.

Previous studies have asserted that women tend to underreport their weight more than men. Those studies also indicated the degree of misreporting is related to body mass index (BMI), whereby overweight individuals tend to underreport and underweight individuals are inclined to overreport. However, a recent study published in JAMA found that among female gastric bypass candidates, self-reported pre-surgical weights averaged 0.3 kg more than measured weights, and misreporting was not significantly related to BMI.

In that study, Nicholas J. Christian, PhD, and colleagues at the University of Pittsburgh Graduate School of Public Health in Pittsburgh used data collected between April 2010 and November 2012 at annual assessments conducted 1 to 5 years after Roux-en-Y gastric bypass (RYGB) or laparoscopic adjustable gastric band (LAGB). The researchers mailed questionnaires to participants annually and asked them to disclose their weight from their last medical office or weight loss program visit, as well as their last self-reported weight taken at home. Of the 992 participants with weights meeting the inclusion criteria, only 4 were excluded due to suspected recording error. The remaining 988 participants included 164 patients with a self-reported medical weight, 580 with a self-reported personal weight, and 244 with both self-reported weights.

Across both types of self-reported weight, the researchers found that women and men underreported their weight by an average of 1 kg or less, and the degree of underreporting was not significantly different between women and men. Self-reported medical weights were significantly closer to measured weights than to self-reported personal weights for both sexes. In a general population survey, obese men and women underreported their weight on average by 1.32 kg and 2.99 kg, respectively.

As self-reported weights following bariatric surgery were close to measured weights, these findings suggest researchers could reasonably use self-reported weights when gathering data about surgically-induced weight change, and can be used when measured weights are not available.