Researchers study how self-reported weights differ from measured weights after bariatric surgery

The JAMA Network JournalsNov 5 2013

In an analysis that included nearly 1,000 patients, self-reported weights following bariatric surgery were close to measured weights, suggesting that self-reported weights used in studies are accurate enough to be used when measured weights are not available, according to a Research Letter published online by JAMA.

"Obtaining standardized weights in long-term studies can be difficult. Self-reported weights are more easily obtained, but less accurate than those from a calibrated scale and may be inaccurately reported," according to background information in the article.

Nicholas J. Christian, Ph.D., of the University of Pittsburgh Graduate School of Public Health, and colleagues investigated whether self-reported weights following bariatric surgery differed from weights obtained by study personnel using a standard scale. They used data collected between April 2010 and November 2012 at annual assessments from the Longitudinal Assessment of Bariatric Surgery-2, an observational cohort study of 2,458 adults undergoing an initial Roux-en-Y gastric bypass (RYGB), laparoscopic adjustable gastric band (LAGB), or other bariatric procedure at 10 centers. Participants were sent mailed questionnaires each year and asked to report their: (1) weight from last medical office or weight loss program visit (self-reported medical weight) and (2) last self-weighing (self-reported personal weight).

The final analysis included 988 participants, including 164 with a self-reported medical weight, 580 with a self-reported personal weight, and 244 with both self-reported weights. Across the 2 groups who self-reported weight, women and men underreported their weight by an average 2.2 lbs. or less and the degree of underreporting was not different between women and men. Self-reported medical weights were closer to measured weights than were self-reported personal weights for both women and men.

"Small differences between self-reported and measured weights were found and may be due to differences in clothing, inaccurate personal scales, time between measurements, or intentional misrepresentation," the authors write. "Self-reported weights after bariatric surgery may be more accurate because participants who undergo surgery to lose weight may be especially attentive to their weight."