Body mass index was calculated as weight in kilograms divided by height in meters squared. The dashed blue line indicates the mean weight difference. About 95% of the points are expected to fall within 2 SDs of the mean, indicated by the blue shaded areas. For women, self-reported medical weight, the mean ± 2 SD is −3.7 to 3.5 and is −4.6 to 2.8 for self-reported personal weight. For men, self-reported medical weight, the mean ± 2 SD is −5.6 to 5.8 and is −6.4 to 3.4 for self-reported personal weight.
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Christian NJ, King WC, Yanovski SZ, Courcoulas AP, Belle SH. Validity of Self-reported Weights Following Bariatric Surgery. JAMA. 2013;310(22):2454–2456. doi:10.1001/jama.2013.281043
Obtaining standardized weights in long-term studies can be difficult. Self-reported weights are more easily obtained but are less accurate than those from a calibrated scale and may be inaccurately reported. Previous studies have reported that women tend to underreport their weight more than men with the degree of misreporting related to body mass index (BMI), whereby overweight individuals tend to underreport and underweight individuals tend to overreport.1-4 However, in a study of female gastric bypass candidates, self-reported presurgical weights averaged 0.3 kg more than measured weights and misreporting was not significantly related to BMI.5
This study investigated whether self-reported weights following bariatric surgery differed from weights obtained by study personnel using a standard scale.
The Longitudinal Assessment of Bariatric Surgery-2 is an observational cohort study of 2458 adults undergoing an initial Roux-en-Y gastric bypass (RYGB), laparoscopic adjustable gastric band (LAGB), or other bariatric procedure at 10 centers.6 This report uses data collected between April 2010 and November 2012 at annual assessments conducted 1 to 5 years after RYGB or LAGB. Each center had institutional review board approval and all participants provided written informed consent.
Annually, participants were asked to report on mailed questionnaires 2 postoperative weights and the dates that those weights were measured: (1) weight from last medical office or weight loss program visit (self-reported medical weight) and (2) last self-weight (self-reported personal weight). Self-reported weights could be from any scale with or without shoes or bulky clothing.
Using standardized data collection protocols, study personnel measured height before surgery using a stadiometer and measured weights before surgery and annually afterward on a standard scale (Tanita Body Composition Analyzer model TBF-310, Tanita Corporation of America Inc) without shoes and bulky clothing (measured weight).
Participants with postoperative measured weights and self-reported weights from no more than 30 days before the measured weight were included. If both self-reported weights met this criterion then both were included. If participants had self-reported and measured weights meeting this criterion at multiple time points, weights from 1 randomly selected time point were used. Selected participants are a convenience sample of the total cohort who met the inclusion criterion.
Statistical significance of weight differences was assessed using t tests for each type of self-reported weight and normal mixed models for all self-reported weights combined. Analyses were conducted using SAS statistical software version 9.2 (SAS Institute Inc). Two-sided P values of less than .05 were considered statistically significant.
Of the 992 participants with weights meeting the inclusion criteria, 4 were excluded because of suspected recording error. The 988 participants included 164 with a self-reported medical weight, 580 with a self-reported personal weight, and 244 with both self-reported weights. The characteristics of the included participants appear in the Table.
Across the 2 types of self-reported weight, women and men underreported their weight by an average of 1 kg or less (range, underreported by 10.9 kg to overreported by 11.8 kg) and the degree of underreporting was not significantly different between women and men (Table). Self-reported medical weights were significantly closer to measured weights than were self-reported personal weights for both women and men. Weight differences did not vary systematically by measured BMI or percentage of weight change from baseline (Figure).
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. In a general population survey, obese men and women underreported their weight, on average, by 1.32 kg and 2.99 kg, respectively.3 We found smaller differences. 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.
A limitation of this study is that it used a convenience sample of participants whose self-reported weights were no more than 30 days before a measured weight. Those participants who anticipated being weighed by study personnel may have been more likely to report accurately.
In conclusion, self-reported weights following bariatric surgery were close to measured weights. This suggests that self-reported weights may not unduly affect study results of surgically induced weight change and can be used when measured weights are not available.
Corresponding Author: Nicholas J. Christian, PhD, University of Pittsburgh Graduate School of Public Health, 130 DeSoto St, 127 Parran Hall, Pittsburgh, PA 15261 (firstname.lastname@example.org).
Published Online: November 4, 2013. doi:10.1001/jama.2013.281043.
Author Contributions: Dr Christian had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Christian, Belle.
Acquisition of data: Courcoulas.
Analysis and interpretation of data: Christian, King, Yanovski, Courcoulas, Belle.
Drafting of the manuscript: Christian.
Critical revision of the manuscript for important intellectual content: Christian, King, Yanovski, Courcoulas, Belle.
Statistical analysis: Christian, Belle.
Obtained funding: Belle.
Administrative, technical, or material support: Courcoulas, Belle.
Study supervision: Belle.
Conflict of Interest Disclosures: The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Courcoulas reported receiving research grants from Allergan, Pfizer, Covidien, EndoGastric Solutions, and Nutrisystem; serving on a scientific advisory board of Ethicon J & J Healthcare system; and serving as a consultant to Ethicon J & J Healthcare system. No other disclosures were reported.
Funding/Support: Longitudinal Assessment of Bariatric Surgery-2 was a cooperative agreement funded by the following grants from the National Institute of Diabetes and Digestive and Kidney Diseases: U01 DK066557 (awarded to the data coordinating center), U01-DK66667 (Columbia University Medical Center; in collaboration with Cornell University Medical Center grant UL1-RR024996), U01-DK66568 (University of Washington; in collaboration with grant M01RR-00037), U01-DK66471 (Neuropsychiatric Research Institute), U01-DK66526 (East Carolina University), U01-DK66585 (University of Pittsburgh Medical Center; in collaboration with grant UL1-RR024153), and U01-DK66555 (Oregon Health & Science University).
Role of the Sponsor: Scientists from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) contributed to the design and conduct of the study. The project scientist from the NIDDK served as a member of the steering committee, along with the principal investigator from each clinical site and the data coordinating center. The decision to publish was made by the Longitudinal Assessment of Bariatric Surgery steering committee, with no restrictions imposed by the sponsor. As a coauthor, an NIDDK scientist contributed to the interpretation of the data and preparation, review, and approval of the manuscript.