Perceived Body Size in Relation to 10-Year Weight Change in the Swedish Obese Subjects Intervention Study.

Introduction: Body size underestimation in patients with obesity may be associated with long-term weight increase. In the current report, we analyse changes in body size perception in patients with obesity undergoing either bariatric surgery or usual obesity care, and in subgroups of patients who gain weight or maintain their body weight over 10 years.

Materials and methods: A total of 2,504 patients with obesity from the prospective, controlled Swedish Obese Subjects (SOS) intervention study were included in this report, 1,370 patients underwent bariatric surgery and 1,134 patients were usual care controls. Weight was measured and body size was self-estimated using the Stunkard's figure rating scale at baseline and after 0.5, 1, 2, 3, 4, 6, 8 and 10 years of follow-up. A body perception index (BPI) was calculated as estimated/measured BMI. Weight (re)gain was defined as ≥10% increase between 1 and 10 years of follow-up.

Results: Body size was underestimated by 12% in the surgery and 14% in the control group (i.e., >5 BMI units) at baseline and underestimation largely persisted over 10 years in both intervention groups. When stratified by long-term weight development, weight regainers from the surgery group underestimated their body size to a larger degree compared to weight maintainers (12 vs. 9%, p < 0.001) after 10 years. Likewise weight gainers in the control group also underestimated their body size to a larger degree (17% vs. 13%, p < 0.001). In both groups, the change in BPI was significantly different between weight regainers and maintainers during follow-up (time-BPI interactions both p < 0.001).

Conclusion: Patients with obesity underestimate their body size and this underestimation remains long-term even after major weight loss induced by bariatric surgery. In patients with obesity who maintain their weight, regardless of treatment, underestimation of body size persists but body size perception is slightly more accurate compared to patients who gain or regain weight long-term.