Further psychometric validation of the BODY-Q: ability to detect change following bariatric surgery weight gain and loss

Evidenced-based patient-reported outcome (PRO) data is needed for bariatric surgery [1‐4]. PRO instruments measure outcomes that matter to patients (e.g., symptoms, health-related quality of life (HR-QOL)), by asking them directly [5]. Such instruments are being used worldwide to inform patient care, as quality metrics, in audit studies and in comparative effectiveness research [6‐9]. Some countries (e.g., United Kingdom, Netherlands, Sweden) use PRO instruments at a national level to compare providers or in clinical registries [8, 9].

Outcome measures should be fit for purpose, i.e., capture the concepts of interest (e.g., physical function) in the context of use (e.g., patients attending a bariatric surgery clinic) [5]. A number of recent systematic reviews have pointed out limitations in the content of current PRO instruments measuring HR-QOL in bariatric surgery research [2‐4]. For example, the most common PRO instrument used in bariatric research is the generic Short Form-36 (SF-36) http://​www.​qualitymetric.​com. This instrument has been critiqued for failing to measure a range of concepts important to patients undergoing weight loss (e.g., sexual function, self-esteem, appearance) [10]. The most common obesity-specific tools used in bariatric research include the Impact of Weight on Quality of Life-Lite (IWQOL-Lite) [11, 12], and Moorehead-Ardelt Quality of Life Questionnaire (MAQOL) [13]. These instruments measure a range of obesity-specific concepts. The IWQOL-Lite, for example, measures physical function, self-esteem, sexual life, public distress and work [12], while the MAQOL has a total of 6 items covering self-esteem, physical, social, work, sexual and eating behavior [13]. A limitation of these obesity-specific instruments is that their measurement model (classical test theory; CTT) lacks evidence that the summed scores provide meaningful measurement [14, 15]. For example, in the CTT approach, it is considered legitimate to provide a total score for a PRO instrument that adds up scores for scales (IWQOL-Lite) or items (MAQOL). This approach to measurement is not helpful in clinical trials as it can mask effects of treatment [14, 15], for example when patients who undergo weight loss improve on some scales or items (e.g., physical function as they lose weight) and not others (e.g., body image because of the development of excess hanging skin).

The BODY-Q [16] represents a new generation PRO instrument that was developed using a modern psychometric approach called Rasch Measurement Theory (RMT) [17]. In RMT, scales that compose a PRO instrument are each designed to measure and score a unidimensional construct (no total score). In scale development, data that meet the requirement of the Rasch model provide interval-level measurement [15]. When a scale has high content validity and is targeted to measure a concept as experienced by a sample, accurate tracking of clinical change can be achieved [15].

The aim of the present study was to measure clinical change for 13 BODY-Q scales/checklist that measure appearance (of upper arms, abdomen, back, body, buttocks, inner thighs and hips/outer thighs) and HR-QOL (body image, obesity-specific symptoms and psychological, social, sexual and physical health) following bariatric surgery for participants from the BODY-Q field-test study who were recruited from the St Joseph’s Healthcare Hamilton bariatric program in Canada.

The survey was completed by 58 (response rate 65%) of the 89 participants who were sent an invitation to complete the follow-up survey. The 58 participants did not differ from the 49 participants non-participants who provided data at baseline in terms of age, gender, ethnicity, BMI, or any of the BODY-Q scores completed by the sample at time 1.

Of the 58 participants, 4 had not undergone bariatric surgery at follow-up and were excluded from the subsequent analyses. Of the 54 remaining participants, age ranged from 27 to 71 years (mean = 48, SD = 12), 42 (77.8%) were female, and 44 (81.5%) were Caucasian. The mean time since bariatric surgery was 2 years (SD = 0.5; from 0.4 to 3 years). Baseline BMI was 50 (SD = 7), and at follow-up was 35 (SD = 7). All participants lost weight: mean %TWL was 31 (SD = 9; from 12 to 51). Dissatisfaction with weight was reported by 51 (95%) participants before bariatric surgery and 20 (37%) participants at follow-up. Body contouring to remove excess skin had been obtained by 3 (6%) participants, while 40 (74%) participants indicated that they needed body contouring to remove excess skin from one or more areas of their body.

The BODY-Q represents a new generation PRO instrument developed and validated using a modern psychometric approach to provide a set of unidimensional, scientifically sound scales that measure concepts of interest important to patients undergoing weight loss and/or body contouring. Our findings show that BODY-Q scales were responsive to measuring clinical change in patients who underwent bariatric surgery. The variation in effect sizes and standardized response means, from no change to moderate and large change across scales illustrates why it is important to provide separate results for each scale rather than sum to produce a total score for scales measuring different concepts.

Bariatric surgery is often pursued by people aiming to improve their physical and psychosocial HR-QOL. However, massive weight loss often leads to excessive skin, which can have a negative influence on HR-QOL [24]. The BODY-Q was specifically designed to measure outcomes important to patients over the entire patient journey starting at obesity and ending after body contouring to remove excess skin. We found that participants improved in terms of body image, social and physical function, and reported fewer obesity-specific symptoms. Our sample did not improve in terms of psychological and sexual function. These findings are in line with recent systematic reviews of intermediate and long term HR-QOL in bariatric surgery. Jumbe et al. [3] examined 11 studies focused on the long-term effectiveness of bariatric surgery on quality of life compared to non-surgical interventions. These researchers found that long-term psychosocial quality of life did not appear to improve following bariatric surgery despite significant improvements in physical quality of life over time. Similarly, Kubik et al. [25] evaluated the impact of bariatric surgery on psychological functioning based on 27 articles and concluded that bariatric surgery results in mental health gains in the short-term, but this effect was not sustained beyond two years’ post-surgery. Hachem and Brennan [4] compared bariatric surgery with alternative weight-loss interventions and between different bariatric surgical procedures based on 15 controlled trials and showed that physical function consistently improved following bariatric surgery, but that improvements in mental health and psychosocial function were mixed. Raaijmakers et al. [2] examined short and long-term effects of bariatric surgery compared with community norms based on 36 studies and found that while quality of life significantly improved after surgery, a few studies showed no significant improvement in the mental health component of quality of life. Authors from these reviews pointed out limitations in current literature (e.g., lack of consensus on the choice of PRO instruments used) and called for more research to gain a greater understanding of the effects of bariatric surgery on the health of patients.

Though our sample is small, the authors of a large cross-sectional study of 493 bariatric surgery patients from Denmark compared BODY-Q scores for 4 phases of the weight loss journey: pre-bariatric surgery, post-bariatric surgery (4/5 or 12 months post-surgery), pre-body contouring surgery, and post-body contouring surgery [26]. BODY-Q scores for appearance and HR-QOL were lowest in the pre-bariatric phase, followed by patients in the pre-body contouring phase. The Danish findings suggest that outcomes following bariatric surgery are not optimal until body-contouring to remove excess hanging skin is performed, and they call for longitudinal research to measure the full extent of HR-QOL and appearance change following weight loss and reconstructive treatments. In the present study, the majority of participants reported that they needed body contouring surgery to remove excess skin in order to complete their weight loss journey, which could account for the lack of improvement in psychological and sexual function.

This study has some limitations. The response rate was low and our sample size was small. Although we did not find any differences between the group of non-respondents and respondents on demographic, clinical and BODY-Q scores, there could still be bias in the sample of patients who completed our survey. Another limitation is that the participants were from a single bariatric surgery centre in Canada and may not represent the bariatric patients in other centres or other countries. Finally, the clinical data collected were self-report and could have errors due to participants guessing (e.g., date of bariatric surgery).

Participants in our sample were at various stages in their weight loss journey, with many requiring body contouring to remove excess skin after massive weight loss. While it is clear that bariatric surgery leads to improvement in physical health, evidence-based information is still needed to show the full extent of psychosocial, sexual and body image/appearance change that follows weight loss across the entire journey.