PREreview of Weight suppression, bingeing, and purging as predictors of weight gain during inpatient treatment in persons with bulimia nervosa

This study examined predictors of weight gain during inpatient treatment for bulimia nervosa. Higher weight suppression predicted greater weight gain, particularly in those with lower BMI at admission. Unlike previous research, this study also explored the role of bingeing and purging in weight changes. Findings showed that more frequent purging and less severe bingeing were linked to greater weight gain, while more frequent bingeing combined with infrequent purging reduced this effect.

Major strengths

• Open access data and code- Transparency was improved by the publication of code and data on the OSF, supporting reproducibility and future research.

• Easy to follow- This paper was well-structured and clearly presented, making it an easy read. 

• Novelty- Inclusion of bingeing and purging as a predictor of weight change adds a unique perspective, going beyond traditional factors like weight suppression and BMI.

Major issue

• Limited Practical Impact- Overall weight gain during treatment for bulimia nervosa is typically minimal, raising concerns about the study’s practical significance. The authors should clarify how predicting small weight changes contributes to treatment planning- Is there evidence that predicting weight gain could enhance adherence? A stronger discussion of how weight gain may impact treatment adherence and how clinicians could use these predictors in therapy would improve the study’s contribution.

Minor issues

• Stronger Literature Grounding- The introduction lacks citations of key relevant studies, including:

  • ‘Impact of pre-treatment weight on weight trajectory in women treated for bulimia nervosa’ (Carter et al., 2004)

  • ‘Patterns of weight change after treatment for bulimia nervosa’ (Carter et al., 2004)

  • ‘The independent and interacting effects of weight suppression and admission body mass index on treatment weight change in patients with anorexia nervosa or bulimia nervosa’ (Piers et al., 2019).

• Duration of Treatment- The average length of inpatient stay is not reported, making it unclear how much of the typical treatment duration the study captures. Relatedly, consider removing claims that this study measures ‘from admission to discharge’.

• Placement of Linearity Testing Results – The results of testing the linearity of weight change should be moved from the Analysis section to the Results section, as they are discussed as a finding in the Discussion and Abstract.

• Significance Threshold – The use of a stricter significance level (p < .005) to reduce false positives is commendable. However, confirmation that this decision was made a priori (e.g., through pre-registration) would have strengthened the study’s methodological transparency. We note that this cannot be rectified now.

• More Meaningful Interpretation of Results – The study could present findings in more clinically relevant terms, such as: “One extra weekly purge is associated with X increase in BMI over 10 weeks.” This would enhance the practical understanding of the results.

• Narrow Discussion- While the authors commendably avoid overextending clinical implications from limited data, the discussion could provide a deeper analysis of the study’s relevance. Instead of primarily calling for further research, the authors could explore potential clinical applications based on their findings.

Competing interests

The authors declare that they have no competing interests.