Early within‐person weight gain and variability during inpatient treatment for anorexia nervosa: Age‐dependent effects on treatment outcome

Abstract

Objective Early weight gain during inpatient treatment for anorexia nervosa (AN) is a dynamic process characterised by within‐person variability that may be age‐dependent. We examined whether age moderates the effect of within‐person weight gain and variability on treatment outcome. Method Within‐person level estimates of N = 2881 underweight adolescents and adults with AN for daily average weight gain (linear slope) and variability (root mean squared errors) were obtained using random‐effects modelling. Between‐person level regression analyses were calculated to assess effects on weight, eating disorder psychopathology and attaining normal body weight (body mass index [BMI]: 18.5–25 kg/m2). Results Higher weight gain during first 2 weeks of inpatient treatment predicted higher weight, lower drive for thinness and lower body dissatisfaction at discharge, but not lower bulimic symptoms. Moreover, it predicted a higher probability of discharge weight within normal range. Younger age was associated with stronger effects of early weight gain on weight, drive for thinness and body dissatisfaction at discharge. Weight variability was not associated with any outcome. Conclusions Age moderated effects of early weight gain on treatment outcomes, with larger effects for younger patients. Weight variability alone did not influence treatment across age and should be of lesser clinical concern during early inpatient treatment.

Exploring Gender Differences in Early Weight Change and Variability in Adolescents with Anorexia Nervosa during Inpatient Treatment

“…It is important to note that the effects of weight fluctuations, as measured by the degree of variation around a patient’s weight regression line, have thus far only been investigated for AN in two studies, with varying results. Whereas Kolar et al [ 10 ] found no effects of weight variability on treatment outcomes in adolescent and adult patients, higher weight variability predicted poorer weight gain in adults in Hartmann et al [ 11 ]. Besides the difference in sample choice, neither study analyzed effects of weight variability stratified by gender; this might be a further explanation for the reported discrepancies between studies and highlights the need for further investigations.…”

“…BMI-SDS shows the deviation of a patient’s BMI from the population mean and allows for age- and gender-adjusted body weight comparisons. Similar to previous studies [ 10 , 36 ], we then computed daily weight change and weight variability within the first two weeks of treatment (starting with day 0 at admission and ending on day 13), using the slopes and root-mean-squared errors (RMSE) of residuals from a linear mixed model. The model used changes (increase or decrease) from baseline BMI-SDS to current BMI-SDS as dependent variable, and included an intercept and a fixed effect of day of treatments, with by-patient random variation of slope and intercept.…”

“…The model used changes (increase or decrease) from baseline BMI-SDS to current BMI-SDS as dependent variable, and included an intercept and a fixed effect of day of treatments, with by-patient random variation of slope and intercept. The slopes of this model estimate, for each patient, the linear increase or decrease from admission BMI-SDS with each day of treatment (i.e., the Daily Weight Change) [ 10 ], and the RSME estimates the degree of variation of a patient’s weight around this regression line.…”

“…Early treatment responses, especially weight gain during the first weeks, have been linked to improved AN treatment outcomes [ 6 ]. Early weight gain and fewer weight fluctuations have been linked to normalized discharge weight and improved psychopathology [ 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. However, recent findings suggest that adolescents’ early weight changes might differ by patient gender [ 14 ], raising the question of whether evaluating young men’s and women’s clinical data during AN treatment may require different criteria.…”

“…Specifically, we were interested in (a) whether young men and young women with AN differ in terms of admission psychopathology and early treatment response and, most importantly, (b) whether early treatment responses predict AN treatment outcomes similarly across genders. Based on the available data, early treatment responses were defined in terms of weight changes and weight variability (i.e., weight fluctuations around the trajectory of weight change) during the initial 14 days of treatment, which have specifically been linked to treatment outcomes among adolescents with AN [ 10 ].…”