The relation of weight suppression and BMI to bulimic symptoms.

Weight suppression, which is the discrepancy between a patient’s highest weight and current weight, may be an important factor in the course and outcome of bulimia nervosa (BN). Individuals who are weight suppressed weigh less than they once did. Because patients with BN usually present for treatment at a normal weight, the fact that many were once overweight or obese is often overlooked (1). The average weight suppression for BN patients is high, with those in outpatient or residential treatment having average levels of 9.6 kg and 12.0 kg, respectively (2,3). Healthy college students, by comparison, have a mean weight suppression of 2.7 kg (4). The perpetual dieting and/or compensatory behaviors that are needed to maintain a suppressed weight could maintain binge eating and purging. This large reduction in weight also could make patients with BN more susceptible to weight gain (possibly due to reduced metabolic rate, increased overeating, or both), leading to even greater dietary restriction, which maintains the binge/purge cycle (2, 5). Two studies have found that weight suppression predicted weight gain in patients with BN (β = .21, p = .03, 4.7% of variability in weight gain (3); B = 0.100, SE = 0.04, p =.01, Exp (B) = 1.11, R2= 0.06 (6)). This weight gain could cause increased body image dissatisfaction and lead to higher rates of disordered eating in an effort to avoid future weight gain or to lose the undesired weight. Additionally, since many individuals with BN were previously overweight, they may have an even greater fear of weight gain because they have previously seen those fears realized. This fear of weight gain could also contribute to greater levels of dieting and compensatory behaviors. Research has shown that patients who are high in weight suppression, compared to their peers with lower weight suppression, have a higher frequency of objective binge eating ((β = .319, p< .05), a higher probability of maintaining a bulimic syndrome over 10 years (7), a higher risk of dropping out of treatment (B = −0.37, SE = 0.07, p =.01, Exp(B) = 0.69) (2), and a lower chance of abstaining from binge eating and purging by treatment completion (2, 6, 8). Weight suppression is calculated by two factors: current weight and highest weight. Research has examined whether either factor is predictive above and beyond weight suppression. To date, highest weight has not been predictive of BN symptoms or treatment outcome (2, 8). However, current weight is independently predictive of BN symptoms and outcome, with those who have lower weights demonstrating higher rates of BN pathology (9) and higher risk of treatment dropout (10). Despite research suggesting that both current relative weight and weight suppression are predictive of bulimic pathology, no study has investigated the potential interaction between current weight and weight suppression. Individuals who have high weight suppression and low current weight might have the greatest motivation to stay thin, and may engage most in unhealthy eating behaviors. Individuals who are high in weight suppression and have a relatively high weight or those who are thin but not weight suppressed may have less severe symptoms, possibly because these individuals are not as afraid of weight gain or experience less biological pressures toward weight gain. In addition, the combination of high weight suppression and low weight could engage defensive biological mechanisms that could induce more binge eating and metabolic efficiency and therefore predispose these individuals towards weight gain. To test this hypothesis, the current study examined weight suppression, body mass index (BMI), and the interaction between weight suppression and BMI as predictors of bulimic symptoms upon admission to treatment. It was hypothesized that weight suppression and BMI would be independent predictors of bulimic symptoms, and that the interaction would be significant, with patients who have high weight suppression and low BMI demonstrating the most bulimic symptoms.