Dieters and weight loss researchers are familiar with the principle: The more weight you've lost, the harder it is to keep it off. A complex and vicious cycle of biological and behavioral factors make it so.
But eating disorder research has largely overlooked this influence, and Dr. Michael Lowe, a professor of psychology at Drexel University, has published a flurry of research studies showing that needs to change.
"The focus of eating disorder research has very much been on the state of patients' thoughts, beliefs, emotions and personalities," Lowe said. "And while these mental influences are undoubtedly part of the problem, historically there has been very little focus on how their current and past body weights contribute to their eating disorder."
Lowe and colleagues' studies - about a dozen on bulimia nervosa have been published in the past several years - show that having an elevated past body weight, and being at a body weight well below highest past weight, may help cause and perpetuate disordered eating. The latest of Lowe's studies was just published in The Journal of Abnormal Psychology, the top journal for eating disorder research, and is the team's first to address this principle in anorexia nervosa.
The findings, Lowe says, show that researchers and clinicians need to start taking into account how a person's historical and current body weight contribute to disordered eating.
"This fundamentally changes the assumption that the problem is primarily psychological or emotional," Lowe said.
The new study, led by doctoral student Laura A. Berner, was based on data collected at the Renfrew Center for eating disorders in Philadelphia, where Lowe is also a consultant. The researchers found that the level of eating disorder symptoms, as well as degree of improvement during treatment, depends on how much weight patients with anorexia nervosa had lost from their previous highest weight (a measure called "weight suppression"), how much they currently weigh and the interaction between the two.
After controlling for patients' body mass index (BMI, which is a known indicator of disease severity), they found that patients with greater weight suppression had more severe symptoms of anorexia than patients whose low weight was closer to their historical highest weight. Standard measures of disordered eating such as shape concerns, eating concerns, binge eating, depression and menstrual abnormalities were correlated with weight suppression, current BMI, or both.
Lowe said that researchers and clinicians who already use weight or BMI as an absolute measure of eating disorder severity should also consider weight suppression as a relative measure.
These findings also may have important implications for treatment.
"The standards for treating anorexia nervosa are all about 'how much weight do they need to gain to meet a minimally healthy body weight for their height,'" Lowe said. "What we've rarely asked, is 'what is this patient's weight history?'"
Lowe said his ongoing research suggests that the answer is that many patients weighed more than their peers before developing anorexia nervosa.
"If the patient's body somehow 'remembers' that past higher weight, then even at the minimally healthy body weight she is still going to be struggling mightily to maintain her weight," Lowe said. "That perspective is new. It suggests that future treatments might work toward finding a healthier 'balance point' between what patients once weighed and what they currently weigh."
"It is really helpful to have more than one way to look at weight in the eating disorders; we now have evidence that absolute weight and relative weight are both important in predicting difficulties in our work towards full recovery," said Dr. Susan Ice, vice president and chief medical officer of The Renfrew Center. "And it is immensely satisfying to find that science has discovered that there is physical memory or a kind of 'wisdom' in the body."