Determining a healthy body weight for someone suffering from an eating disorder, especially if they are not yet done growing, seems as much art as it is science. (More information on how to determine ideal body weight can be found here) Yet the importance of setting a high-enough weight is rarely discussed, especially in an environment full of fears of childhood obesity.
It turns out that settling for a body weight even slightly below an individual's healthy set point can have long-term effects. A group of researchers at Schneider Children's Hospital examined the relationship between body weight, metabolism, and menstrual status in a group of normal weight adolescents with a history of AN, BN, and/or EDNOS. In a subset of these patients, resting energy expenditure was measured via indirect calorimetry.
The non-menstruating adolescents had an average of 98.5% ideal body weight, while adolescents with regular menses had 102.8% ideal body weight. Furthermore, the amenorrheic group had a significantly lower resting energy expenditure, indicating that their bodies were still operating as if their diets were restricted. In fact, this group also consumed a lower-fat diet than the menstruating group, which tacitly implies that these teens were still restricting their diets, even if their weight was within the "normal range."
In growing teens, even a short duration of amenorrhea can result in significant bone loss which can only be restored by full weight restoration and the resumption of menses.
Although the authors state that, "It is unclear whether participants with amenorrhea, despite achieving a BMI percentile of 47.6%, would require an additional, yet modest, amount of weight gain to resume menses," the dangers of not requesting that recovering ED patients gain a few more pounds seems to far outweigh any temporary discomfort of the adolescent.
"Perhaps metabolic recovery alone, where the focus would be to correct the caloric imbalance and increase dietary fat, would be sufficient. In addition, it would be helpful to determine the impact of a participant’s premorbid weight on influencing the chances for resumption of menses," the authors conclude.
(On a personal note, that ED specialists are trying to determine IBW without taking premorbid weight into account is quite disturbing, though not really all that surprising)
The weight differences between the two groups of adolescents was not that significant- approximately five pounds. Yet their nutritional statuses showed very different pictures. Although other factors certainly do play a role in the resumption of menses after an eating disorder, even slightly lower weights can make a huge difference both short- and long-term.