Despite its efficacy in studies, family-based treatment isn't for every family. For single-parent families, FBT can be "ruled out" as a treatment approach because of the time-intensive nature of treatment. Every meal, every snack, every day.
Of course, single-parent families can make it work. The other parent may be nearby and willing to help. Other caring adults can pitch in, or other family members. The parent may be able to take time off of work to care for their sick child until s/he is able to manage better on their own.
But the efficacy of FBT in single- vs. double-parent families hadn't been studied. In the International Journal of Eating Disorders, Daniel LeGrange and the team at the University of Chicago found that single-parent families were able to help their teens with bulimia nervosa as effectively as double-parent families.
Writes LeGrange in the introduction of the paper:
Given the emphasis in FBT on the involvement of the entire family in helping to reduce binge eating and purging behaviors, it could be that single-parent families demonstrate poorer outcomes than two-parent families receiving FBT. Although there is no research indicating that individuals from single-parent families have poorer outcomes in FBT for BN, there are several lines of indirect evidence to suggest that family status may relate to treatment outcomes.
First, single parent families may have less time, fewer social supports, or fewer financial resources than two-parent families. This could predispose single parents toward premature autonomy-granting or decrease their ability to provide adequate parental monitoring.
He also cites unconscious therapist bias against single parents being able to make FBT work, as well as evidence from AN treatment. Single-parent families battling AN benefit from 12 month FBT as opposed to the shorter-course 6 month treatment.
However, LeGrange et al. found:
There were no statistically significant differences between two-parent and single-parent groups on any of the treatment variables at post-treatment or 6-month follow-up...Patients in both groups showed significant reductions in eating disorder behavior and depressive symptoms as well as increases in self-esteem.
Part of the reason that FBT is just as effective in single-parent families is that in dual-parent families, responsibility isn't always shared equally between parents.
The study concluded:
Despite the reliance on parental intervention to reduce bulimic symptoms and normalize eating patterns, the results of this study suggest that FBT is an appropriate and efficacious treatment for single-parent families as well as two-parent families.