Discussion of study in The Economist print edition Sep 29th 2005 Molecular self-loathing
Keep in mind that the stress response tends to lower immunity, and teenagers may be particularly vulnerable to stressful situations, partly due to hormonal and endocrine adjustments during maturation.
They are also likely to be exposed to a range of new microbes both in the varied classrooms of high school and when pursuing afternoon and evening activities unavailable to young children
Leading to the intriguing possibility that difficulties in navigating adolescence could result in some individuals sinking under the load of microbial influence and being branded by socio-professional ideas such as innate personality and temperament being a contributing factor, rather than an unfortunate outcome of immune overload.
An immune overload hypothesis would suggest that compensating withdrawal from some activities would help recovery from eating disorders, and certainly a reduction of unnecessary parental pressure may be needed.
Sample PubMed cite1)
Review provides new insights into the causes of anorexia New imaging technology provides insight into abnormalities in the brain circuitry of patients with anorexia nervosa (commonly known as anorexia) that may contribute to the puzzling symptoms found in people with the eating disorder.
I haven't researched this area in depth but this paper, which found an increase in methanogens in anorexics, appears to be the one people cite again and again. http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007125
I'm not sure I can completely tease out the significance of this study, but this sort of result suggests that famine may affect the microbiome in a lasting way: http://www.ncbi.nlm.nih.gov/pubmed/14696131
Final point: IMO, we should all be careful not to define the chain of events. What if a disruption in the microbiome preceded anorexia and the anorexia “phenotype” was only expressed in certain cultures?