Investigations of body mass, gastrointestinal, and dietary factors influencing the emergence and maintenance of eating disorders

Abstract

Eating disorders are severe psychiatric illnesses, characterized by dysregulated eating and distorted attitudes toward weight and body shape, causing enormous suffering for patients and their families. Although great progress has been made in eating disorders research during the past decades, many questions still remain regarding the etiology and consequences of eating disorders. The aim of this thesis was to extend the knowledge about the relationship among body mass index (BMI), gastrointestinal complaints, and diet, and how these factors contribute to the emergence and maintenance of eating disorders.

In Study I, we investigated the role of childhood BMI in later disordered eating behaviors across adolescence using a large, longitudinal twin cohort. BMI was reported at three time points (age 9/12, age 15, and age 18) and eating disorder symptoms were measured at two timepoints (age 15 and 18). We found a positive phenotypic correlation, meaning a correlation between BMI and eating disorders within the individual, that was stable across the ages. Further, we found a positive genetic correlation between the traits, indicating a common etiological pathway between BMI and disordered eating. In Study II, we explored the effect of childhood gastrointestinal problems on later eating disorder symptoms, in the same twin cohort as in Study I. We first estimated the association in the full cohort, finding those who reported having had gastrointestinal problems in childhood scoring higher on an eating disorder symptom scale. In a second step we conditioned the analysis on twin pairs who were discordantly exposed to gastrointestinal problems during childhood, meaning that only twin pairs where one twin was affected and the other one was not contributed to the analysis. We found a decreased positive, however not null, association between gastrointestinal problems reported at age 15 and disordered eating symptoms reported at the same age, which suggests that the relationship between gastrointestinal problems and disordered eating can in part be explained by shared familial confounding factors. In Study III, we evaluated the prevalence of functional gastrointestinal disorders (FGID) in different eating disorder diagnoses, as well as the association between specific eating disorder behaviors (binge eating, purging, laxative misuse, and fasting) and FGID, and lastly, we compared the total burden of FGID in individuals with high versus low current eating disorder symptoms, as well as controls. We found high prevalence of FGID in all eating disorders with up to half of the individuals with eating disorders reporting having three or more individual FGID. We found all eating disorder behaviors to be positively associated with most FGID categories. Lastly, we found those with lower current eating disorder symptoms to have lower total burden of FGID, although still higher than healthy controls, indicating a lingering effect of gastrointestinal problems. In Study IV, we aimed to explore the energy and nutrient intake in individuals with binge-type eating disorder (namely bulimia nervosa and binge-eating disorder) compared to healthy controls, and to the Nordic Nutrition Recommendations (NNR). We found women with bingetype eating disorders to have adequate intake of macronutrients (protein, fat, and carbohydrates), and most micronutrients (vitamins and minerals). However, women with binge-type eating disorders had a mean intake of energy per day that was significantly higher than controls, and higher than the recommended daily intake. In addition, women with bingetype eating disorders reported low adherence to folate, iron, vitamin D, and salt recommendations from the NNR. Although the number of men with binge-type eating disorders in the study was inadequate for statistical analysis, they did report a descriptively adequate dietary intake for most macro- and micronutrients.

The work presented in this thesis provides additional knowledge concerning the role that BMI and gastrointestinal problems play across childhood and adolescence in relation to the development of eating disorders. These insights, in combination with previous knowledge, can help develop new effective prevention strategies. This thesis also increases the understanding of the comorbidity between FGID and eating disorders, and clarifies the bidirectional relationship in the development of the two classes of disorders. Lastly, this thesis maps the energy and nutrient intake in individuals with binge-type eating disorders in relation to healthy controls, and to recommendations, and suggests a need for greater attention toward ensuring recommended daily intake of energy as well as of specific vitamins and minerals.