*2.1. Study Design and Population*

In the present cross-sectional study, a total of 581 participants along the impulsive– compulsive spectrum were included, as follows: *n* = 115 individuals with morbid obesity without diabetes (OB-DM), *n* = 67 individuals with morbid obesity and T2D (OB + DM), *n* = 107 individuals with anorexia nervosa restrictive subtype (AN-R), *n* = 121 individuals with gambling disorder (GD) and *n* = 171 healthy controls (HC). Participants in the AN-R and GD groups who presented with T2D were not included. Seven centers, all part of the Spanish Biomedical Research Centre in Physiopathology of Obesity and Nutrition (CIBERobn), participated in the study. The clinical groups were patients who had been consecutively referred to the clinics mentioned above. Healthy controls were recruited by means of word-of-mouth and advertisements at local universities, from the same catchment area as the clinical groups. The study was conducted according to the guidelines of the Declaration of Helsinki and its amendments, the International Conference on Harmonization Good Clinical Practice guidelines, and local regulatory requirements. The study was approved by the ethics committees of all participating institutions. Informed consent was obtained from all subjects participating in the study.
