Worth noting that the vast majority of the participants in this study had existing mental disorders, 57% "generalized anxiety", 51% ADHD, 17% Major Depression,

Worth noting that the vast majority of the participants in this study had existing mental disorders, 57% "generalized anxiety", 51% ADHD, 17% Major Depression, 7.4% Bipolar Disorder, and so on. The authors claim (but don't show their work) that adjusting for these factors did not change the statistical significance of the relationship, but it does still mean this isn't exactly a representative sample of the population. Very interesting that underweight people generally have more blood flow than "normal" weight people, though if you dive into the supplementary data that doesn't hold for every region of the brain studied (and the general trend seems to hold in all regions studied).