It might be just as well that increased sugar intake is caused by mental disorders, as a form of self-medication. In my case for example, my sugar consumption fell drastically since I received ADHD medications. It turns out I was using sugar as a stimulant/calming agent for years, and no doctor properly figured it out.
You wanted a doctor to figure out you ate too many donuts and candy because of your ADHD?
That's pretty tough considering most people eat too much sugar just because.... it is good. Also it is easy as hell for EVERYONE to give up sugar once you are ADHD meds because they have a great appetite suppression effect.
That's not a special effect of mental disorders.