i've had at least one moderate to severe anxiety disorder for my entire life and have always been very skinny (and at times unhealthily skinny) even though i've always had a strong appetite and an aversion to physical activity. when i started taking anti-anxiety meds earlier this year i gained about 30 pounds in a few months despite eating about the same and working out on a daily basis for the first time in a decade or so. at some point the side effects of those meds became too much to deal with so i stopped taking them. my anxiety returned, i stopped working out, didn't change my diet (started eating worse in fact), and still lost those 30 pounds in about 5 months

fair warning: depending on what kind of anxiety you have, it's likely going to get much worse once you hit 30. mine was always pretty manageable in my 20s but ~6 years ago, around the time i turned 30, it became completely unbearable. it turns out that 31 is the average age that generalized anxiety disorder sets in. if you can start taking steps now to learn how reduce your anxiety on a physiological level (meaning regular exercise, a better diet, learning how to reset your autonomic nervous system at will, etc.), you'll be in a better position to deal with it, should it happen