How do I talk to my daughter about her potentially disordered eating habits?

Posting from a throwaway, as my daughter uses Reddit regularly. I did consider posting this to r/relationships, but I'm not a very big fan of that sub at all.Background: my daughter (who I'll call 'T') is 21, and lives at home with her elder sister and myself. Their mother is very much out of the picture, and has been since their adolescence, due to her own mental health issues (primarily severe manic depression, garnished with a myriad of other issues) that render the girls unable to form any type of stable relationship with her. T is studying law, and although she rarely socializes, she does have a few good friends and a stable part-time job. Her sister has had depression since childhood, and I've always thought that I've done a fairly good job in making it obvious that mental illness is an open topic in our house, rather than something to be bottled up or ashamed of.A few days ago I had to dig through our garbage to try find an important document I knew I'd accidentally thrown away. As I was sorting through the garbage bags, I noticed one that was full of junk food packaging. Upon a closer look, there were several takeaway food containers, an ice cream tub, doughnut boxes, biscuit packages. It was a lot. At first I thought maybe one of our neighbours had used our bin if theirs was full, but there were also several banking letters with T's name on them in the same bag.I was initially extremely surprised and shocked, because T has been a very healthy eater since she was around 18, and has never shown any sort of problematic food-related behavior before. To my knowledge, she doesn't touch any of the stuff. Everyone in our family knows her to be the most health-conscious. Upon doing a lot of thinking, though, I think I may have missed some signs. In addition to rarely socializing, she never eats out with anyone, ever, and she has definitely gained weight over the past couple of years despite being an outwardly healthy eater (I always attributed this to the fact that young women inevitably seem to gain some weight at her age).I have no idea how long this has potentially been an issue for, and I'm obviously incredibly worried. I'm unsure as to how I should talk to her about this, as I know she will a) deny it was hers, or b) shut down and refuse to talk to me. I really don't want to accidentally push her away or trigger anything further.Thank you in advance to anyone with any advice. via /r/Parenting http://ift.tt/2dxuVSt