I’ve been addicted to food, drugs, alcohol, and sex since I was 15 years old. To this day, the only thing I still struggle with is food-- in part due to its essential aspect to our existence.
Regardless-- eating disorders are very real and have been scientifically researched thoroughly. I am a binge eater-- I will go the whole day eating perfect-- completely on spot with my calorie intake, with regards to protein/carbs/fats the whole T-Nation deal, but nearing night time I still have to struggle to control this insatiable appetite that seemingly consumes me.
One night I ate 2 full pizzas, 6 carnitas tacos, a PB&J along with a bag of blue tortilla chips. Of course I felt terrible, both physically and mentally. The only thing you can do is to remind yourself there is another day tomorrow, and to have the mentality that that day is the first day of the rest of your life.
It may sound corny, it may sound feminine, but you have to kind to yourself and realize we all make mistakes and struggle with different aspects of our lives-- but you must also try your hardest to improve your life while striving to achieve what you believe you never could.
Basically, I would present your friend with an open and understanding demeanor while trying to bring him or her along with you when you do healthy activies, such as baseball/basketball/walks/runs whatever it may be.
Maybe sometime go grocery shopping with him or her and point out some good super healthy foods that are easy to do, some “did you know” foods that arent as unhealthy as some would think.
Ultimately it is his or her decision to make the lifestyle change and it is him or her that is struggling with the demon day in day out, but if you are truly concerned, you can take a few small steps to help cattle prod his or her progress.
Of course, never let these type of problems of others effect your life, but a little helping hand goes a long way.