INFJ friend who i suspect has an eating disorder

i have an infj friend who i really care about and over the past years they've lost A LOT of weight. theyre over 6 feet and under 120 pounds. their legs are very very skinny. he used to be bigger( not fat but like an average build) a year and a half ago. Im really worried about him and so is almost everyone at my school, including the teachers but they are all too scared to tell him. I want him to be happy and healthy but i dont want him to take offense to me telling him this. how can i tell him that he needs to eat more and that he isnt taking care of himself? is there anyway i can say it in a way that makes him want to listen or actually go through with eating more?