Shaming isn't the way to go, the best way to help someone with weight problems is to encourage them to get healthier in a positive way. Help them exercise and go on a diet with them. Positive encouragement is always the best. Back when I was in high school I was 50lbs overweight, yes I felt like shit knowing it was unhealthy but I wouldn't push myself into getting better until one of my ROTC instructors that served in the marines encouraged me that I can get into great shape if I eat right and work out on a weekly basis, surely I was skeptical and didn't want to go through with it but he insisted on helping me getting back to my proper size. We worked out after school and he shared great diet ideas with me. Within 5 months I was brought back to my proper BMI ratio and was fit. Having someone there with you to help and make you feel like your not alone is the best way to help someone with obesity or health problems in general. Being negative towards someone and calling them fat or toothpick when they clearly know how their bodies look more than anyone else isn't going to help them. It'll complicate things further by putting them into depression and throwing them into unhealthy eating habits and making them feel like they can't achieve anything like getting healthy.