Vogelvrij wrote: A very common aspect of eating disorders is that you try to lose weight by sporting. Gormur says he sports once a day, why would he need to do that more. Changing your life + eat habits is not about doing more sports, on the contrary.
He could try to change the sport. Instead of a cardiovascular sport, such as Jogging, Running, and to a lesser extent Tennis, try one in which bulk = advantage, such as Football (Which is mostly Cardio, but you need abs and leg muscles), weight lifting (best option for gaining bulk), Swimming (which is very cardio but requires strong overall body) or boxing (build that upper body).
While you can do any of those without "gaining bulk", muscle is an advantage, and you would want to eat those fatty, meaty foods and tons of grain to improve yourself.
But I agree more sport does not equal healthier and gain weight back. I'm quite scrawny myself, and when I was doing cardio workouts, I was actually told to stop because I was loosing weight faster than I could replace it with calories, instead of gaining any muscle.