I have no opinion on the foreign exchange student who lost massive amounts of weight while on his exchange program. However, I would like to relate my own exchange weight loss story as a data point:
I was an AFS student (from the US) to Austria in 1982-83. I lived with a family that owned a pastry (Konditorei) and bread (Baeckerei) bakery and two cafes (with the bakery and one cafe in the house), and I managed to lose 40-50 pounds in the 10 months I lived there (from a somewhat overweight 205 lbs to a very fit 160 lbs).
Torture? Starvation? No, I simply went from a typical sedentary, junk-food-filled American lifestyle to an active Austrian lifestyle. In the US, I drove everywhere, and I consumed an entire box of Fig Newtons when I got home from school in the afternoon (while watching Gilligan’s Isle).
In contrast, in Austria I walked and rode the bus everywhere, and had three meals a day plus maybe one piece of cake or other pastry. I can only imagine what it would have been like if the family had served vegan, not fat-filled meat-heavy Austrian, food.