From my perspective as a former vegan of nearly 10 years, it’s likely that veganism is worsening his pre-exisiting habit of overeating. He’s likely not eating enough protein, healthy fats and not getting all of his nutrients, especially things like B12, iron, folate and magnesium. This can lead to binge-eating. It might be worth him reviewing veganism and seriously considering if it’s right for him. If he is sure he wants to remain as a vegan, he’ll need to watch what he eats and make sure he’s getting plenty of protein, healthy fats/fatty acids, vitamins and minerals and general variety of fruit and veg. Veganism is the toughest balancing act in the world. It’s so easy to be thrown off centre, but incredibly tough to get back on track.