What could help against big appetite?

Water protein fiber. You can fool your stomach into thinking it has food in it by keeping it full of water (not diet soda). Also you stay satisfied much longer after a meal if you concentrate on protein (meat, nuts, eggs, cheese) and cut out as many carbs (potatoes, rice, pasta, etc.) as you possibly can. These take longer to digest and therefore leave the stomach more slowly. Same with fiber (bran, vegs pgf).