More fibro as: frut/vegies, natural oats breakfast, psyllium husk, lecitine as supplement (other supplements are in health Food Shops). Give him more mineral water to drink. Massage of stomach and some excesize. Dry plums on daily basis. Drink carrot/beetroot/selery juice as a mixture. Eat more yogurt/buttermilk. Try to think what is the cause of constipation? Is he lacking of fibro/water or may be some serious bowel problem (gastroscopy can help).