How is he? is he acting normal? lethargic? did something change? the recommended feeding amount at the back of dogfoods are just that...recommendations. the best way to see if he does need more food is to look at him. when you look above he should have a waist. at the sides you shouldn't be able to see his ribs but should be able to feel it. if you touch him and you have to search for his ribs then he might be eating too much. losing weight isn't necessarily a bad thing. what is he weighing now? my boy at 8 months weighs 21 kg and has a ton of energy!
others would advice you to "spice up" his food like adding Jogurt, meat, eggs, veggies. . hope this helps.