My girl has had big problems with her weight since she had a various assortment of medical issues but this is the diet that has kept her at 1.1kgs since December..
1. A bowl of water fresh 2 times a day (she kicks stuff in it and doesnt use it anyway but t's better than having none. I hate bottles because they leak).
2. Once handful of nuggets. I use excel burgess with mint. They're C shaped and she goes through one handful for the whole day, maybe 2 days. I don't use meusli anymore. She ate all of it anyway but they had a terrible sugar:fibre ratio!
3. Breakfast veggies - a leaf of romaine lettuce, a cherry tomato, an inch of celery (sliced into bits), an inch of carrot, a single grape/blueberry/strawb top in exchange for a piggy kiss on the nose!
Dinner veggies - a leaf of romaine lettuce, a pinch of mixed salad leaves (the ruby type, watch for chives (a no-no), spinach (give rarely) and herby ones. You're best with just a simple mixed small leaf). Inch of carrot, inch of pepper, an 1/8th of an apple.
Cabbages aggravate her bloat and her chalky pee so she doesnt get it anymore unless I'm eating it for dinner so she might get an end once a month or something! Bananas aggravate her oral yeast infection so I dont give those anymore either.
4. Unlimited hay in a fat wodge on the floor of her cage. She will eat it, poop in it, lay in it, snooze in it, flatten it out.. and then I change it. I have meadow hay (she gets a handful once a week), she has the pets at home timmothy hay (which she doesnt mind) and I also mix it with the pets at home normal hay (much finer and sweeter smelling - she prefers this). I try to give timmothy hay as much as possible. The meadow hay is actually quite calcium rich so I dont give it to her much. I also have a stupid amount of it left. When I whittle it down I will be buying timmothy hay from the hay experts. Much better than pets at home!
Edit: I just thought, if he is looking bigger without actually weighing more, it could be gas making his tummy puff up! If his tummy is firm or sounds hollow when tapped (you need to get right in there and get you ear on the other side on his tummy).. then watch how much farty veggies you give him, brocolli/sprouts and cabbage are the culprits in my house! You dont need to cut them out, but maybe once a week if you suspect anything.