Cats are cats and that means they're skilled manipulators.
On the food front, how would you like it if the only food on offer was spam, spam spam? Get a range of brands for him. Supermarkets are helpful because they have different offers. Everyday give him some premium stuff he likes and some average stuff he'll eat if he's hungry.
He should get a max of 4 packs a day, but that assumes he eats it all. Give him smaller portions. Try a big breakfast, a big evening tea and a smaller portion for dinner and supper.
Just because he seems to be begging for food doesn't mean he's hungry. He could just be bored and be lookinig for attention and affection.
Also find out what your cat does. If he's a house cat he probably won't be getting much exercise unless you make a point of playing with him. If he's bored then all he'll do is eat, sleep, eat.
Hope that helps.