Whenever I've had a castrated male and an entire one at the same time they've both been fed the same food and I've never had any problems with weight management. If one of them starts to look a bit chubby or a bit skinny I adjust the quantity of their food slightly. I honestly think it's all about finding the food that suits your dog and don't believe there's anything special about all these breed specific foods, weight control foods etc. that warrants the extra money that manufacturers and vets charge for them.