Will neutering my dog make her fat?
No if you keep him or her on a healthy diet and if you don't overfeed.
What dog do you have? Some breeds pugs for example are more prone to weight gaining than others so they can become overweight regardless of neutering if they are feed improperly like the poster above said.
He's a Terrier mix, thanks for the replies
Honestly I've never seen an overweight terrier!