Animal Welfare Professionals

What are dome reasons a dog who has never shown food aggression all of a sudden start? Are there things that can be done to put a stop to it? I have a 7 year old pit mix and 3 cats. The dog Thumper has all of a sudden started showing aggression towards the cats when I am eating or when he has treats such as his Kong toys. I want everyone to coexist peacefully like we had finally achieved! TIA!