I dont think it is catfood getting heavier on fat content, cats supposedly dont overeat, but I do disagree with that - I wouldn't have had overweight fosters if that had been the case - only one had a small appetite, the others would eat whenever you gave them food, and one was used to going eating in other peoples houses. My neighbours are very good at making animals overweight, they give lots of 'treats' and think cos it is fresh meat it is good for them. Lack of exercise is another factor - Ginger lived on the streets and was still overweight, cos his only exercise was walking to the next house on his 'list'.