It's amazing how easily one can lose weight when you have no say in the food you eat. A few years ago, one of our dogs was 50lbs. We finally put him on a diet when he was so fat it had to struggle to scratch his own ear. We changed his food (and we do not feed our dogs any human food). At first he didn't like it and would not eat it. He didn't eat for a few days and finally he got hungry enough he that he begin eating his new food. He eventually went on to lose 10lbs. He still eats the same food to this day and has no problems reaching his ear now.
10lbs doesn't seem like very much, but he only weighed 50lbs. To put that in perspective, if I were to achieve the same kind of weight loss, I would drop down to 154lbs. That's 39lbs!
We are our own worst enemies when it comes to this stuff. I'm convinced this wouldn't be an issue if I had some superior being providing all my dietary needs and did not get a choice in what I eat.