How do I get my husband to stop buying fast food?

My husband is a big man, and recently we have been trying to loose weight together. Not only because he is big but because I want him to be healthy. Lately he has been lying to me a lot about his purchases. Today I asked him what he bought while I was away from home and he insisted on nothing. But I had already spotted the spot on his shirt. I went as far as to smelling it, and it was food. Later he admitted it was Carl's JR. Burrito. But to cover it up he said they were for me. This is becoming a problem because IDK how to tell him he needs to stop eating fast food, i have tried before and It always comes out as fat. Any Ideas?