It will be better to adopt dialectical theory. Tell him straight away that you are too fat, and then discuss the benefits of being fat, such as being broad-minded and kind, and encourage him mentally. Then point out that being too fat will make you sick, such as hyperlipidemia and high blood pressure, and then ask him if he feels sick. He said yes, strike while the iron is hot, tell him to avoid eating, how to lose weight, and have perseverance. The whole process should be sincere, don't talk big or use irritating words (such as pigs), and listen to each other's reactions. There should be no problem.