As long as your weight is not really beyond the healthy range, if only your parents think you are fat, you can choose to communicate with your parents and tell them that thinness should not be everyone's pursuit. You have your own ideas, or try to appear in front of them as little as possible, secretly eat the dessert you bought, and try not to let your parents find out. You can show approval when they nag, tell them that you will lose weight and tell your parents to stop nagging, but you don't have to take action. Although it is good for parents to lose weight, if you are only slightly fat, or have a normal figure and don't pursue being particularly thin, then your figure should be decided by yourself.