You shouldn't keep pestering people that won't listen.
Greg has an overweight coworker who has no interest in anything health-related that Greg tells him.
Greg wants his coworker to get healthier.
Greg asks his coworker if he wants to go out walking or for some physical activity whenever the chance arises.
Greg continues to tell his coworker about ways to improve his health and gives him books about it.
Greg's coworker gets more exercise from Greg including him and learns to enjoy it.
The coworker gets so annoyed with Greg that he completely cuts off their friendship.