Japan has it somewhat easy with their food. Low sugar and animal fat, usually very cheap fish...If you avoid junk food and do some sports it should be enough.
But the bigger problem (I think) are these super artificial beauty standards of doll-like women that might as well be robots.
Also being skinny can be nice, same with slightly chubby. Really depends on the body type. Just don't go all twitter dumb with "my 400kg are beautiful, sleep with me or you are racist"