Usually, What's attractive is healthy, And what's healthy is good (duh). Usually why people don't find obese people attractive is because being overweight is EXTREMELY unhealthy and can shave decades off your life. Other things that men find attractive such as big breasts and butt are attractive because they are indicators of a woman who is good for childbirth and muscles are attractive to women because they indicate that said man is very physically capable. Acne and other unclean things are indicators that this person doesn't take very good care of their skin so it is found unattractive. All in all whats attractive is healthy and whats unattractive is unhealthy and if you won't do it to increase your chances of getting a significant other do it for your health.