You can't : We can guess, but it's health, genetics and nutrition.
Answered 8/16/2012
5.7k views
4 doctors weighed in across 3 answers
2 doctors weighed in across 2 answers
4 doctors weighed in across 2 answers
4 doctors weighed in across 2 answers
90,000 U.S. doctors in 147 specialties are here to answer your questions or offer you advice, prescriptions, and more.
Ask your question