It is not a problem to overeat and become fat during puberty,
because adolescents grow into their weight.
This myth is very, very dangerous, and may decide if you go
through yo-yo dieting all your life, or if you become a
consistently thin adult. Adolescents only grow into their weight
before their main growth spurt. If they are past their main growth
spurt, they will not grow into their weight. If a 15 year-old,
almost fully developed, decides that he'll just grow into his
weight, and eats heavily, he'll become obese. During adolescence,
the number of adipose cells, which hold fat, become set in stone.
If you have five trillion cells while maturing, you will have five
trillion for the rest of your life. This is why the odds against an
obese teen becoming a normal-weight adult is 28 to 1. It is
possible, but it is very, very difficult. Adolescence is not a good
time to put on weight.