Which came first: the chicken or the egg? That question has been stumping people for millennia. In fact, in the 4th century B.C. the philosopher Aristotle wrote, "There could not have been a first egg to give a beginning to birds, or there would have been a first bird which gave a beginning to eggs."

Only with evolution did we learn that the chicken came from some not-quite-a-chicken predecessor, all the way back to the first living cell.

Seems there's a faulty appetite regulator in the brains of obese teens. The question is: Did the broken regulator cause the excess weight, or is it a result of it?

As with the chicken and the egg, which came first? Well, we don't know, but realizing there's a broken food regulator provides a new understanding of the challenges obese teens face in achieving a healthy weight.

A study presented at the annual meeting of the Radiological Society of North America makes it clear that the 20.5 percent of 12-to-19-year-olds in the U.S. who are obese have measurable changes in the appetite-, impulse-, and reward-regulating centers of their brain.

Obesity affects the brain's amygdala, hippocampus, thalamus, bilateral hypothalamus and more. Helping teens attain a healthy weight means dealing with all of that.

It takes a team to help teens reset their brains: an exercise physiologist/coach; a nutritionist; a yoga or meditation instructor, plus cognitive behavioral therapy.

That can provide the tools needed to establish impulse control and help a teen recognize when enough food is enough.