A lot of kids grew up watching the popular Raven Symone on TV and in movies.  But Symone is not stick-thin like other teen stars.  She has a curvy figure.

Symone is a role model for girls like Khala Clay, who embraces her own curves and gets frustrated by the pressure to be a size 3 or 5.

"They have clothes for girls my size but they really don't, like they run out fast.  They have more clothes for skinny girls than they do thick girls, it's kind of aggravating," says Clay.

Now, add to that aggravation of a new study that shows exercise prevents obesity in white adolescent girls, but does not have the same effect for African American young women.

"There may be an ethnic difference between white and African American girls in the ability to burn fat and metabolize energy," says Rob Herzog, an exercise physiologist.

The study followed girls from the age of 12 to 14 and found that when calorie intake was the same, black girls were less sensitive to the effects of exercise than white girls.  Metabolically, they needed to exercise more to burn the same amount of calories.

Turns out this teen problems can become a very adult problem.  Four out of five  African American women are considered overweight leading to problems like heart disease and diabetes.

"Exercise is important.  Nutrition is important.  Trying to control body fat is important.  There are ways to do that effectively.  this study shows we want to be on our toes," adds Herzog.

That's motivation for Clay, who says when she isn't babysitting her cousin this summer, she will be stepping up her effort to get fit.

"I try to eat healthier and go outside and I run when I can and exercise a lot," says Clay.

The researchers in this study say they absolutely don't want to discourage any girls from exercising.  They say the results show African American girls may retain more fat accumulated during puberty and may need to exercise harder to get rid of it.

Read the study published in the Archives of Pediatrics & Adolescent Medicine.