Medical Breakthroughs: What's your normal weight?

Like most women, 36-year-old Alessandra Valenzuela had a love-hate relationship with the scale, "in the past I would get on the scale every hour." She's also been fixated on attaining a specific weight.

"I was obsessed with a number on the scale. I wanna be 120. I want to be 125. I want to be 118. I want to break under 100. And then I would starve myself and I would not eat and I would lose a little weight and then go way back up."

So how do you determine your ideal weight? Dieticians we talked to say it's not healthy for women to try to go back to high school days and just because you're a certain height - one weight does not fit all. Lisa Richardson is a registered dietician.

"I always like to ask them to take a step back and relax and think about their tribe. Do they come from the polynesian type people, do they come from an ashley olsen type build. i always like people to take into account their heredity, their history. and so coming up with something more realistic." Registered dietician Lisa Richardson also suggests you consider your body composition, height, age, build and activity level. experts say you could weigh more than what many charts say is your ideal weight and still be healthy and happy.

Doctors at the University of Pennsylvania medical school say we all have a body weight thermostat -- a range within 10 to 20 percent -- we're naturally regulated to stay within. it's called a set point. Overeating swamps your regulatory system and your set point increases.