In the HBO documentary, “Thin,” a fly-on-the-wall look at four patients checked into an eating-disorder clinic, one of them, Brittany, 15, tells her secret ritual: chewing and spitting. She and her mother would buy bags of candy, chew it, taste it and spit it out before swallowing. To Brittany, these episodes were nostalgic mother-daughter moments. The teen was bonding to her mother, who, not surprisingly, also has an eating disorder.

Brittany is by no means alone.

Which one is right: Is body weight due to genes -- or is it a consequence of lifestyle habits?

Two strong voices have come out, battling for each side of the debate. Most recently, New York Times reporter Gina Kolata wrote about the power of genes to dictate body weight. Her evidence comes from studies of:

• volunteers prodded by researchers to lose weight (all regained it by the end of the experiment)


• adopted children who mimicked their biological, not adoptive, parents’ weight range


• fraternal twins who varied in weight more than identical twins