Thin people can put themselves first

For five years, Anne Fletcher, a registered dietitian and the author of "Thin for Life." worked in an obesity clinic.

"So often the women I saw were people who refused to take time for themselves," she recalls. "Their whole lives were spent giving, giving, giving -- which women tend to do anyway, but it was really to a fault. Sometimes you need to put yourself first."

Thin women prioritize eating right, exercising regularly, and reducing stress -- all of which are conducive to staying slim. Fletcher confesses to missing the occasional Little League game to work out but contends that such behavior shouldn't induce guilt. Rather, it's about taking care of yourself. "When people take the reins, they realize that the solution to weight control is inside them, not in some magic potion or fad diet that their mother or sister is on."

Thin people have thin parents

And genes are only partially responsible. "Perhaps 30 percent of being thin is genetic -- the rest is environment," says James O. Hill, Ph.D., director of the Center for Human Nutrition at the University of Colorado Health Sciences Center, in Denver, and cofounder of the NWCR.

If you're raised playing sports and eating healthy, unprocessed foods, chances are you'll continue those habits into adulthood, significantly raising your odds of staying slim.

Holly Johnson, age 45, a co-owner of a Sarasota, Florida--based marketing and public-relations firm and the mother of an eight-year-old, describes her father as a "beanpole" and says her mother still weighs "within three pounds of what she did when she married my dad."