Weight Needs to be Tackled in Childhood
to Avoid Lifelong Obesity

The air is thick in that way that the air around an indoor swimming pool can be. Six girls, none older than 11, frolic in the water, their laughter punctuated by the occasional yelp of ''Score!" as a small ball skitters through a basket dangling from the pool.

You wouldn't know it if you didn't ask, but those girls thrashing in the pool at Dorchester House are conscripts in the battle against the nation's epidemic of obesity. Their enlistment at such a young age serves as testament to what researchers have been preaching for a while now: In this fight, you can never begin too soon.

The war against the middle-aged bulge, scientists now understand, must begin decades earlier -- before the arrival even of adolescence. That's because, as a study from Tufts University proves, when it comes to being overweight, past is most definitely prologue.

The scientists found that girls who were pudgy as fourth-graders in Newton in the 1960s were nearly eight times more likely than their peers to be overweight as they crested middle age.

''It's quite astounding -- this shows that we can't afford to wait," said Vivien Morris, a Boston Medical Center nutrition specialist involved with the initiative that brought the girls to the health center's pool, a campaign designed to help heavy children shed pounds before they hurtle into adolescence.

There's no debate that the nation is mired in a crisis of weight: In the 1960s, about 4 percent of US children between the ages of 6 and 11 were overweight. By 2000, that figure had soared fourfold, according to federal disease trackers.

Doctors for years had suspected that the roots of obesity in women might be linked to when girls reached puberty. The theory went like this: If a girl had her first period earlier than expected, that increased her chances of being overweight as a woman.

Aviva Must, an obesity researcher at the Tufts School of Medicine, found instead that what was pivotal was a girl's weight before puberty and that being overweight during early childhood predisposed girls to having their first period sooner.

''There's been a misconception in the public and among some health professionals in thinking that girls who have early puberty are more likely to develop obesity," said Dr. Nicolas Stettler, a pediatric nutrition specialist at Children's Hospital of Philadelphia

Must's conclusion was an exercise in scientific sleuthing.

In the 1990s, Must stumbled upon the Newton Girls Study. It was a landmark research initiative conducted three decades earlier, with a Massachusetts General Hospital doctor tracking when 708 prepubescent girls had their first periods as well as other medical data, including the girls' height and weight.

After its original use, the study had been consigned to the dusty warrens of academia -- until Must learned of its existence. She decided to track down the now-grown women from the Newton study, ultimately locating 448 who provided health information.

The Tufts researcher found that in girls who experienced their first period before the age of 12, excessive weight was a probable trigger. The reasons for that aren't entirely clear, but scientists have theorized that deposits of fats may unleash a cascade of hormones alerting the body that it is capable of producing offspring.

Another theory: The excess calories consumed by an overweight girl cause her bones to grow faster and that, in turn, sends a signal that she can bear children .

So the girls who experienced early pubescence, Must concluded, tended to already be overweight. And those same women, once they reached their early 40s, were 7.7 times more likely than their peers to be overweight or obese.

The years before adolescence, then, emerge as a pivotal time for preventing a lifetime of excess weight -- for both biological and social reasons.

For one thing, younger children are more willing to listen to adults and less susceptible to peer pressure, making it easier to convey this message: ''There's nothing inherent about children that's incompatible with a natural diet abundant in fruit and vegetables. If that was the case, the human species would have died out years ago," said Dr. David Ludwig, a Children's Hospital Boston obesity specialist.

Still, obesity and nutrition specialists acknowledged, in a world of epicurean temptation -- soft drinks, salty snacks, fried foods -- it's not easy to get children to eat the right thing. That's why those specialists recommend that before parents place their children on a diet, they consult a pediatrician or nutritionist.

That's especially important for the parents of growing children, who must worry about going too far by giving too little.

''With kids," Must said, ''there's always the concern that severely restricted diets can restrict growth. With obesity, there are no magic bullets."

Which explains how, on a summer afternoon, Francisca Joseph and five other girls 8 to 11 years old found themselves in the pool at Dorchester House. This was serious fun with an equally serious purpose.

The girls were participating in something called Fantastic Kids. It started in spring 2004 as a pilot program for girls heavier than 85 percent of their peers -- sometimes weighing as much as an adult. This summer it expanded to include boys, with a mix of physical activity and classroom learning. There are games in the pool, weights to be lifted at the gym.

''And in the classroom, we have them tell us what they eat and measure the fat," said Salema Harold, a counselor in the program. ''They would say, 'Oh my God. Eww. That's how much fat we eat?' "

But does it make any difference? In a 12-week pilot study, the girls' weight was tracked. The result: Overall, weight gain stopped and some girls even began unloading a few pounds.

Francisca, who's 11 and lives in Dorchester, found out about Fantastic Kids when she came to Dorchester House with her aunt, whose baby needed a checkup. Francisca had been looking for a summer camp -- and for a way to lose some weight.

''I was tired of being big, and I couldn't find clothes to wear," Francisca said.

Now, she said, she knows to make better food choices (''If you want a candy, grab a fruit") and to down fewer soft drinks (''Now, I drink lots of water").

When she went to the doctor recently, she hopped on the scale.

Francisca, the doctor said, I have some news: You've lost weight.

Stephen Smith can be reached at stsmith@globe.com.