Reducing weighty obstacles

If a mother like Teneka Williams has to struggle to keep her daughter from sliding into obesity, America is in big trouble.

A couple of years ago, the Dorchester woman noticed her daughter Tiarra, now 9, gaining weight rapidly, jumping dress sizes in months. Worried, she served Tiarra smaller meals, encouraged her to be more active, banned soda. Then, after hearing a radio spot, she contacted the One Step Ahead Clinic at Children’s Hospital, which predominantly serves city kids who are Hispanic, or African-American, like Tiarra.

Williams is the kind of mother doctors at the clinic dream of. Usually, parents need convincing that their overweight kids have a problem, and they aren’t always ready to make changes. “Teneka has been incredible,’’ says Dr. Elsie Taveras, founder of the clinic.

The doctor saw additional reasons for Tiarra’s weight gain: The girl was watching too much television, which meant she was sedentary. It also meant she was exposed to countless ads hawking junk food. She was still drinking juice that contained as much sugar as Coke. The family was eating fried and fast food on busy nights.

Taveras assigned Williams and Tiarra a psychologist and a social worker to help them make healthier choices. Williams served more vegetables, baked chicken instead of frying it, replaced juice with water and low-fat milk. Unhealthy snacks gave way to rice cakes and bananas. Tiarra no longer watches commercial television.

The girl isn’t thrilled about these things. Sitting at a table outside Children’s on Friday, Tiarra, dressed in a green floral sundress, buried her bright face in her arms at the mention of rice cakes: “Ugh!’’ Still, she tries hard to stick to the plan.

But solving the obesity crisis, for this family and many others, isn’t just a matter of willpower. That is made distressingly clear by an HBO series called “The Weight of the Nation,’’ which airs May 14 and 15. Williams, Tiarra, and Taveras are featured in the documentary, and they’ll be part of a screening and panel discussion Monday night, timed to coincide with the launch of a new antiobesity effort called “Boston Moves for Health.’’ Nationally, about 32 percent of people are overweight or obese. In Boston, 40 to 45 percent of children are overweight or obese.

It seems like the whole world is set up to help girls like Tiarra gain weight. As the documentary points out, the childhood obesity rate has tripled in a generation. Kids spend hours they used to pass playing outside sitting at screens. The food industry spends $1.5 billion a year pushing junk to them. Schools offer precious little physical education, and lunches that are nutritionally bereft. And some in Congress want to keep it that way, arguing that marketing Lucky Charms as health food is a First Amendment right.

It takes superhuman effort for a family - especially a low-income, urban family - to resist all of this. How does a parent urge a child to play outside in an unsafe neighborhood? How to switch to healthier food if there’s precious little affordable and close by?

That is Williams’s problem, and one of the reasons why Tiarra - who had been losing weight steadily - has backslid some lately. Her closest grocery store is full of processed, sugary foods. Healthy chips cost a fortune, and Williams, a cosmetologist, and her husband, a custodian, don’t have a lot of money. She can get whole wheat pasta at her store, but not ground turkey. And sometimes life intrudes: Brown rice takes too long to cook, so she’s back to white.

“You can sit me down with a thousand nutritionists, but if I can’t afford it, or I don’t know how to prepare it, I’m going with the easy option,’’ Williams said. Still, she knows how lucky she is, compared to others. “It’s been a major challenge to me, and I have the help of all these people,’’ Williams said. “What about the people who don’t have that help?’’