It’s only a matter of time before heart disease “joins acne as an adolescent rite of passage,” said Dr. David L. Katz, syndicated columnist, television correspondent and authority on nutrition and weight control. Already, Katz said, he knows of a 17-year-old who underwent a triple bypass surgery.

Katz, the keynote speaker at the Shape Up Rhode Island kickoff celebration yesterday, described the signposts pointing to this troubling future. Children are eating too much of the wrong foods and not getting enough physical activity. As a result, type 2 diabetes — formerly a disease of middle age — is becoming prevalent among children.

Diabetes is such a strong predictor of heart disease that doctors are now advised to assume that their diabetic patients also have cardiovascular problems. So, Katz explained, with type 2 diabetes afflicting children, heart disease must be next.

Katz doesn’t believe government figures that say one child in five is obese. Based on his own observations, he thinks about half of all children are too fat. Meanwhile, obesity has already taken a measurable toll on adults, to the point that recent reductions in heart-disease deaths are at risk of being reversed.

Katz was perhaps preaching to the choir yesterday. The several hundred people in the audience at the Providence Place Cinemas had all signed up for a fitness program that has attracted 11,000 people to its third season. Each participant joins a team for a 12-week competition in which teams try to lose the most weight, exercise the most hours, or log the most pedometer steps — or any combination of those.

But while everyone there already wanted to get in shape, Katz saw their goals in broader terms. “This is an incredible movement,” he said. “This is a public health mission of the very first order.”

He likened efforts to fight obesity to piling sandbags to repair a broken levee. It takes a lot of sandbags to hold back the water. Each Shape Up RI team throws down a sandbag, and influences everyone who knows them to do the same.

“Let them be inspired by your example,” Katz said, “and you just may end up shaping up the world.”

Shape Up RI was founded in 2006 by a Rajiv Kumar, a Brown University medical student who was concerned about the preventable illnesses linked to obesity. The first 12-week competition attracted 1,800 participants. Last year 7,000 participated. This year, 11,000 have signed up. Both Governor Carcieri and Health Director David R. Gifford appeared at yesterday’s kickoff event.

Ray Rickman, Shape Up RI senior consultant, said that this year, Shape Up has teams from every city and town in Rhode Island. “Little Block Island has three teams of 11 each,” he said.

Among those in the audience was Colleen McMichael, 39, of Cumberland, leader of a nine-member team from a mothers’ group in Cumberland. “Let’s get healthy,” she says she told her pals, “because pool season is coming.”

First-time participants in Shape Up RI, they’re competing in both the exercise and weight-loss divisions. McMichael hopes to lose 30 pounds through walking and working out with a kettlebell (a large, heavy ball with a handle), and she thinks the team members “will help motivate each other.”

For more information go to www.shapeupri.org

ffreyer@projo.com