Bert and Ernie jump rope and munch apples and carrots, and Cookie Monster has his namesake treat once a week, not every day. Can a Muppets mini-makeover improve kids’ health, too?

A three-year experiment in South America suggests it can. Now, the Sesame Street project is coming to the United States.

Already, a test run in a New York City preschool has seen results: Four-year-old Jahmeice Strowder got her mom to make cauliflower for the first time in her life. A classmate, Bryson Payne, bugged his dad for a banana every morning and more salads. A parent brought home a loaf of bread instead of Doritos.

“What we created, I believe, is a culture” of healthy eating to fight a “toxic environment” of junk food and too little exercise, said Dr. Valentin Fuster, a cardiologist at New York’s Mount Sinai Hospital.

Six years ago, he started working with Sesame Workshop, producers of television’s Sesame Street, on a project aimed at 3-to-5-year-olds.

“At that age they pay attention to everything” and habits can be changed, he said.

The need is clear: A third of U.S. children and teens are obese or overweight. Many don’t get enough exercise, and a recent study found that kids’ fitness has declined worldwide. They’re at high risk for heart and other problems later in life.

“The focus is younger and younger” to try to prevent this, said Dr. Stephen Daniels, a University of Colorado pediatrician and a spokesman for the American Heart Association. The group’s annual conference in November featured Fuster’s experiment as one of the year’s top achievements in heart disease prevention.

For Sesame Street, the project offered a chance to improve the lives of young viewers and give a makeover to certain Muppets.

“While Cookie Monster is an engaging figure, we felt there was an opportunity there to really model healthy eating,” said Jorge Baxter, regional director for Latin America for Sesame Workshop.

The new message is that certain things like cookies are “something you can eat sometimes, but there are some foods that you can eat all the time,” like vegetables, he said. The healthy messages have been gradually incorporated into the television show, and its producers even made a doctor Muppet — Dr. Ruster (pronounced “Rooster”) — in Fuster’s image for the preschool project.

It launched in Colombia because U.S. schools that Fuster approached years ago were reluctant, but a wealthy family’s foundation was willing to sponsor the experiment in Bogota.

It involved 1,216 children and 928 parents from 14 preschools. Some were given the program and others served as a comparison group.

Kids had training on healthy habits and how the body works for an hour a day for five months using Sesame Workshop-produced videos, a board game (the “heart game”), songs, posters and activities. Parents were involved through take-home assignments and workshops that focused on overcoming barriers to good food and exercise. For example, in areas with poor access to parks or play spaces, parents were coached to encourage kids to use stairs instead of elevators and to walk instead of taking a bus.

Children’s weight and exercise habits were measured at the start and 1 1/2 and 3 years later. Although many moved or dropped out by the time the study ended, researchers documented a significant increase in knowledge, attitude and health habit scores among kids in the program versus the comparison group.

The proportion of children at a healthy weight increased from 62 percent at the start to 75 percent at three years for those in the program. Ironically, in Colombia, that mostly meant that more undernourished kids grew to reach a healthy weight.

In New York, where the program plans to launch in several early childhood and Head Start programs this spring and fall, project leaders will have to tackle under- and overweight kids.

“A lot of the kids are from low-income families, shelters,” and many have poor access to healthy foods, said Rachael Lynch, director of educational services for an Episcopal Social Services preschool, The Learning Center, in Harlem. “It’s a mecca for fast food around here. We’re trying to get them to walk past the Chinese food or pizza or McDonald’s, to go home and make something.”

Her preschool tested the Sesame Street project last summer and “it really took off” with kids and parents, she said.

“They love it. The kids relate, I can’t stress it enough,” to the Sesame Street characters, she said.

The program had kids work in a nearby community garden one day a week to learn about growing vegetables. They had a “mystery food box” to reach inside, feel and guess the contents, then use what they found to make a healthy snack such as smoothies, fruit salads, microwaved baked apples and apple dip.

Children took home a “weekend update” to list and draw pictures of what they ate. Parents were asked to sign it to encourage an adult focus on healthy meals.

Kateshia Strowder said the program had a big impact on her and her daughter, Jahmeice.

“We’d be in the grocery store and she would name every vegetable. It’s amazing. Brussels sprouts — she likes it. Cabbage — she likes it,” Strowder said. “I’m not a vegetable eater, to be honest. But I had to learn to do those things for her.”

Donte Payne said the same for his son, Bryson, a 4-year-old who also was in the Harlem program.

“It made him more interested in eating more healthy things,” Payne said. “He became very interested in salads. He loves salad now.”

In Colombia, the program is now expanding to about 20,000 children, and in Spain, a project is starting in Madrid. In New York, a foundation Fuster runs at Mount Sinai will sponsor the U.S. launch, aided by private donors.

Dr. Jaime Cespedes, a pediatric and heart specialist who helped lead the project in Colombia believes it will succeed wherever it is tried.

“Sesame knows kids, knows media and how to communicate the messages,” he said. “When you get the kids to deliver the message to the family, change will come.”