There’s a free and easy technique that can help stave off excessive weight gain in childhood: Eat more slowly and stop eating when you’re no longer hungry. 

A new study published in the journal Pediatric Obesity details how researchers monitored the eating habits of 54 children ages 6 to 17 in Durango, Mexico for a year. One group was given this simple instruction: Take a bite, chew, and let 30 seconds pass before you take another bite. The other group did not wait between bites.

Over the course of a year, the children who were told to eat more slowly lost 3.4 to 4.8 percent of their weight; the other group gained 8.3 to 12.6 percent.

Researchers credit the results to the fact that kids who ate more slowly benefited from the “satiety reflex,” which is when the stomach tells the brain that it’s no longer hungry. The reflex takes about 15 minutes to activate, but kids — and adults — often scarf down meals in much less time than that. Geert Schmid-Schonbein, a study co-author and bioengineering professor at the Jacobs School of Engineering at UC San Diego, tells Yahoo Parenting that in addition to taking slow bites, it’s key that kids stop eating when they’re no longer hungry — before they feel stuffed. “You want to catch that feeling early on, long before you consume large amounts of calories,” says Schmid-Schonbein.

The idea that waiting 30 seconds between bites of food can have such a big impact on weight is encouraging in many ways. Besides being free and easy, it’s also a habit that can last a lifetime, unlike many quick-fix diets. Plus, you can stick with the foods you already enjoy. 

“You can adopt slow eating permanently,” Schmid-Schonbein says. “When a child learns this approach, they can teach it to their children years later — this is intended for life.”

Parents who want to try the technique with their own kids might make it a fun activity at first, which is just what the researchers did. They gave the kids who ate slowly 30-second hourglasses and told them to take a bite, turn over the hourglass and not bite again until the sand was emptied. “The hourglass made it more like a game,” said Pedro Cabrales, a bioengineering professor at the University of California, San Diego and a study coauthor. “We also noticed that the children kept each other accountable. If some forgot the hourglasses, the others would remind them.”

Incorporating slow eating into family mealtimes is a good idea too, because adults can potentially benefit from the practice as well. “The entire family should participate in making this change,” says Schmid-Schonbein, cautioning that the “clean your plate” tradition has no place in slow eating. “Have kids eat slow bites for 10-12 minutes, and when they have no more hunger and are ready to run off, let them go. When you don’t force them to eat more, they fall into a very natural cycle at every meal.”