If you're dining with overweight friends, beware.

A small U.S. study had found that overweight children and teenagers eat more when they have a snack with an overweight friend rather than with a thinner peer.

Researchers from the State University of New York at Buffalo studied a group of 9 to 15-year-olds and found that all youngsters, regardless of their weight, tended to eat more when they snacked with a friend rather than a peer they did not know.

But the biggest calorie intakes were seen when an overweight child snacked with an overweight friend.

The findings, reported in the American Journal of Clinical Nutrition, highlight the role of friends' influence in how much children eat and, possibly, in their weight control.

Researcher Sarah-Jean Salvy, an assistant professor of pediatrics at the State University of New York, said it was not surprising that children eat more when they are with friends instead of strangers.

She told Reuters Health that the same pattern has been found in adults which can be partly explained by people being more self-conscious around strangers.

But this can also be partly explained as friends act as "permission-givers." "They set the norm for what is appropriate to do, or in this case eat," said Salvy.

For the study, Salvy and her colleagues had 23 overweight and 42 normal-weight children and teens spend 45 minutes with either a friend or an unfamiliar peer.

Each pair was given games, puzzles and books for entertainment, along with bowls of chips, cookies, carrots and grapes.

Overall, the researchers found that pairs of friends downed more calories than did unacquainted pairs and overweight friends consumed the most — 738 calories, on average, versus 444 calories when an overweight child was paired with normal-weight friend.

Normal-weight kids consumed an average of about 500 calories when paired with a friend, regardless of the friend's weight. Salvy said a recent study of adults found that people were more likely to gain weight over three decades if their same-sex friends were overweight or obese, suggesting a role for "social influence" in body weight.

When it comes to children and teens, it's known that many follow their friends' lead in deciding whether to smoke or drink.

Salvy said the current findings suggest that children' eating habits are also "largely determined by their social network."

The good side of that, according to Salvy, is that helping one child make healthy changes may end up influencing his or her friends as well.