Few parents go as far in influencing their children's diet as Michael Arnstein, the extreme-distance runner better known on YouTube as "the Fruitarian."

Arnstein practices a strict dietary subset of veganism in which he, and his family, consume only fruit, though he acknowledges his children probably sneak other foods while they're in school or at a friend's house.

However fruity Arnstein might seem to the average person, most American parents heavily supervise their children's meals, even well into the teenage years, a new study in Pediatrics shows. Moreover, two-thirds of parents insist their children stick to the "clean plate" dictum, an unwritten federal law stipulating that one must finish everything on one's dinner plate.

"I was surprised at some of the parent behaviors, like feeling that their children should clean their plates and not waste food," study author Katie Loth, a registered dietician, doctoral candidate and research assistant at the University of Minnesota in Minneapolis, told media. "In the 1950s, cleaning your plate meant something different. Portion sizes have gotten bigger over time, and if you encourage kids to rely on environmental indicators, like how much food is on their plates or the time of day, they'll lose the ability to rely on internal cues to know whether they're hungry or full."

Loth and other experts warn that such practices might prevent children from developing healthy eating habits as adults. The researchers grabbed data from two recent studies, one conducted in 2010 and another during 2009 and 2010, to analyze the behaviors of more than 2,200 teenagers and nearly 3,500 parents from Minnesota. The average age of the child was 14.4-years-old.

Researchers in the two studies had asked parents whether they ever pressured their children with affirming statements such as, "My child should always eat all of the food on his or her plate." The research also included a four-item "Pressure-to-Eat Subscale," by which investigators quantified how much pressure parents applied to their mealtime policies.

Not surprisingly, researchers found that parents more often told overweight children to eat less, while telling normal-weight children to eat more. But some parents encouraged their children to "clean" their plates, even if the child was overweight. Dieticians find this bit of information troubling given that childhood obesity, with a maelstrom of accompanying health risks, has doubled among children and tripled among adolescents during the past three decades. The U.S. Centers for Disease Control and Prevention says in 2010 one-third of children were overweight or obese, with approximately 18 percent of children ages 5-19 obese.

Dr. Elaine Schulte, a pediatrician at Cleveland Clinic Children's Hospital in Ohio, who was not involved in the study, commented to media. "Parents are doing way too much in controlling the way kids eat," Dr. Elaine Schulte, a general pediatrician at Cleveland Clinic Children's Hospital in Ohio who was not involved in the study."

Schulte said parents should supply their children with healthy food and advice, but should not dictate, lest they do more harm than good.