Basketball star LeBron James made $20 million more through endorsement deals, than his own $13 million annual salary playing for the NBA Miami Heat in 2012 alone. That may be great for his wallet, but not so great for the children who watched his commercials, a new study said.

A study published on Oct. 7 in Pediatrics found the bulk of the food sports stars are promoting, are unhealthy and pediatricians are concerned of the side effects it has on adolescents.

"Professional athletes wouldn't endorse tobacco today because it would be a liability for them," lead study author Marie Bragg, a doctoral candidate in psychology at Yale University, told the Globe and Mail. "We're hoping one day that the same would be true for unhealthy foods."

According to the study, 512 brands were endorsed by 100 top athletes and almost a quarter of them (122) were for food and beverages - 44 different brands in 2010, the year studied by researchers from Yale, Stanford, Duke and Harvard universities. Nearly 80 percent of the 49 food products were "energy-dense and nutrient-poor," and 93 percent of the 73 beverages got all of their calories from added sugar.

"The promotion of energy-dense, nutrient-poor products by some of the world's most physically fit and well-known athletes is an ironic combination that sends mixed messages about diet and health," Bragg said.

The study found that sports stars LeBron James, Peyton Manning and Serena Williams were the athletes most likely to have a sponsorship deal with a consumer company. James and Manning promoted the most caloric and nutrient-poor food.

"It would be ideal if athletes stopped promoting unhealthful food," Bragg added. "But that's a tall order given how much money is involved."

Meanwhile, the World Health Organization has called for policies limiting young people's exposure to food advertising.

"Professional athletes are in a unique position to use their highly visible status to promote healthy messages to youth," the researchers wrote.