Peyton Manning, LeBron James and Serena Williams are the top most influential U.S. athletes responsible for promoting and marketing unhealthy food, according to a research conducted by Marie Bragg from the Rudd Center for Food Policy and Obesity at Yale University in New Haven, Connecticut.

Top of the list is James of the NBA champion Miami Heat, who earns $42 million per year by endorsing McDonald's, Coca-Cola and other products; followed by Manning whose endorsements include Papa John's pizza and Oreo cookies and Serena takes the third place who has done ads for McDonald's and Oreo cookies.

Researchers said that when physically fit and well-known celebrities endorse junk food, fans tend to associate them with a sense of 'healthiness.'

"We see these people - they've obviously (reached the top) of sports achievement, they're obviously living a healthy lifestyle - and they're endorsing these foods. And that kind of lends an aura of healthfulness to these foods and beverages that they don't deserve," Emma Boyland, from the University of Liverpool in the UK told Reuters. "The message is really getting mixed up."

Bragg and her team arrived at the conclusion after looking into advertising deals for 100 top athletes in 2010, who endorsed over 512 brands, overall. Out of the brands, 62 food products were advertised including burgers, pizzas, cereals and cookies and 49 of the 62 brands were low in nutritional value but high in calories.

On the other hand, the athletes also endorsed 46 sports drinks, sodas and other beverages. All of the beverages were found to contain high levels of added sugar, which again is unhealthy.

"What stood out to us was the striking irony of the practice of having the world's most physically fit athletes endorsing these products," Bragg told Reuters, who led the study.

"Our ultimate hope would be that athletes reject the unhealthy endorsements or, at the very least, promote healthy foods," Bragg told NBC news. "These athletes have an opportunity to work with parents. Instead, they're promoting really unhealthy foods."

The alarming find of the study was that most of these advertisements were viewed by teenagers rather than adults during 2010.

"We know that children and (teens) are really affected by this type of thing," Boyland said. "We know that influences the type of foods they choose and they eat."

Bragg recommends that parents should be aware of all products advertised for children.

"Just because they're athletes doesn't mean that what they're endorsing is healthy," Bragg said

Kathleen Keller from The Pennsylvania State University in University Park states that preventing children from watching ads on television will not be enough to stop them from buying such food products because ads are all over the place. Instead, parents should explain to children how advertisements work.

"Within your home you can really teach your kids from a young age about what the purpose of marketing is, what the purpose of advertising is," Keller told Reuters.

The finding has been published in Journal Pediatrics.