Dec. 13, 2012 -- A Columbia University researcher has calculated that NBA star LeBron James' ads might be responsible for selling a billion spoonfuls of sugar through his endorsement deals with Coca-Cola and McDonalds, and suggested James drop the ads that are largely aimed at his legion of young fans.

And since megastar Beyonce just signed a $50 million deal to be the face of Pepsi, social epidemiologist Abdul El-Sayed suggested she also reconsider.

"We all know Beyonce and Lebron aren't walking around eating McDonalds and drinking soda every day," El-Sayed told ABCNews.com. "They couldn't perform the way they perform night in and night out. The companies take full advantage of it."

El-Sayed penned an open letter to James earlier this week on The 2x2 Project, a health news website run by Columbia University's Mailman School of Public Health.

He broke down James' $16 million, six-year deal with Coca-Cola and determined that if Coca-Cola recoups its investment in him, at minimum, then he will have been responsible for having sold 54.4 million 20-ounce Sprites over the course of his contract.

"Now, each one of those 20-ounce Sprites has 16 spoons of sugar in it, so LeBron, you're responsible for selling over a billion spoons of sugar. Not to mention all of the McDonald's grease you're selling," El-Sayed wrote.

He cited a study in the journal Obesity Reports that found a clear link between watching advertisements for unhealthy foods and the number of snacks children ate on a daily basis. A second study, from the European Journal of Public Health, found that eliminating unhealthy advertising to children could reduce the obesity rate by as much as 18 percent.

"If you have someone as famous as Beyonce saying, 'I recognize these products are causing harm in society and I don't want to be a part of it,' it would raise the conversation about these products," El-Sayed said.

"If we were to take away these endorsements, in the end I would hope it would be the kind of thing where their sales wouldn't grow in the way they do and in the long term, these fall out as mainstays in our society."

Pepsi declined to comment. A representative of James referred comments to his sponsors. Representatives for Knowles, along with Coca-Cola and McDonald's, did not respond to ABCNews.com's request for comment.