Pro athletes such as Peyton Manning and Serena Williams are often paid big fees to endorse a whole range of products. Now, a new study has found that the majority of the foods and drinks such athletes endorse is calorie-laden and unhealthy.

Researchers at the Rudd Center for Food Policy and Obesity at Yale University compiled a list of endorsement deals for the Top 100 athletes in the U.S., based on BusinessWeek’s 2010 Power 100 report. Of the 512 brand endorsements that same year, 122 were for food and beverage brands.

The researchers found that of the 62 food products high-ranking athletes endorsed, 49 were high in calories and low in nutritional value. Of the 46 sports drinks, sodas and beverages the athletes endorsed, for example, the calories in 43 of them came entirely from sugar.

The study, which will appear in the November issue of Pediatrics, also found that teens aged 12 to 17 were the demographic that viewed the greatest number of TV ads for athlete-endorsed food.

Most of the athletes who endorsed food and beverages were from the NBA, followed by the NFL, the study found. NBA star LeBron James had more food and beverage endorsements than any of the other athletes, followed by NFL quarterback Peyton Manning and tennis star Serena Williams.

Study author Marie Bragg, a doctoral candidate at Yale, says it's ironic that the most-physically fit and well-known athletes often promote food products with high calories and low nutrition.

She says it's a combination that "sends mixed messages about diet and health."

Bragg and her co-authors note that it was not so long ago that pro athletes, such as Babe Ruth, were happy to endorse cigarette brands – something that would never happen today. She says pro athletes should now give serious consideration to the health value of the food and drink products they are endorsing, and use their celebrity to promote healthy messages.

"Professional athletes have an important opportunity to promote the public's health, particularly for youth, by refusing endorsement contracts that involve promotion of energy-dense, nutrient-poor foods and beverages," the study authors conclude.