You don't see a lot of celebrities advertising kale - which is okay, kale is not all that healthy, but at least it has a health halo. Not so for soda and other sugary drinks, fast food and sweets, and those are among the most common food and beverage products endorsed by famous music personalities.

They are directly to blame for obesity, claims lead author Marie Bragg, PhD, assistant professor in the Department of Population Health at NYU Langone, in Pediatrics.

Unsurprisingly, Big Lettuce did not hire celebrities to do endorsements, nor did music stars endorse fruits, vegetables, or whole grains. Only one endorsed a natural food deemed healthy -pistachios - over a 14-year period covering dozens of advertisements. Yes, dozens.  

"Because of our nation's childhood and teenage obesity public health crises, it is important to raise awareness about how companies are using celebrities popular with these audiences to market their unhealthy products," said Bragg. "Research has already shown that food advertising leads to overeating, and the food industry spends $1.8 billion per year marketing to youth alone."

Study Methods: Identifying Pop Stars and their Endorsements

To identify popular music stars, the investigators went through Billboard Magazine's "Hot 100" song charts from 2013 and 2014. The researchers also verified their popularity and marketing appeal with teens by reviewing Teen Choice Award winners, and quantified the number of YouTube video views associated with the celebrities' food and nonalcoholic beverage brand endorsements.

The investigators then cataloged every endorsement between 2000 and 2014 using AdScope, an advertisement database that contains all forms of ads, including television, magazine, and radio. They also searched for official commercials or endorsements on YouTube and in media sources. Endorsements were defined to include a celebrity's participation in a concert sponsored by a product. 

After sorting the endorsements into different marketing categories, the authors found that 65 of 163 identified pop stars were associated with 57 different food and beverage brands. Food and nonalcoholic beverages were the second-largest endorsement category, comprising 18 percent of endorsements and ranking after consumer goods at 26 percent and ahead of retail at 11 percent.

To assess nutritional value of the endorsed food products, the investigators analyzed nutrition information on food labels using the Nutrient Profile Model (NPM), which has been used in other food marketing research studies and provides a score that represents nutrient content. Twenty-one out of 26 food products -- or 81 percent -- were deemed "nutrient poor."

The investigators determined a beverage's healthfulness by looking at calories from added sugar. Of 69 beverages endorsed, 49 or 71 percent were sugar-sweetened. Full-calorie soft drinks were the most commonly endorsed in the category. In contrast, water-related endorsements appeared only three times. 

Food and beverage marketing has been identified in a variety of epidemiologic and psychology studies as a significant environmental contributor to childhood obesity. In 2012, over one-third of children and adolescents were overweight or obese, according to the U.S. Centers for Disease Control and Prevention and the U.S. Public Health Service. Causation, meet correlation. 

Although many food and beverage companies have taken voluntary pledges not to target children under 12 years old with certain marketing, teens are not included.

The authors believe celebrities should use their images to be positive role models for foods, and stop promoting things just because they are paid. No word on if that should apply to academics as well.