Ultra-processed foods contain substances you wouldn't find in your own kitchen, like high-fructose corn syrup, artificial flavor and color enhancers, anti-caking agents and emulsifiers. Dan Kitwood/Getty Images hide caption
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ultra-processed foods
Dr. Chris van Tulleken took part in a month-long experiment. He ate 80% of his calories from ultra-processed food. He explains what happened in his new book, Ultra-Processed People. Jonny Storey hide caption
An ultra-processed diet made this doctor sick. Now he's studying why
Foods classified as ultra-processed are those that have many added ingredients such as artificial coloring, added sugars, emulsifiers and preservatives. An apple may undergo minimal processing when it gets made into applesauce. But when it gets made into a shelf-stable apple pie or candy gummies with added sugars, colorings and flavorings, these foods are considered ultra-processed. Meredith Rizzo for NPR hide caption
An example of one of the study's ultra-processed lunches consists of quesadillas, refried beans and diet lemonade. Participants on this diet ate an average of 508 calories more per day and gained an average of 2 pounds over two weeks. Hall et al./Cell Metabolism hide caption