Eating food that's ultra-processed — not just chips or cookies, but also things like breakfast cereal, deli meat, or canned fruit in syrup — makes people overeat and gain weight, compared with eating food that's unprocessed. That's according to a small randomized controlled trial published online May 16, 2019, by Cell Metabolism. It involved 20 men and women who stayed at a research facility for a month and were randomly assigned to one of two diets. One group was given ultra-processed foods (such as a breakfast of a bagel with cream cheese and turkey bacon), and the other group was fed unprocessed foods (such as a breakfast of oatmeal with bananas, walnuts, and skim milk). After two weeks, participants were switched to the opposite diets. Both diets were evenly matched for total calories, macronutrients, fiber, sugars, and sodium, and participants were allowed to eat as much or as little as they wanted. But they ate more calories when they were eating ultra-processed foods, compared with when they ate unprocessed foods, and they gained more weight on the ultra-processed diet. Why? It's not exactly clear, but researchers did find that appetite-suppressing hormones decreased and hunger hormones increased when people ate processed foods. Bottom line: Eat whole, unprocessed foods with as few ingredients as possible.
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