In a landmark NIH trial, 20 adults ate about 500 more calories a day, and gained around 2 pounds in two weeks, when their meals were made from ultra-processed foods. When the same people switched to a diet of unprocessed foods, they lost the same amount of weight without being asked to eat less.
The study, led by NIDDK senior investigator Kevin D. Hall and published in Cell Metabolism in May 2019, was the first randomized controlled trial to test the direct effect of ultra-processed foods on calorie intake and body weight. Both diets offered the same amount of calories, sugar, fiber, fat, and sodium.
The first shift is in your appetite
When ultra-processed food leaves the plate, appetite signaling begins to look different. In Hall's trial, the appetite-suppressing hormone PYY rose and the hunger hormone ghrelin fell during the unprocessed diet, compared with the ultra-processed one. Harvard Health, in its coverage of the study, describes the same pattern, noting that appetite-suppressing hormones went down and hunger hormones went up when people were on the processed diet.
Participants also ate faster on the ultra-processed arm. According to NIH News in Health, people ate about 500 more calories each day on ultra-processed meals and gained about 2 pounds on average, while the less-processed diet led to about 2 pounds of loss. Nobody was told to restrict anything.
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The rough patch some people hit
Feeling better is not always immediate. Ashley Gearhardt, a clinical psychologist at the University of Michigan who studies overeating, is investigating whether cutting back on ultra-processed foods can trigger withdrawal-like symptoms. In the NIH article, she describes what she hears from people trying to change their diet.
"When I start to eat healthier, I feel so irritable and agitated. My cravings are so strong that I don't feel better. I feel worse," Gearhardt says, quoting the common reaction she gets from people who try to cut back.
She also puts the pull of these foods in blunt terms. "These ultra-processed, highly rewarding foods have way more in common with a cigarette than they do with an apple or an orange or black beans," Gearhardt told NIH News in Health.
What actually counts as ultra-processed
The NOVA classification, used in Hall's trial, sorts food by how much industrial processing it has gone through. Ultra-processed foods sit at the top of that scale, built with ingredients you would not typically keep in your kitchen, like hydrogenated oils, isolated proteins, and high-fructose corn syrup.
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A simpler shortcut comes from Alexandra DiFeliceantonio, a neuroscientist at Virginia Tech. "If you're standing in the grocery store, in one of the middle aisles, and the thing that you're holding is in a crinkly package, you're probably holding an ultra-processed food," she told NIH News in Health.
Carbonated soft drinks, chips, chicken nuggets, and packaged sausages sit firmly in that group. Whole fruits and vegetables, unprocessed meat and seafood, nuts, and legumes fall outside it. Even partial swaps can move the needle, and follow-up research has linked cutting ultra-processed food with more spontaneous weight loss.
Two weeks will not clear every craving. But even in that short window, the physiology starts to shift, and it happens without conventional dieting.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.