People who eat ultra-processed foods take in more calories and gain weight than when they eat a minimally processed diet, according to a new study. The difference occurred even though meals given to the volunteers in both the ultra-processed and minimally processed diets had the same calorie and macronutrient count.
This small-scale study is the first randomized controlled trial on the effects of ultra-processed foods as defined by the NOVA classification system. This system considers foods “ultra-processed” if they contain ingredients primarily found in industrial food production, such as hydrogenated oils, high fructose corn syrup, flavorings and emulsifiers.
Previous observational studies in large groups of people had shown associations between diets high in processed foods and health problems. But because none of the previous studies randomly gave people certain foods and then measured the results, scientists couldn't say for sure whether the processed foods were a problem on their own, or whether people eating them had health problems for other reasons, such as a lack of access to fresh food.
“Although we examined a small group, the results of this tightly controlled experiment showed a clear and consistent difference between the two diets,” said the study's lead author. “This is the first study to show causality – that ultra-processed foods cause people to eat too many calories and gain weight.”
For the study, 20 healthy adult volunteers, 10 men and 10 women, were recruited for a continuous month and provided meals of ultra-processed foods or meals of minimally processed foods on each diet in random order for two weeks. For example, an ultra-processed breakfast might consist of a bagel with cream cheese and turkey bacon, while the unprocessed breakfast was oatmeal with bananas, walnuts, and skim milk. The ultra-processed and unprocessed meals had the same amounts of calories, sugars, fiber, fat and carbohydrates, and the participants could eat as much or as little as they wanted.
On the ultra-processed diet, people ate about 500 more calories per day than on the unprocessed diet. They also ate faster on the ultra-processed diet and gained weight, while losing weight on the unprocessed diet. Participants gained an average of 0.9 kilograms or 2 pounds while on the ultra-processed diet and lost an equivalent amount on the unprocessed diet.
