A recent study from the National Institutes of Health found that people eating ultra-processed foods ate more calories and gained more weight than when they ate a minimally processed diet. The difference in weight gain even occurred when the meals provided to the volunteers in both the ultra-processed and minimally processed diets had the same number of calories and macronutrients.
This study considered foods “ultra-processed” if they had ingredients predominantly found in food manufacturing, such as hydrogenated oils, high-fructose corn syrup, flavoring agents and emulsifiers.
Previous studies had shown diets high in processed foods correlated to health problems. But, because none of the past studies randomly assigned people to eat specific foods and then measured the results, scientists could not 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 foods.
This is the first study to demonstrate causality — that ultra-processed foods cause people to eat too many calories and gain weight.
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 participants could eat as much or as little as they wanted.
On the ultra-processed diet, people ate about 500 calories more per day than they did on the unprocessed diet. They also ate faster on the ultra-processed diet and gained weight, whereas they lost weight on the unprocessed diet. Participants, on average, gained 0.9 kilograms, or 2 pounds, while they were on the ultra-processed diet and lost an equivalent amount on the unprocessed diet.