Ultra-processed foods are defined as ready-to-eat foods with five or more ingredients that frequently include additives such as flavour-enhancers, stabilisers or preservatives.
The first of its kind, a trial assessed how ultra-processed food impacts appetite and diet compared with a comparison diet of minimally processed foods. In addition to eating far more calories when eating ultra-processed foods, the participants also put on significantly more weight than when they had the less processed foods.
The study involved 20 participants. Each diet was followed for 14 days before switching to the other diet. Both diets selected were of equal calorie content, however, participants were instructed to eat as much or as little of the diets that were available to them.
The ultra-processed foods in the study included breakfast cereals, canned ravioli, hot dogs and sweetened yoghurt. The minimally processed foods included oatmeal, salads, steamed vegetables and grilled chicken.
The meals were matched in terms of calories, sugar, carbohydrate, fat and fibre between the ultra-processed and minimally processed diets. Despite the available food being matched across these criteria, the participants consumed many calories from the ultra-processed foods. By contrast, the minimally processed foods seemed to provide a natural brake that prevented the participants from over-consuming calories.
The average extra 500 calories being consumed on the ultra-processed diet saw an average increase in weight of 0.9kg. By comparison, when they followed the minimally processed diet, the participants lost 0.9kg of body weight.
Lead researcher Dr Kevin Hall, from the National Institute of Diabetes and Digestive and Kidney Diseases, said: “I was surprised by the findings from this study, because I thought that if we matched the two diets for components like sugars, fat, carbohydrates, protein, and sodium, there wouldn’t be anything magical about the ultra-processed food that would cause people to eat more.
“But we found that, in fact, people ate many more calories on the ultra-processed diet, and this caused them to gain weight and body fat.”
The findings have been published in the Cell Metabolism journal.