In the past, it has been a tricky area to study as making direct correlations can be challenging. This is the first controlled, randomized study to directly compare the differences in people’s calorie consumption and weight gain on an unprocessed food diet versus one that is ultra-processed.
The researchers discovered that even when both diets were perfectly matched in amounts of fats, sugars, salt, calories, and carbohydrates, people simply ate more food and gained more weight when eating a diet of ultra-processed foods.
They reached their findings after studying healthy volunteers who stayed at the National Institutes of Health’s Metabolical Clinical Research Unit for one month. They were given one type of diet for two weeks and then switched to the other one for a further two weeks.
Regardless of which diet they were given, they had three meals a day, along with access to water and snacks that were either processed or unprocessed depending on which group they were in. They were instructed to eat as much food as they wanted, and researchers measured the quantities of food they consumed.
Just what was considered ultra-processed food for the purposes of the study? At breakfast, for example, participants might eat Honey Nut Cheerios cereal with whole milk that had added fiber, or a packaged blueberry muffin with margarine.
In contrast, an unprocessed breakfast might consist of apple slices with fresh lemon juice and plain Greek yogurt mixed with strawberries, walnuts, and bananas, with some olive oil and salt to make it match the processed breakfast.
The participants reported that the taste of both diets was good and that they felt satisfied with their meals, which removed food preference as a factor in comparing the diets.
The individuals studied consumed 508 calories more per day on the days they got processed food compared to the days they were given unprocessed food. They gained an average of two pounds on the two weeks they were on the processed diet, whereas they actually lost two pounds on average during the two weeks they were on the unprocessed diet. Likewise, they gained body fat during the ultra-processed phase and lost it during the unprocessed phase.
Interestingly, metabolic tests showed that people actually expended more energy while they ate the ultra-processed diet, but it was not enough to compensate for the higher number of calories they were consuming. Other measures of health did not show significant differences, such as blood glucose or liver fat.
What is it about ultra-processed food that makes people gain weight?
Although the study didn’t uncover a specific reason behind this effect, the researchers believe that there may be something about the texture of ultra-processed food that makes people eat faster as they noted the people in this group consumed their meals more quickly. They say that eating fast might not give your body enough time to realize that you’re full, leading to overeating.
The researchers noted that factors like cost and convenience didn’t come into play during the study as participants had all their meals prepared for them. Many people turn to ultra-processed foods because they lack the resources to prepare unprocessed meals, and this is an even bigger factor behind obesity and related health problems that warrants further exploration.
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