Unprocessed diets lead to eating more foods but fewer calories
Key takeaways
- Reanalysis of a 2019 trial shows that people on a fully unprocessed diet ate about 57% more food by weight, yet 330 fewer calories than on a UPF diet.
- Whole-food diets naturally shift intake toward large volumes of fruits and vegetables, increasing micronutrient intake.
- The findings suggest excess calorie intake is driven less by overeating itself and more by how UPFs steer people toward energy-dense choices.
A reanalysis of data from a clinical trial on ultra-processed food (UPF) consumption reveals that people consuming a completely unprocessed diet ate about 57% more food (by weight) than participants eating UPFs, but consumed an average of 330 calories less per day.
The original trial was among the first to note that eating UPFs exclusively led to excessive calorie intake and weight gain.
According to the new analysis, participants who ate only whole foods consumed more fruit and vegetables, sometimes several hundred grams per meal, instead of eating higher-calorie foods like steak, pasta, and cream.
“Overeating is not necessarily the core problem,” says lead author Jeff Brunstrom, professor of Experimental Psychology at the University of Bristol, UK.
“Our research clearly demonstrated that consumers on a whole food diet actually ate far more than those on a processed food one. But the nutritional make-up of food is influencing choices, and it seems that UPFs are nudging people toward higher calorie options, which even in much lower quantities are likely to result in excess energy intake and in turn fuel obesity.”
Diet quality
The paper published in The American Journal of Clinical Nutrition also reveals that participants who ate whole foods had a more nutritious diet. The range and volumes of fruit and vegetables contained essential vitamins and minerals that participants would not have consumed by eating higher-calorie whole foods.
“Had participants eaten only the calorie-rich foods, our findings showed they would have fallen short on several essential vitamins and minerals and eventually developed micronutrient insufficiencies. Those micronutrient gaps were filled by lower-calorie fruits and vegetables,” explains study co-author Mark Schatzker, at McGill University, Canada.
Additionally, the authors suggest that participants eating only UPFs are also likely to meet micronutrient requirements, as foods are often fortified with nutrients like vitamins.
Participants on the whole food diet consumed more fruit and vegetables, resulting in higher food but lower calorie intake.For example, the foods with the highest vitamin A concentration were UPFs: French toast sticks and pancakes. In the unprocessed diet, participants mainly obtained this vitamin through carrots and spinach.
UPF vs. unprocessed foods
In the “seminal” clinical trial from 2019, led by Kevin Hall, Ph.D., then part of the National Institute of Health, 20 weight-stable adults consumed either an ultra-processed or unprocessed diet for two weeks, followed by the alternate diet for another two weeks.
The researchers designed meals to match the calories, energy density, macronutrients, sugar, sodium, and fiber provided. They instructed participants to consume as much or as little as they wanted.
On the UPF diet, participants had higher energy intake (an additional average of 508 kcal), with increased carbohydrate (280 kcal) and fat (230 kcal) intake, but similar protein intake.
While on the UPF diet, participants gained an average of 0.9 kg, while they lost 0.9 kg on the unprocessed diet.
Nutritional intelligence
The authors of the reanalysis claim their findings indicate that consumers have an inbuilt “nutritional intelligence” to achieve a well-balanced diet.
“It’s exciting to see when people are offered unprocessed options, they intuitively select foods that balance enjoyment, nutrition, and a sense of fullness, while still reducing overall energy intake,” says Brunstrom.
“Our dietary choices aren’t random — in fact, we seem to make much smarter decisions than previously assumed when foods are presented in their natural state.”
The authors also note that their study provides further insights into the effects of processed food consumption. Similarly, a 2025 clinical trial found that people on minimally processed diets lost twice as much weight as while on a UPF diet, as they consumed fewer calories.
Nutrition Insight recently explored the role of ingredient suppliers in bringing clarity to the debate on UPF healthiness and definitions.
These foods occupy a considerable share of supermarket shelves, and research increasingly links them to health issues. However, experts also caution against blanket policies and nutrition advice on these foods, as not all UPFs have the same poor nutritional value.
