Do people eat less on unprocessed diets? The answer is…it depends.
18 February 2026
A recent study published in the American Journal of Clinical Nutrition (read the study) explored why people appear to consume fewer calories when eating an unprocessed diet compared with an ultra-processed diet. The analysis used data from a well-known earlier clinical trial¹ in which participants were provided either an ‘ultra-processed’ or an ‘unprocessed’ diet for two weeks each and were allowed to eat as much as they wished. In the original study, participants consumed around 500 additional calories (approximately 2,000 kJ) per day on the ultra-processed diet and gained weight, despite the meals being designed to be broadly similar in fat, sugar, fibre and sodium.
Key findings
According to the researchers, several factors may explain the difference in energy intake:
Lower energy density Participants consumed fewer calories/kilojoules on the unprocessed diet largely because the foods were less energy dense. Unprocessed meals contained more foods such as fruit and vegetables, which are high in water and fibre, more bulky, and lower in calories/kilojoules per gram. Participants actually ate more food by weight on the unprocessed diet, but because the food contained fewer calories/kilojoules per gram, total energy intake was lower. In simple terms: more food volume, fewer calories/kilojoules.
Fat and carbohydrate combinations The study also found that meals containing a more even combination of fat and carbohydrate were associated with higher energy intake. The authors suggest that many ultra-processed foods contain this combination (for example pastries, snack foods and some ready meals), which may make foods more rewarding and encourage greater consumption. Unprocessed meals were less likely to contain this balance, which may have contributed to lower intake.
Meeting nutrient needs Participants on the unprocessed diet tended to select foods rich in vitamins and minerals, particularly fruit and vegetables. These foods provide micronutrients while contributing relatively fewer calories/kilojoules. The authors proposed a theoretical concept they describe as ‘micronutrient deleveraging’, suggesting that people may subconsciously select foods that help meet nutrient needs without increasing energy intake.
Overall conclusion
The study suggests that lower energy intake on unprocessed diets may be explained by a combination of lower energy density, fewer highly rewarding fat-and-carbohydrate combinations, and the selection of nutrient-rich foods that are naturally less energy dense.
What does this mean?
The findings contribute to ongoing discussions around dietary patterns, food design and public health policy. However, the authors note that the analysis was exploratory and further research is needed before firm conclusions can be drawn. Importantly, the results may not be broadly generalisable to all processed foods. Many processed foods contribute significant micronutrients to the diet through fortification — for example breakfast cereals fortified with B vitamins, iron and other nutrients, often consumed with milk or fortified plant-based alternatives.
Limitations to keep in mind
This analysis was based on a small, short-term study involving only 20 participants, with each diet consumed for two weeks under highly controlled conditions. The analysis used existing data from the original intervention and proposes mechanisms that the initial trial was not specifically designed to test. As such, the findings should be interpreted as hypothesis-generating rather than definitive evidence of cause and effect.
¹ Hall KD et al. Ultra-processed diets cause excess calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metabolism. 2019.
