Research from the University of Bristol indicates that adhering to a wholefood diet enables individuals to consume significantly larger quantities of food while actually reducing daily calorie intake. The study found that participants who followed an unprocessed food diet ate more than **50%** more food than those consuming ultra-processed foods (UPFs), yet averaged **330 fewer calories** daily.
Published in *The American Journal of Clinical Nutrition* on **March 15, 2024**, this study offers new insights into human dietary choices, suggesting that people possess an inherent “nutritional intelligence” that guides them toward healthier options when consuming food in its natural state.
Lead author, **Professor Jeff Brunstrom**, who specializes in experimental psychology, expressed enthusiasm about the findings. “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,” he stated.
The research reexamined data from a pivotal clinical trial led by **Dr. Kevin Hall** of the US National Institutes of Health. The original study established that exclusively consuming UPFs leads to excessive calorie intake and subsequent weight gain. However, the new analysis revealed fascinating dynamics concerning food choices among individuals consuming solely wholefoods.
Participants on the unprocessed diet frequently opted for fruits and vegetables, often consuming several hundred grams per meal, in contrast to higher-calorie options such as steak, pasta, and cream. This behavior resulted in a **57%** increase in the weight of food consumed by those following a wholefood diet.
In evaluating the nutritional quality of the participants’ meals, the researchers found that the variety and volume of fruits and vegetables provided essential vitamins and minerals. **Mark Schatzker**, co-author and food writer, noted, “Had participants eaten only the calorie-rich foods, our findings showed they would have fallen short on several essential vitamins and minerals, leading to micronutrient insufficiencies.” These deficiencies were effectively mitigated through the consumption of lower-calorie fruits and vegetables.
The researchers suggest this behavior reflects a phenomenon they term “micronutrient deleveraging,” whereby individuals prioritize nutrient-dense foods, such as fruits and vegetables, over energy-dense items. In contrast, UPFs often meet micronutrient needs, sometimes through fortification, while delivering high energy content. For example, calorie-rich French toast sticks and pancakes were found to be high in vitamin A, whereas carrots and spinach, which are lower in calories, contributed most of the vitamin A in the wholefood diet.
Dr. Annika Flynn, a Senior Research Associate, pointed out, “This raises the alarming possibility that UPFs deliver both high energy and micronutrients in one hit, potentially resulting in calorie overload.” She emphasized that this dynamic diminishes the beneficial trade-off between calories and micronutrient intake.
The findings urge a reconsideration of the impact of highly processed foods, which are pervasive in modern diets, on human behavior and decision-making regarding food choices. Professor Brunstrom underscored that overeating is not necessarily the primary issue; instead, the nutritional composition of food significantly influences dietary decisions. He explained, “Our research demonstrated that consumers on a wholefood diet actually ate far more than those on a processed food one. However, the nutritional make-up of food influences choices, and UPFs tend to steer individuals toward higher-calorie options.”
In related research conducted by the University of Bristol, altering the presentation of healthier dishes on menus encouraged more diners to select them, illustrating how promoting a sense of “healthy competition” can lead to better food choices.
This study was supported by the **National Institute for Health and Care Research** (NIHR) Bristol Biomedical Research Centre. For further information or to request interviews with the lead author or co-authors, please contact **Victoria Tagg**, News & Content Manager (Research) at the University of Bristol. The study is available online at the DOI: [http://doi.org/10.1016/j.ajcnut.2025.101183](http://doi.org/10.1016/j.ajcnut.2025.101183).
