A recent study led by scientists at the University of Bristol has found that adhering to an unprocessed food diet can significantly enhance nutritional intake while reducing overall calorie consumption. The research indicates that individuals who opt for a completely unprocessed diet not only consume over 50% more food by weight but also take in, on average, 330 fewer calories daily compared to those who primarily consume ultra-processed foods (UPFs).
The findings were published in The American Journal of Clinical Nutrition and suggest that people naturally gravitate towards a higher intake of fruits and vegetables when given unprocessed food options. This shift may aid in weight loss and promote better health. Lead author Jeff Brunstrom, a Professor of Experimental Psychology at the University of Bristol, emphasized that when presented with unprocessed choices, individuals tend to select foods that balance enjoyment, nutrition, and satiety, all while maintaining a lower energy intake.
The study revisited data from a pivotal clinical trial conducted by Dr. Kevin Hall of the National Institutes of Health, which originally highlighted how exclusive consumption of UPFs leads to excessive calorie intake and weight gain. The latest analysis reveals that participants consuming only whole foods significantly increased their intake of fruits and vegetables—often eating several hundred grams per meal—while shunning more calorically dense options such as rice, meat, and cream.
This dietary shift resulted in participants on the unprocessed diet consuming 57% more food by weight. The Bristol research team also assessed the nutritional quality of the participants’ diets, uncovering that the abundance of fruits and vegetables provided essential vitamins and minerals that would have otherwise been lacking if they had chosen only calorie-rich foods.
Co-author Mark Schatzker, a noted food writer, explained that had participants limited their diets to calorie-dense options, they would likely have fallen short on several vital nutrients. The study suggests a phenomenon described as “micronutrient deleveraging,” where humans instinctively prioritize foods rich in micronutrients—such as fruits and vegetables—over high-energy options.
In contrast, the study found that UPFs often provide both high energy and micronutrients, sometimes due to fortification. Notably, foods high in vitamin A, such as French toast sticks and pancakes, contributed to calorie intake while offering essential nutrients. In comparison, the majority of vitamin A in the unprocessed diet came from lower-calorie sources like carrots and spinach.
Dr. Annika Flynn, a Senior Research Associate at the University of Bristol, raised concerns regarding the implications of UPFs. She noted, “This raises the alarming possibility that UPFs deliver both high energy and micronutrients in one hit, which could result in calorie overload.” This suggests a detrimental effect on dietary choices, nudging individuals towards higher-calorie options that may contribute to obesity.
The research underscores the growing influence of processed foods on dietary habits and decision-making. Professor Brunstrom remarked, “Overeating is not necessarily the core problem. Our research clearly demonstrated that consumers on a wholefood diet actually ate far more than those on a processed food one.” Instead, the nutritional composition of food appears to play a critical role in influencing dietary choices.
Additionally, recent studies from the University of Bristol have revealed that simply altering the presentation of healthier dishes can encourage diners to make more nutritious choices. This notion of “healthy competition” in food selection is an avenue for promoting better eating habits.
The research received support from the National Institute for Health and Care Research (NIHR) Bristol Biomedical Research Centre. A paper detailing these findings, titled “Consuming an unprocessed diet reduces energy intake: A post-hoc analysis of an RCT reveals a role for human ‘nutritional intelligence,’” is available for further exploration.
For interviews with lead author Professor Jeff Brunstrom or co-author Mark Schatzker, or to request advance copies of the study, interested parties can reach out to Victoria Tagg, News & Content Manager at the University of Bristol, via email at [email protected]. The study will be accessible online once the embargo lifts.
