A recent study led by scientists at the University of Bristol has found that adhering to a wholefood diet can significantly increase fruit and vegetable consumption while reducing overall calorie intake. The study indicates that individuals who follow a diet comprised exclusively of unprocessed foods consume, on average, 330 fewer calories per day compared to those who eat ultra-processed foods (UPFs), despite eating over 50% more total food by weight.
Published in The American Journal of Clinical Nutrition on March 21, 2024, the research highlights how people naturally gravitate towards healthier options when presented with wholefoods, suggesting that humans possess an inherent “nutritional intelligence.” Lead author Jeff Brunstrom, a Professor of Experimental Psychology, emphasized the importance of offering unprocessed food options. “When people are given unprocessed choices, they intuitively select foods that balance enjoyment, nutrition, and a sense of fullness,” he stated.
The findings stem from a reanalysis of data from a clinical trial led by veteran researcher Dr. Kevin Hall of the National Institutes of Health. This earlier study had previously shown that consuming UPFs leads to excessive calorie consumption and weight gain. The new analysis reveals that those who restricted their diets to wholefoods consumed significantly larger quantities of fruits and vegetables, often exceeding several hundred grams per meal.
Participants on the unprocessed diet consumed 57% more food by weight, primarily focusing on lower-calorie options rather than higher-calorie staples such as meat and pasta. This shift in dietary choices not only contributed to weight management but also ensured that participants received essential vitamins and minerals that would have been lacking if they had opted for higher-calorie foods.
Co-author Mark Schatzker, an acclaimed food writer and researcher, noted that those consuming only calorie-rich foods would likely face deficiencies in essential nutrients. “Our findings showed they would have fallen short on several essential vitamins and minerals,” he explained, “but these gaps were filled by lower-calorie fruits and vegetables.”
The research also introduces the concept of “micronutrient deleveraging,” where individuals prioritize nutrient-dense fruits and vegetables over energy-dense options. In contrast, the study found that UPFs, often perceived as delivering “empty calories,” may actually provide both high energy and essential micronutrients, potentially leading to calorie overload. For instance, while calorie-rich foods like French toast sticks and pancakes were sources of vitamin A, those on a wholefood diet obtained this nutrient predominantly from carrots and spinach.
Dr. Annika Flynn, a Senior Research Associate at the University of Bristol, raised concerns regarding the implications of UPFs. “This raises the alarming possibility that UPFs deliver both high energy and micronutrients in one hit,” she warned, “which could result in calorie overload, as they effectively eliminate the beneficial trade-off between calories and micronutrients.”
The research contributes to a broader understanding of how highly processed foods affect dietary choices and health outcomes. Brunstrom highlighted the significance of nutritional composition in food choices, stating, “Overeating is not necessarily the core problem; rather, the nutritional makeup of food influences choices. UPFs tend to nudge individuals towards higher-calorie options, which can lead to excess energy intake and contribute to obesity.”
Additionally, a related study from the University of Bristol found that simply altering the order of healthier dishes on a menu encourages diners to select them. This highlights how fostering “healthy competition” can promote better dietary choices.
The study received support from the National Institute for Health and Care Research, a body dedicated to improving public health through research. For those interested in further details, the full study will be available online following the lifting of the publication embargo.
