People naturally consume fewer calories when eating whole foods compared to ultra-processed foods, even when allowed to eat as much as they want, according to a new analysis of a 2019 clinical trial.
Researchers at the University of Bristol re-examined data from a study where 20 participants were given unrestricted access to either unprocessed or ultra-processed diets for two weeks each. The diets were then switched. The initial trial focused on the amount of extra energy consumed by those eating ultra-processed foods. This latest analysis, published in the American Journal of Clinical Nutrition, examined the specific food choices participants made within each diet and how those choices impacted their overall energy intake.
The analysis revealed that participants ate, on average, 50 percent more food when consuming unprocessed whole foods, yet still consumed approximately 330 fewer calories daily than when on the ultra-processed diet. Psychologist Jeff Brunstrom, from the University of Bristol, stated, “It’s exciting to see when people are offered unprocessed options they intuitively select foods that balance enjoyment, nutrition, and a sense of fullness, even as still reducing overall energy intake.”
The researchers suggest this points to an inherent “nutritional intelligence” that guides food choices when foods are in their natural state. They theorize that individuals prioritize micronutrient-rich foods, such as fruits and vegetables, when presented with unprocessed options. This aligns with some research suggesting the body instinctively seeks to balance calorie intake with essential vitamins and minerals.
Conversely, ultra-processed foods are thought to disrupt this natural ability. These foods are often energy-dense and fortified with vitamins and minerals, potentially leading to calorie overload without a corresponding intake of nutrients. Psychologist Annika Flynn, likewise from the University of Bristol, explained, “This raises the alarming possibility that UPFs deliver both high energy and micronutrients in one hit, which could result in calorie overload, because they effectively kill the beneficial trade-off between calories and micronutrients.”
The study highlighted that participants could freely choose what comprised their meals within the assigned diet. Researchers believe this freedom underscores the existence of this innate nutritional guidance system. According to study author Mark Schatzker, a food writer in residence at McGill University in Canada, had participants solely consumed the calorie-rich foods within their diets, they would have faced micronutrient deficiencies, which were avoided by incorporating lower-calorie fruits and vegetables.
The findings add to growing concerns about the health risks associated with ultra-processed foods, which have been linked to obesity and conditions like Parkinson’s disease, according to recent research. While ultra-processed foods offer convenience and extended shelf life, the study suggests they may be “nudging” individuals towards higher-calorie consumption.
Further research is planned to determine whether this “nutritional intelligence” is universal, innate, or influenced by social factors. The study emphasizes that weight management isn’t solely about portion control, but also about the quality of food consumed.
