For people who choose to follow a diet consisting of unprocessed foods, research suggests that this shift can affect food choices in surprising ways. Instead of reaching for higher-calorie whole foods like rice, meat and butter, people naturally tend to eat much larger amounts of fruits and vegetables. This change alone can contribute to weight loss without the need to consciously reduce calories.
A study led by researchers at the University of Bristol and involving leading US nutrition experts found that participants who ate only unprocessed foods consumed more than 50 percent more food (by weight) than those who ate only ultra-processed foods. Nevertheless, their daily calorie intake was on average around 330 calories lower.
An Innate Ability to Balance Nutrition and Energy
The findings, published in the American Journal of Clinical Nutrition, offer new insights into the way people make food choices. The findings support the notion that humans have an innate “nutritional intelligence” that helps them maintain a balanced diet. This nutritional intelligence is reflected in the fact that in many cases individuals instinctively prefer foods that provide important nutrients while limiting consumption of less healthy options. This is not just a conscious weighing of calories or macronutrients, but a more subtle, intuitive ability linked to biological and psychological mechanisms. For example, taste preferences, feelings of satiety or even emotional reactions to certain foods could provide clues as to which foods the body needs. This instinct seems to work best when food is consumed in its natural form and can be disrupted by modern fast food environments.
Lead author Jeff Brunstrom, Professor of Experimental Psychology at the University of Bristol, said: “It is exciting to see that when people are presented with unprocessed options, they intuitively choose foods that balance pleasure, nutrition and satiety while reducing overall energy intake. Our dietary choices are not random – in fact, we seem to make much smarter choices than previously thought when food is offered in its natural state.”
Review of a Landmark Study on Processed Foods
The research involved a new analysis of data from a landmark clinical trial led by Dr. Kevin Hall, a longtime researcher at the U.S. National Institutes of Health. This original study showed that a diet consisting entirely of highly processed foods leads to overeating and weight gain. Such foods are highly processed industrially and typically contain many additives. This is not just a matter of simply cooking or chopping food, but products consisting of refined ingredients, preservatives, colorings, flavorings, emulsifiers and other chemical additives. Their regular consumption has been linked to obesity, cardiovascular disease, type 2 diabetes and other health problems.
The new analysis took a closer look at why people who ate only whole foods consumed much larger portions of certain foods and yet consumed fewer calories overall. The participants in the unprocessed diet consistently filled their meals with fruits and vegetables, sometimes eating several hundred grams at a time. They tended to avoid higher calorie foods such as steak, pasta and cream. As a result, people who ate whole foods consumed 57 percent more food overall.
Fruit and Vegetables fill Nutritional Gaps
The researchers also assessed how nutritious the diet was. They found that the variety and quantity of fruit and vegetables provided important vitamins and minerals that the participants would have lacked if they had only eaten higher-calorie whole foods.
Study co-author Mark Schatzker, author of “The Dorrito Effect” and “The End of Craving”, explained: “According to our results, if the participants had only eaten high-calorie foods, they would have been deficient in several important vitamins and minerals and eventually developed micronutrient deficiencies. These micronutrient gaps were filled by lower calorie fruits and vegetables.”
The researchers believe this behavior reflects a process they call “micronutrient deleveraging.” Simply put, people seem to prefer foods that are rich in vitamins and minerals, such as fruits and vegetables, even if it means eating less energy-dense options.
Why Highly Processed Foods Change the Equation
Highly processed foods led to a very different result. Although they are often referred to as ’empty calories’, the study found that they can meet micronutrient requirements, mainly due to their fortification with vitamins. For example, high-calorie foods such as French toast and pancakes were among the best sources of vitamin A. In the unprocessed diet, vitamin A came mainly from carrots and spinach, which provide far fewer calories.
According to study co-author Dr. Annika Flynn, Senior Research Associate at the University of Bristol, “This raises the alarming possibility that highly processed foods provide both high energy and micronutrients at once, which could lead to calorie overload by effectively nullifying the beneficial trade-off between calories and micronutrients.”
She added that whole foods restore this balance by encouraging competition between nutrient-dense, lower-calorie foods and higher-energy options. This helps people to choose fruits and vegetables rather than foods like pasta and meat.
Processed Foods and Modern Eating Behaviors
The findings offer further insight into how the widespread consumption of highly processed foods can influence behavior and decision-making. According to the researchers, overeating in itself may not be the main problem.
Prof. Brunstrom explained: “Overeating is not necessarily the core problem. In fact, our research has clearly shown that consumers who eat whole foods actually eat far more than those who eat processed foods. But the nutritional composition of foods influences choice, and it appears that highly processed products steer people towards higher calorie options, which even in much smaller quantities lead to excessive energy intake and in turn promote obesity.”
Related research from the University of Bristol has shown that even small adjustments in the environment or food offerings can have a significant impact on people’s choices. For example, the way products are presented, their placement in the supermarket or even the size of portions on offer can lead people to choose healthier options more often. These findings support the assumption that diet is not only controlled by knowledge or conscious planning, but is also strongly influenced by subtle, often unconscious cues in the environment. Even minimal changes – such as placing fruit and vegetables at eye level or presenting healthy snacks in a more attractive way – can therefore improve dietary decisions without people having to be actively “persuaded”. In a separate study, simply changing the order of healthier, more environmentally friendly dishes on a weekly menu led to more guests choosing these dishes.