A study observed how, with equal calories and nutrients, a meal made from minimally processed foods and one made from highly processed foods generate different responses at the metabolic level and in terms of brain activity.
A meal prepared with fresh, minimally processed food and a meal made up of ultra-processed foods, with the same caloric and nutritional intake, generate different metabolic responses and activity in the brain's reward system.
This is what was observed in a study by the Fralin Biomedical Research Institute at Virginia Tech, published in Nature Metabolism: two meals with the same carbohydrates, fats, proteins, water, calories, salt and weight, but differing in their level of processing, produced different effects on the body at the metabolic and cerebral level.
The study was conducted on 57 adults aged between 18 and 45. Both meals administered were 300 calories. The highly processed meal included a bite of a peanut butter and jam sandwich, sliced turkey, vegetable chips, a biscuit, cereal, instant mashed potatoes and some water. The minimally processed meal included sliced banana, dried cranberries, cheese and an egg. The composition of carbohydrates, fats, proteins, calories, water and salt was identical.
Blood samples were taken from participants immediately after the meal, and then a further six times over the following three hours. The researchers measured post-prandial metabolism — the set of chemical reactions and physiological processes that occur in the human body after the ingestion and digestion of a meal — including the insulin response, energy expenditure and carbohydrate oxidation, the process by which sugars are used to produce energy.
The scientists observed that ultra-processed meals caused the body to release more insulin and burn more energy, while simultaneously using fewer carbohydrates as an energy source. "We were surprised to find differences in every single metabolic parameter," explained Zach Hutelin, the study's first author. "What we observed with ultra-processed foods is that the insulin response was much higher and blood sugar remained slightly elevated for a longer period of time." As is well known, chronically elevated blood sugar levels increase the risk of conditions such as diabetes.
Ultra-processed meals also triggered different responses in the part of the brain involved in motivation and reward. The scientists investigated whether the metabolic response to the meals was linked to the brain's response to visual food cues. Participants viewed images of highly processed and minimally processed foods with equivalent nutritional characteristics, while undergoing functional magnetic resonance imaging. As they looked at each food, participants indicated how much they would be willing to pay for it. This allowed the researchers to compare the subjective value participants assigned to the foods with their brain activity.
One significant finding concerned the ventral striatum and the nucleus accumbens, brain areas involved in processes of learning, motivation and reward. The differences in the way participants metabolised carbohydrates for energy after the different types of meal were found to correlate with differences in the brain's response to images of food. Although participants did not report being willing to pay more for ultra-processed foods than for minimally processed ones, the findings suggest that the metabolic differences induced by food processing are linked to differences in the brain's response to food stimuli.
The study's findings suggest that food processing can influence the way the body and brain respond to food in ways that go beyond nutritional composition and calories: this could potentially help researchers understand why ultra-processed foods have been linked to overeating and negative long-term health outcomes. Today, ultra-processed foods account for more than half of the average American's daily calories and a quarter of an Italian's. An increasing number of populations are incorporating them into their diets: these products are formulated to be convenient, accessible, affordable and palatable, to the point of driving overconsumption.
"People who consume large quantities of ultra-processed foods show higher rates of health problems, such as obesity, cardiac events, type 2 diabetes and even some markers of mental health," explained Alex DiFeliceantonio, one of the study's authors.
The researchers now wish to build on these findings with studies involving different populations, longer time frames, larger meals and a greater number of combinations between minimally processed and ultra-processed foods. Although the meals administered were equivalent in terms of protein content, the protein sources differed and may have influenced the results. The ultra-processed meal also contained a greater quantity of additives and, while the study measured total fibre content, it did not explicitly analyse the physical and chemical characteristics of the foods examined.