An ongoing study in the press with the journal Contemporary clinical trialsResearchers examine how consuming ultra-processed foods (UPF) affects physiological processes related to energy intake (EI) and reward processing.
Overweight and obesity are on the rise worldwide, leading to various health problems such as heart disease. Scientists have found that even young adults (ages 18 to 30) who are at the medically recommended weight have a high risk of becoming overweight or obese over the next quarter century.
Poor eating habits are well documented among adolescents and young adults in the United States. More than two-thirds of their EI is thought to come from UPF, with little to no whole food. Scientists worry that these foods may change how people make food-related decisions and lead to overweight and obesity.
Study: Effects of ultra-processed food intake on reward processing and energy intake: background, design and methods of a controlled feeding trial in adolescents and young adults.. Image credit: Celso Pupo/Shutterstock
UPF foods have high rewards but little nutrition
Studies in humans and mice have shown how processed foods can affect the brain’s dopamine system. Rats fed bacon and snow quickly gained weight, which was thought to be related to lower function of D2 dopamine receptors (D2R) in the striatum, a brain region associated with food intake and reward modulation.
Animals fed a high-sugar diet and humans exposed to a high-fat, high-sugar diet show similar effects. People with higher body mass index (BMI) have reduced D2R function points to UPF’s role in increasing EI, which can lead to overweight and obesity.
However, only one trial has examined this relationship in adult humans, and no studies have focused on how UPF consumption in early adulthood can alter brain chemistry and how people perceive rewards from food.
These changes, occurring during the critical transition between childhood and adulthood, have implications throughout one’s life as cognitive processes such as inhibitory control mature at this age. Thus, UPF may alter executive function (EF) related to inhibitory control, working memory, and cognitive flexibility, leading people to eat more when they are not hungry.
Exploring how UPF affects EF in young adults
The ongoing clinical trial will recruit participants between the ages of 18 and 25 who are either sedentary or recreationally active. Individuals with food allergies will not be included. During the recruitment process, physical and dietary recall data will be assessed. Participants will also be screened with a mock functional magnetic resonance imaging (fMRI) scan to ensure they are not claustrophobic.
At baseline, researchers will collect data on body weight and composition, conduct an fMRI, and ask participants to complete a delay discounting task and cognitive EF tasks. They estimated that they would need 32 participants at the start of the study to account for attrition and to ensure that they had at least 26 participants and sufficient statistical power for causal inference.
All participants will then be exposed to the two diets for two weeks. On one diet, participants would get 81% of their EI from UPF, while the other diet would have no UPF. These diets will be designed to be similar in terms of overall quality, nutrition, texture and palatability and will be formulated for weight maintenance. They will contain 15% protein, 35% fat and 50% carbohydrates.
Participants will eat their breakfast at the laboratory Monday through Saturday and will be provided with meals for the rest of the day. Meals for Sunday will be provided in advance. Any leftover food will be returned to the laboratory, and cost, deviation and compliance data will be recorded.
In addition to food, participants will be given a choice of snacks and buffet meals to assess their preference between UPF and non-UPF food. There will be a four-week “washout period” between the two controlled feeding periods. After each feeding period, another fMRI will be taken, and physical measurements and cognitive function will be monitored. For each of the four diet days, participants will wear an accelerometer to measure physical activity.
Researchers will study the mechanisms by which UPF modulates reward processing. They will explore the body’s blood oxygenation level-dependent (BOLD) response, as well as EI between meals, using statistical methods such as analysis of variance (ANOVA) with mixed effects and general linear mixed models.
They hypothesized that UPF foods would weaken the BOLD response in the ventromedial prefrontal cortex and striatum, which are brain reward centers. They expect that the UPF diet will increase preference for UPF food items, as well as EI, in foods. Finally, they theorized that UPF diets would reduce EF performance by impairing immune regulation.
Implications of the study
Although emerging research highlights the adverse health effects of UPF, commercial consumption remains widely popular. Researchers believe that these foods are addictive and that they weaken our natural ability to control EI. Understanding how these foods alter decision-making ability and brain chemistry is key to formulating more effective public health guidelines and regulations for commercial food companies to promote healthy diets.
- Effects of ultra-processed food consumption on reward processing and energy intake: background, design and methods of a controlled feeding trial in adolescents and young adults. Rego, MLM, Leslie, E., Capra, BT, Helder, M., Yu, W., Katz, B., Davy, KP, Hedrick, VE, Davy, BM, DiFeliceantonio, AG. Contemporary clinical trials (2023). https://doi.org/10.1016/j.cct.2023.107381, https://www.sciencedirect.com/science/article/pii/S155171442300304X?via%3Dihub