A tightly controlled feeding trial shows that teenagers eat more after two weeks on an ultraprocessed diet, even when meals are matched for calories and nutrients, suggesting that adolescence may be a critical window of vulnerability to modern food environments.
Study: The Influence of Ultraprocessed Food Consumption on Energy Intake in Emerging Adulthood: A Controlled Feeding Trial. Image credit: EugeneEdge/Shutterstock.com
Young individuals in late adolescence appear to be more susceptible to increased energy intake (EI) following a diet with increased ultra-processed foods (UPF). A recent study in Obesity compared EI among young individuals who consumed a diet high in UPF with those who consumed more non-UPF in a controlled, short-term feeding trial.
Rapid surge in obesity among adolescents
According to a recent study, one in three Americans between 15 and 24 years of age is at a higher risk of becoming obese by 2050. Overweight adolescents are highly likely to reach adulthood with obesity, making them susceptible to cardiovascular diseases. In addition, this population may develop many comorbidities, such as diabetes and depression, which affect their quality of life.
Researchers have identified many factors that contribute to obesity among adolescents. Poor dietary choices could be one of the main contributing factors to weight-related issues. Individuals who indulge in excessive EI, high UPF consumption, and consume food with poor nutritional content are at a higher risk of obesity.
What are processed foods?
The Nova classification system categorizes foods by processing level and purpose into unprocessed and minimally processed foods (group 1), processed culinary ingredients (group 2), processed foods (group 3), and UPF (group 4). Unprocessed foods include fresh produce, while processed culinary ingredients are those products used for seasoning (e.g., oil and sugar).
Processed foods are manufactured by combining groups 1 and 2 products to increase durability, while UPFs undergo industrial manufacturing techniques and combine substances that are commonly not used in home cooking.
Higher UPF consumption is often attributed to their wide availability, low cost, and appealing taste. Previous research suggests that UPFs account for approximately 55 % to 65 % of total energy intake among U.S. children and young adults.
In adults, high UPF intake has been linked to a greater risk of type 2 diabetes, cardiovascular disease, depression, and obesity. However, relatively few studies have investigated the relationship between UPF consumption and adiposity, as well as the risk of overweight or obesity in adolescents. Understanding the causal relationships between UPF exposure, excess energy intake, and weight gain remains an important research priority.
Controlling diets across ages
A partial-domiciled, crossover feeding trial was designed to evaluate the effects of UPF consumption on ad libitum EI in individuals aged 18 to 25. The current study hypothesized that the UPF diet would lead to a greater ad libitum EI compared to the non-UPF diet.
Participants underwent two 14-day controlled feeding periods in a randomly assigned order. A 4-week washout period was maintained between conditions. A block-randomized approach was used, with age, sex, and body mass index (BMI) status as randomization factors.
Participants were introduced to one of two eucaloric diets: a high-UPF diet (81% of calories from UPF) or a non-UPF diet (0% of calories from UPF). Each participant was offered an ad libitum buffet meal, and their EI, food selection, and meal intake rate were recorded. Their weight and body composition were measured before and after each diet condition.
Daily menus included three meals and a snack and were designed for each condition at four energy levels: 1,500 kcal, 2,000 kcal, 2,500 kcal, and 3,000 kcal. As exploratory analyses, eating in the absence of hunger (EAH) was estimated after each condition. Baseline executive functions (EF), which are cognitive processes for self-regulation and decision-making that mature throughout adolescence and into young adulthood, were also examined as possible predictors of UPF consumption during ad libitum meals.
Eating pattern changes
A total of 33 participants were randomized to one of two diet conditions, with an 85 % retention rate. Participants lost weight on both diets, i.e., 416 grams on the UPF diet and 477 grams on the non-UPF diet. This weight change was within the range of normal daily fluctuations in body weight.
Participants under the UPF diet experienced a 0.68 % reduction in body fat, while those under the non-UPF diet showed a stable body fat. Dietary compliance for the UPF and non-UPF conditions was 99.1 % and 98.9 %, respectively. Physical activity did not differ between conditions. Urinary excretion of sodium, potassium, and nitrogen strongly correlated with the nutrient content of the menu for both conditions.
No significant effect was observed in the full sample for total kcal consumed, UPF and non-UPF grams consumed, or for eating rate. Furthermore, no differences were observed in food item selection and fasting Visual Analog Scale (VAS) ratings of fullness, hunger, or thirst.
The researchers found an interaction between diet condition and age: adolescents consumed more total calories after the UPF diet, whereas young adults showed a small, non-significant decrease. Importantly, VAS ratings indicated that adolescents were not hungrier than young adults across either diet condition, suggesting that differences in appetite did not explain the increased intake.
In the EAH task, adolescents consumed more non-UPF calories after the UPF diet than after the non-UPF diet, largely due to greater intake of a non-UPF potato chip option. This pattern was not observed in the young adult group, who showed no meaningful difference in their food choices between diet conditions.
Adolescents also consumed more total EAH kcal after the UPF diet. No interactions were found between EF baseline measures and diet conditions for EAH outcomes.
Teens show heightened UPF sensitivity
Adolescents consumed more calories after the UPF diet than after the non-UPF diet; however, these age-related differences were exploratory and based on a small subgroup, so additional studies are needed to confirm them.
Future research should extend dietary interventions beyond 14 days and include larger, more diverse samples. It may also be valuable to incorporate measures such as sleep patterns, appetite-regulating hormones, and chronotypes.
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