Background
Research has highlighted the global spread of Western dietary patterns, particularly the increased consumption of ultra-processed foods (UPFs) across different economic stages. While UPFs are often high in saturated fats, salt, and sugar, their classification has become more complex due to evolving formulations. Despite ongoing debates about the classification and health impact of UPFs, their significance in global food systems cannot be ignored. According to some estimates, UPFs contribute over 50% of the population’s caloric intake in the United States, while consumption of health-beneficial foods has decreased. Many people may face challenges accessing and affording healthier alternatives, leading to poorer health practices.
However, current UPFs can contribute to raising scores according to the Healthy Eating Index (HEI) despite lacking essential nutrients. Epidemiological evidence links UPF consumption to current health conditions like obesity, diabetes and cardiovascular disease. Debates surround whether UPFs’ adverse health effects stem from their nutrient-poor content or additives that imitate natural flavors, leading to discussions on banning UPFs or reformulating them for better health outcomes. The narrative review aims to advance understanding by examining systems for food classification and proposing guidelines for UPF formulation and consumer selection.
Systems for food classification
Food classification systems aim to categorize foods based on shared characteristics, typically for providing dietary guidance and informing nutrition policies. Traditional systems, like the US Dietary Guidelines, focus on culinary definitions and nutritional needs. However, concern over the health impacts of food processing has led to alternative classification schemes. These newer systems, such as NOVA, categorize foods based on the extent and purpose of processing, distinguishing between minimally processed, extracted substances and UPFs. While the NOVA system is widely used, it has faced criticism, prompting research into alternative classification methods. Recent advancements include machine learning algorithms, like FoodProX, which assess the degree of food processing and link dietary quality to NCD risk biomarkers.
Causal evidence regarding UPFs
Studies indicate a lack of clear causal evidence linking UPFs directly to adverse health outcomes. The researchers identified four categories for further investigation: energy balance, nutrient density, food processing, and use of non-culinary additives. The current evidence suggests a positive association between UPF intake and obesity risk, even when controlling for calorie intake, suggesting that energy balance alone may not explain the association between UPFs and health issues. While early assumptions linked UPFs with poor nutritional content, many nutrient-dense UPFs are now available. Poor nutritional status could be a biomarker for other processes that modify non-communicable disease risk, but whether these products affect their likelihood is unclear.
Specific food processing techniques and additives have been implicated in a higher risk of these conditions. These alterations may affect the gut microbiome and contribute to metabolic diseases. It is crucial to investigate the effects of refined macronutrients, additives, microbial products, and novel chemicals formed during processing. A decision tree framework can be used to explore causality by implementing a series of experiments to determine whether factors related to UPFs affect the risk for diabetes, obesity, hypertension and cardiovascular diseases. Preclinical models, such as mouse models of hepatic steatosis, can be used to investigate these factors systematically.
The associated risk for kidney disease
Chronic kidney disease (CKD; all stages) affects averagely 12% of the global population, with its prevalence within the United States estimated to be about 15% among adults. Epidemiological studies have reported associations between the consumption of certain foods, nutrients, and dietary patterns and the risk of CKD; however, less is known about the impact of food processing on the incidence of CKD. Beside the likely association with diabetes, metabolic disease and even some kind of cancers, previous reports suggest significant associations between high UPFs consumption. A last review including 8 valid studies comprising 500.000 people, found that the highest UPFs intake category was associated with an 18% increased risk of CKD compared to the lowest category. Moderate heterogeneity was observed in the reviewed studies, thus necessitating the use of a fixed-effects model. A subgroup analysis involving cohort studies reproduced the positive association between UPFs intake and CKD risk, with less heterogeneity.
Reformulating UPFs for health benefits
Developers of the NOVA system recommend limiting UPF intake. Several strategies have been identified to promote healthier eating habits and counteract the dominance of UPFs in the food system, such as promoting the preparation of healthy food, increasing support for family farmers, and creating public health policies to regulate UPFs with low nutritional value. However, these recommendations overlook the appeal of UPFs to consumers, including their palatability and convenience. Limiting UPF availability and consumption could reduce food security, especially among vulnerable populations like older adults. An alternative approach is reformulating UPFs to make them healthier. Whole-food formulation, which replaces processed ingredients with intact or minimally processed ones, is one such approach. Changing agricultural and economic incentives could encourage the development of healthier processed foods.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Scientific references
Xiao B et al. Ren Fail. 2024 Dec; 46(1):2306224.
de Farias VF et al. BMC Pub Health. 2024; 24(1):982.
Shateri Z et al. BMC Nephrol. 2024 Jan; 25(1):4.
Avesani CM et al. Clin Kidney J. 2023; 16(11):1723.