For thousands of years, humans have modified food to suit their tastes and improve nutrition. The process of nixtamalisation, which dates back over 3,000 years in Mesoamerica, allowed the extraction of nutrients from corn by cooking it in a solution of wood ash or lime, making it more digestible. Fast-forward to the 19th century, and industrial processes such as tinned goods and pasteurisation revolutionised food production, making food cheaper, more accessible, and convenient.
The global food supply has risen by more than 20% in the last 60 years, while obesity rates have surged dramatically. Today, nearly one-third of the world’s population is overweight or obese, highlighting the growing concern over dietary patterns.
However, as we consider the causes of rising obesity rates, ultra-processed foods (UPFs) have come under increasing scrutiny. UPFs, a term coined by Brazilian scientist Carlos Monteiro, refer to foods that undergo significant processing, resulting in products that are often nutrient-poor but highly appealing in terms of taste and convenience. While concerns about the impact of UPFs have been growing, new research is attempting to pinpoint why these foods may be contributing to public health issues, such as obesity, type-2 diabetes, cardiovascular diseases, and mental health disorders.
The Rise of Ultra-Processed Foods
The classification of foods into categories based on their level of processing is a relatively new concept. Monteiro’s “Nova” system divides foods into four groups:
- Group 1: Minimally processed foods (e.g. fruit and vegetables).
- Group 2: Processed culinary ingredients (e.g. butter, salt).
- Group 3: Processed foods (e.g. tinned vegetables, bread, cheese).
- Group 4: Ultra-processed foods, which include fizzy drinks, sugary cereals, frozen pizzas, and ready-to-eat snacks. These foods contain artificial additives such as hydrogenated oils, high-fructose corn syrup, and emulsifiers.
Over the past few decades, the global consumption of UPFs has exploded. In countries like the US and the UK, UPFs now account for over half of total calorie intake. While these foods are often high in fat, sugar, and salt—nutritional factors known to contribute to poor health—recent studies suggest that the processing itself may play a significant role in the health risks associated with UPFs.
The Link Between UPFs and Poor Health
Research has increasingly pointed to a direct link between UPFs and poor health, independent of their nutritional content. A 2023 study by Samuel Dicken and Rachel Batterham from University College London reviewed 37 studies and found that even after adjusting for the levels of sugar, fat, and salt, UPFs remained strongly linked to a variety of health issues. This raises the question: Are UPFs unhealthy because of their nutrient profile, or is the very act of processing a factor in their harmful effects?
One landmark study, led by Kevin Hall at the National Institutes of Health (NIH), explored the effects of UPFs by tracking the food intake of 20 adults for four weeks. The participants were given either ultra-processed or minimally processed foods in two-week intervals, while their calorie intake and nutrient consumption were controlled.
The results were striking. Participants on the ultra-processed diet consumed around 500 more calories per day than those on the minimally processed diet, leading to an average weight gain of 1kg (2.2 pounds) in two weeks. By contrast, those on the minimally processed diet lost a similar amount of weight. This suggests that factors other than just the higher content of fats, sugar, and salt in UPFs may be influencing overeating and weight gain.
Hall’s work is part of a growing body of evidence suggesting that UPFs are more energy-dense than minimally processed foods, contributing to overeating. These foods often pack more calories into smaller portions, and the brain may not register fullness as effectively. Additionally, UPFs are frequently engineered to be “hyper-palatable”—exceedingly tasty combinations of fats, sugars, and salt—that encourage overeating.
The Growing Concern: Can ‘Healthy’ UPFs Still Contribute to Obesity?
While much of the research has focused on ‘junk foods’, a new question has emerged: Do these problematic characteristics also apply to ‘healthier’ UPFs? Some ultra-processed products, such as certain breakfast cereals, yoghurt, or bread, may be marketed as healthier alternatives but still undergo extensive industrial processing.
A recent study, looking at a range of UPFs across different categories, found that many ‘healthy’ ultra-processed foods still share troubling characteristics. These products may not trigger the typical warning labels for high sugar, fat, and salt, yet they tend to have higher energy densities than minimally processed options. Even in the absence of obvious ‘red light’ labels, their higher energy density and hyper-palatable characteristics still pose a risk for overconsumption and subsequent weight gain.
Interestingly, some ‘healthier’ ultra-processed foods exhibited a similar nutritional profile to minimally processed options in terms of fat, sugar, and salt levels, but were still found to be more energy-dense and more likely to trigger overeating due to their palatability. These findings suggest that the degree of processing itself—not just the specific ingredients—may play a significant role in the risk of overconsumption and obesity.
The Role of Energy Density and Hyper-Palatability
Energy density and hyper-palatility are key factors that help explain why UPFs contribute to overeating. Energy-dense foods are those that provide more calories in smaller volumes, which leads to greater calorie consumption without feeling full. Hyper-palatable foods, which are designed to be irresistible, prompt more frequent and faster eating, bypassing the body’s natural signals of fullness.
Research by Kevin Hall is set to provide more clarity on the specific mechanisms behind overeating linked to UPFs. His latest study, examining the effects of energy density and palatability in more detail, will shed light on the importance of these factors in driving overconsumption.
Conclusion
The research into ultra-processed foods continues to evolve, and it is clear that these foods—whether labelled ‘healthy’ or not—tend to share common characteristics that encourage overeating. Their higher energy density and greater palatability may be key drivers of the rising obesity epidemic.
As the research landscape develops, policymakers will need to consider the broader implications of food processing, beyond just the nutrient composition. Greater understanding of the dynamics of energy density and palatability will be essential in developing more accurate guidelines and policies to protect public health.
While the focus on UPFs is not new, this growing body of research highlights the need for clearer definitions and better strategies to tackle the harmful effects of these foods, whether or not they are marketed as ‘healthy’. The findings could ultimately help shape healthier food environments and better public health initiatives.
Read More:
- Scientists are learning why ultra-processed foods are bad for you. Economist article (25th November 2024)
- Dicken S, Makaronidis J, van Tulleken C, et al UPDATE trial: investigating the effects of ultra-processed versus minimally processed diets following UK dietary guidance on health outcomes: a protocol for an 8-week community-based cross-over randomised controlled trial in people with overweight or obesity, followed by a 6-month behavioural intervention. BMJ Open 2024;14:e079027. doi: 10.1136/bmjopen-2023-079027
https://bmjopen.bmj.com/content/14/3/e079027.long
- Fazzino TL, Courville AB, Guo J, Hall KD. Ad libitum meal energy intake is positively influenced by energy density, eating rate and hyper-palatable food across four dietary patterns. Nat Food. 2023 Feb;4(2):144-147. doi: 10.1038/s43016-022-00688-4. Epub 2023 Jan 30. PMID: 37117850.
https://www.nature.com/articles/s43016-022-00688-4
- Effect of Ultra-processed Versus Unprocessed Diets on Energy Metabolism- New Research
