Scientists dispute ultra-processed food definition and research on health impact

04 Jul 2024 --- The impact of ultra-processed foods (UPFs) on health and disease risk is extensively studied, with researchers presenting the latest findings at the recent International Congress on Obesity (ICO 2024) and the annual meeting of the American Society for Nutrition (Nutrition 2024). While one study found that UPF consumption increased the risk of death, another suggests that limiting UPFs “does not necessarily make for a healthy diet.” This leads experts to debate the validity of processing levels to determine a food’s healthiness.

At ICO 2024, professor Carlos Monteiro of the University of São Paulo, Brazil, argued that UPFs are pushing aside other food groups. The creator of the NOVA classification system, which categorizes foods into four groups according to their processing level, recommended that UPFs be regulated in a similar way as tobacco, with warning labels and advertising restrictions. 

“Treating food like tobacco is very simplistic,” counters Dr. Hilda Mulrooney, a reader in nutrition and health at London Metropolitan University, UK. “There is no such thing as a safe cigarette, even second-hand, so banning them is relatively straightforward in that the health case is obvious.” 

“However, we need a range of nutrients, including fat, sugar and salt, and they have multiple functions in foods — structural, shelf life — not just taste and flavor and hedonic properties.  It is not as easy to reformulate some classes of foods to reduce them, and they are not the same as tobacco because we need food — just not in the quantities most of us consume.” 

She concedes that healthcare professionals and dietitians advocate for taxes on less healthy foods. However, she adds that this does not focus only on UPFs as per the NOVA classification but on their nutritional content. Mulrooney notes that NOVA does not consider this nutritional content — “a reason many people have problems with this classification system.” 

Healthy minimal processing? 
A study presented at Nutrition 2024 found that a less processed food menu was more than twice as expensive as a UPF-focused menu and reached its expiration date over three times faster without delivering any additional nutritional value. 

The researchers compared two menus reflecting a typical Western diet, one deriving 20% of calories from UPFs and another obtaining 67% of calories from UPFs. Both menus had a relatively low Healthy Eating Index score of around 43–44 out of 100, reflecting poor adherence to the Dietary Guidelines for Americans. 

Research finds that menus with higher UPF content were cheaper and had a longer shelf life.“This study indicates that it is possible to eat a low-quality diet even when choosing mostly minimally processed foods,” says Dr. Julie Hess, a research nutritionist at the USDA-ARS Grand Forks Human Nutrition Research Center and lead author of the study. 

“It also shows that more-processed and less-processed diets can be equally nutritious (or non-nutritious), but the more-processed diet may have a longer shelf life and be less costly.”

The researchers estimated the less processed menu at a daily cost of US$34.87 and the more processed menu at US$13.53 per day. The median expiration time of the less processed menu items was calculated at 35 days, compared to 120 days for the more processed menu. 

Hess highlights that several nutrient-dense packaged foods, such as unsweetened applesauce, ultra-filtered milk, liquid egg whites and some raisins or canned tomatoes, can be classified as UPFs. 

“The concepts of ‘ultra-processed’ foods and ‘less-processed’ foods need to be better characterized by the nutrition research community,” she argues. 

Risk of death 
Meanwhile, another study presented at Nutrition 2024 finds that older adults with higher consumption of UPFs were around 10% more likely to die than people consuming less processed foods over an average 23-year follow-up period. 

The research used data from over 540,000 people, providing information on their eating habits and health in the mid-1990s. 

“We observed that highly processed meat and soft drinks were a couple of the subgroups of UPFs most strongly associated with mortality risk, and eating a diet low in these foods is already recommended for disease prevention and health promotion,” comments Erikka Loftfield, Ph.D., Stadtman investigator at the National Cancer Institute. 

Moreover, people in the 90th percentile for UPF consumption tended to have a higher body mass index and a lower Healthy Eating Index score. However, after controlling for diet quality and weight, the associations between higher UPF intake and mortality risk persisted. 

At the same time, Lotfield cautioned that the study design did not allow the researchers to determine causality. Also, people’s diets may have changed considerably since the study’s baseline 30 years ago. 

Experts argue that the nutritional content is a better classification for healthy foods than processing level.NOVA classification limitations 
Dr. Duane Mellor, dietitian and spokesperson for the British Dietetic Association, argues that the NOVA classifications are “open to subjective interpretation.” For example, he illustrates that the system does not consider beer or wine as UPFs but includes traditional foods such as tofu and tempeh as ultra-processed. 

“This doesn’t take into account other research which highlights the potential of these soya-based foods to reduce cholesterol, for example, and may understate the risks of alcohol consumption.” 

He argues: “If a classification of UPF is to be used, it would need to be objective and possibly have a locally appropriate approach to suit the food systems and supply in other countries.” 

Mellor highlights that not all research uses the same UPF definition. For example, a recent study excluded ultra-processed wholegrain cereals from a diet. He calls for a globally agreed-upon objective definition that can be applied without needing to make judgments about food so that foods can be “reliably classified” according to their processing level and healthiness. 

Processing vs. nutrient profile  
Gunter Kuhnle, professor of Nutrition and Food Science at the University of Reading, UK, adds that there is “no evidence” for the claim that ultra-processing creates a worse nutrient profile than simple processing. 

Some UPFs high in sugar, fat or salt are known to harm health. However, others can be an essential source of fiber, wholegrain or fish. 

“Ultra-processed bread — most bread consumed in the UK — often has higher amounts of wholegrain and fiber than comparable non-ultra-processed breads,” illustrates Kuhnle. “Moreover, ultra-processing allows a reduction in salt intake and many supermarket breads meet the recommendations for salt reduction (in contrast to many artisan breads).” 

“In my view, there is a high risk that if we focus on the level of processing, this could distract from the evidenced problems that make it more difficult to find solutions to address diet-related health problems.” 

By Jolanda van Hal