Study finds ultra-processed foods no more palatable than (un)processed but experts dispute results

27 Nov 2023 --- Based on an online study, UK researchers suggest ultra-processed foods (UPFs) are no more desired than processed or unprocessed foods, as previously assumed. Instead, they argue that carbohydrate-to-fat ratio and taste primarily determine whether people like a food, not their level of processing or energy density.

Foods that scored higher on liking (palatability) and desire to eat include those that combine equal amounts (in calories) of carbohydrate and fat — known as the “combo” effect in previous research — and those with an intense taste. Participants liked foods containing a lower fiber content. 

“Our results challenge the assumption that ultra-processed foods are ‘hyper-palatable,’ and it seems odd that this has not been directly tested before,” says the study’s lead author, Peter Rogers, professor in the School of Psychological Science at the University of Bristol, UK. 

“However, while ultra-processing didn’t reliably predict liking in our study, food carbohydrate-to-fat ratio, food fiber content and taste intensity did — together, these three characteristics accounted for more than half of the variability in liking across the foods we tested.”

The researchers note that the study’s outcomes support the theory that humans are programed to learn to like foods with equal amounts of carbohydrates and fat. 

Meanwhile, Dr. Duane Mellor, registered dietitian and senior lecturer at Aston University, UK, cautions that the study cannot assess the suggestion that UPFs are preferred to less processed foods, as the participants did not eat these foods. 

“It is important that we do not use research based on looking at pictures of food to assess how tasty, palatable, or ultimately, its effect on our health.”

In the online study, volunteers viewed color images of familiar foods and scored how much they liked and desired these.Study set up 
The study, led by the University of Bristol’s Nutrition and Behaviour Group, aimed to test the common assumptions that food energy density (calories per gram), level of processing and carbohydrate-to-fat ratio primarily influence food liking and desirability. 

While the researchers planned to conduct a laboratory-based study, COVID-19 restrictions in the UK prevented face-to-face testing. The results are published in Appetite. 

Instead, the team reverted to an online study, where 224 volunteers viewed color images of familiar foods. Participants were randomized into one of three groups, focusing on energy-dense foods (32 foods), level of processing (24 foods) or carbohydrate-to-fat ratio (24 foods).

Based on the pictures, the participants rated the foods for taste pleasantness (liking), desire to eat (food reward) and sweetness, saltiness and flavor intensity (taste intensity). The researchers explain that the validity of this method was confirmed by a strong relationship between sweetness ratings and food-sugar content, as well as a correlation between saltiness ratings and food-salt content. 

The authors note that the study method relates to how consumers judge familiar foods when anticipating eating. 

The study included 52 foods, including avocado, grapes, cashew nuts, king prawns, olives, blueberry muffins, crispbread, pepperoni sausages and ice cream.

Consumer preferences 
Participants liked foods with higher dietary fiber content less, while those with a more intense sweet or salty flavor were more liked and desired. 

“The results for sweetness and saltiness are consistent with our innate liking for sweetness and saltiness. And the results for carbohydrate-to-fat ratio and fiber might be related to another important characteristic that determines food liking,” explains Rogers. 

“We suggest that humans are programed to learn to like foods with more equal amounts of carbohydrate and fat and lower amounts of fiber because those foods are less filling per calorie. In other words, we value calories over fullness.”

He adds that this preference helps humans maximize calorie intake and build up fat reserves when food is abundant. “This is adaptive when food supplies are uncertain or fluctuate seasonally, but not when food is continuously available more than our immediate needs.”

The research group also tests the idea of calories versus fullness in additional studies on food liking and meal preferences across countries and cuisines. 

Mellor argues there is no direct link between liking or desiring a food in a picture and finding it highly palatable when eating it.Challenging outcomes  
Meanwhile, Mellor asserts that any claims that the study can “challenge the assumption that ultra-processed foods are ‘hyper-palatable’” are hard to justify. 

“Although this study showed that images of UPFs were not more desirable than less processed foods, this did not look at how much of these foods would have been eaten by the participants had they been given the opportunity.” 

For example, he shares that a previous study in the US showed that UPFs matched nutrients to less processed foods, resulting in greater consumption and calorie intake. 

“There is no direct link between liking or desiring a food in a picture and finding it highly palatable when eating it. This is because simply seeing food is only one part of how much food will be chosen and eaten,” underscores Mellor. 

“Other factors such as its flavor, sensation and the biological changes in our bodies (such as hormonal and glucose changes), which result from eating a food, all influence how palatable and how much food is ultimately consumed.” 

Ultra-processed foods 
Earlier this month, researchers in a WHO-backed study linked UPF consumption with a higher risk of chronic diseases, though not all food categories had the same association. Ultra-processed breads and cereals, as well as plant-based alternatives, lowered disease risk. 

Meanwhile, scientists proposed classifying UPFs rich in carbohydrates and fats as addictive substances. They found that around 14% of adults and 12% of children could be addicted to UPFs, which is a similar rate to addiction to tobacco and alcohol. 

At the same time, the plant cell tech company Ayano Bio highlighted that many US consumers are open to incorporating UPFs in their diets and would pay more for these options, emphasizing that taste, ingredient quality and convenience are the most critical drivers for this consumption. 

By Jolanda van Hal