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Researchers Dispute Findings of Study on the Appeal of Ultra-Processed Foods

Three burgers.
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Ultra-processed foods, such as crisps/chips, are no more “appealing” than less processed foods, such as apples and eggs – that’s according to a new study published in Appetite by researchers at the University of Bristol.

These surprising findings have been called into question, however, by certain food and nutrition researchers. Their main critique: the study’s participants judged pictures of food, not actual food.

More than meats the eye

The study’s authors, from the University of Bristol’s Nutrition and Behaviour Group, set out to test the common but largely untested assumptions that a food’s level of processing influences its desirability.

The research involved 224 adult volunteers who were asked to rate food for qualities such as “taste pleasantness”, “desire to eat”, sweetness and saltiness. 

Due to the COVID-19-related social distancing restrictions at the time, participants took part in the study virtually and were asked to judge photographs of the foods based on “imagined consumption.”

These 52 food images included avocados, grapes, cashew nuts, king prawns, olives, a blueberry muffin, crispbread and ice cream.

The University of Bristol researchers found that, on average, ultra-processed foods were no more liked or desired by the participants than processed or unprocessed foods.

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

Rogers and his colleagues also observed that the participants seemed to favor foods with equal calorie amounts of fat and carbohydrates.

“Our suggestion is that humans are programmed 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,” noted Rogers.

Other researchers, however, aren’t as wowed by the study’s findings.

The food critics

“Although this study showed that images of ultra-processed foods 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,” Dr. Duane Mellor, a registered dietitian and senior lecturer at Aston University, said in a reactive statement issued by the UK’s Science Media Centre.

“Therefore, any claims that this study is able to ‘challenge the assumption that ultra-processed foods are hyperpalatable as stated by [the] study’s lead author, is very hard to justify.”

“Simply seeing a food is only one part of how much food will be chosen and then eaten,” Mellor continued, “as other factors such as its flavor, sensation and the biological changes in our bodies (such as hormonal and glucose changes) which result from the act of eating a food, all combine to influence how palatable and how much food is ultimately consumed.”

“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,” Mellor added.

His comments were echoed by Thomas Sanders, a professor of nutrition and dietetics at King's College London.

“The study failed to demonstrate any evidence to suggest that ultra-processed foods were perceived as more palatable by adults,” Sanders said in a statement to the Science Media Centre.

“Food choice in the real world is influenced by packaging, placement of the product at point of sale, as well smell, taste and social context. Furthermore, the findings of this study cannot be generalized to children.”

Technology Networks reached out to Professor Rogers for a response to these critiques. He gave the following statement.

“Although this was a virtual study, as we say in our paper, we have direct evidence that the responses of participants to the foods were valid. First, the participants’ ratings of the sweetness and saltiness of the foods were related, as expected, to the sugar and salt content. These relationships were of the same magnitude as found in studies in which foods were tasted – with some of those studies having expert sensory-panelists rating the foods. Second, we found that how hungry the participants were affected their desire to eat the food, but not their liking rating (taste pleasantness), which replicates findings from lab studies of tasting and eating foods. And third, our study replicated and extended previous research demonstrating a relationship between carbohydrate-to-fat ratio and food reward. Furthermore, it is self-evident that when we (humans) are familiar with a food, we find it easy to imagine how it will taste and how nice it will be to eat it – indeed that substantially influences our likelihood of buying and eating it.”

“Essentially, our study showed that liking (taste pleasantness) and food reward (desirability) was predicted by carbohydrate-to-fat ratio, fiber content (negatively), and taste intensity (mainly sweetness and saltiness), but not by being ultra-processed. Hence our conclusion that the claim that ultra-processed foods are 'hyper-palatable' is not supported. This claim is based on supposition – our study collected data that tested the claim.”

Reference: Rogers PJ, Vural Y, Berridge-Burley N, Butcher C, Cawley E, Gao Z, Sutcliffe A, Tinker L, Zeng X, Flynn AN, Brunstrom JM. Evidence that carbohydrate-to-fat ratio and taste, but not energy density or NOVA level of processing, are determinants of food liking and food reward. Appet. 2023. doi: 10.1016/j.appet.2023.107124

Professor Peter Rogers was speaking to Leo Bear-McGuinness, science writer for Technology Networks.