Are ultra-processed foods preferred to less processed foods?

Research that compared the taste perception of less processed foods with ultra-processed foods (UPFs) found participants viewed UPFs no more pleasant tasting than less processed foods. The study, led by Bristol’s Nutrition and Behaviour Group, wanted to test the common but largely untested assumptions that food energy density (calories per gram), level of processing and carbohydrate-to-fat ratio are key factors influencing food liking and desirability.

In an experiment involving 224 adult volunteers, participants were presented with colour images of between 24 and 32 familiar foods, varying in energy density, level of processing (including UPFs) and carbohydrate-to-fat ratio. In total, there were 52 different foods, including avocado, grapes, cashew, nuts, king prawns, olives, blueberry muffin, crispbread, pepperoni sausage and ice cream.

Participants were asked to imagine tasting the foods and rate them for taste pleasantness, desire to eat, sweetness and saltiness. The validity of this method was confirmed by, for example, finding a strong relationship between sweetness ratings and food sugar content.

Results from the study showed that, on average, UPFs were no more liked or desired than processed or unprocessed foods. However, foods that combined more equal amounts (in calories) of carbohydrate and fat were more liked and desired than foods containing the same number of calories mostly as carbohydrate or fat. In previous research, this has been known as the ‘combo’ effect.

Results also revealed that foods with higher amounts of dietary fibre were less liked and desired while foods tasting more intense, relating mainly to the level of sweetness and saltiness, were more liked and desired.

Professor Peter Rogers in the School of Psychological Science, lead author of the study, said the results for UPFs were surprising as they challenge the assumption that ultra-processed foods are hyperpalatable.

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

“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 fibre might be related to another important characteristic that determines food liking,” Rogers said.

The researchers suggested that humans value calories over fullness and are programmed to learn to like foods with more equal amounts of carbohydrate and fat and lower amount of fibre, because they are less filling per calorie.

“In turn, this trait helps us to maximise calorie intake and build up fat reserves when food is abundant — which is adaptive in circumstances when food supplies are uncertain or fluctuate seasonally, but not when food is continuously available in excess of our immediate needs,” Rogers said.

The Nutrition and Behaviour Group is currently undertaking further food liking and meal preference studies on the calories versus fullness idea, testing across different countries and cuisines.

This research was funded by the University of Bristol’s School of Psychological Science.

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