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 the 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. There were 52 different foods in total, including avocado, grapes, cashew nuts, king prawns, olives, blueberry muffin, crispbread, pepperoni sausage, and ice cream.
Participants were then asked to rate the foods for taste pleasantness (liking), desire to eat, sweetness, and saltiness while imagining tasting them. 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 mostly as fat. This is known, from previous research, as the ‘combo’ effect.
Further results revealed that foods with higher amounts of dietary fibre were less liked and desired, and foods tasting more intense (mainly related to the level of sweetness and saltiness), were more liked and desired.