Prevention of chronic diseases has therefore been considered a public health challenge in the past decades 2. Besides physical activity, the nutritional quality of the diet is a major modifiable risk factor for weight management, with strong levels of evidence for protective factors (i.e., dietary fibre, Mediterranean diets) and risk factors (i.e., high energy density, free sugars, sugar sweetened drinks, and Western-type diets) 5,7. Another characteristic of UPFs is that they are obtained after sequences of several processes, such as high-temperature extrusion, moulding, and pre-frying, and include several food additives and industrial ingredients used to imitate or enhance sensory qualities of foods or to disguise unpalatable aspects of the final product; they are also often in contact with synthetic packaging materials for long periods 25. Consistently, several cross-sectional and ecological studies have substantiated a positive association between UPF consumption and obesity 23,35–39, but prospective studies are lacking, as only 2 of them—one in Spain 40 and one in Brazil 41—were conducted; both relied on dietary data from food frequency questionnaires (FFQs) and studied the contribution of UPF to energy intake and therefore did not account for low-calorie and artificially sweetened products. Several indicators of the nutritional quality of the diet were also computed based on average dietary intakes from baseline 24-hour dietary records and were used as covariates: daily nutrient intake (sugar, fibre, sodium, and saturated fatty acid SFA) calculated using the food composition database; consumptions of several food groups (fruit, vegetables, and sugary drinks); and healthy and Western dietary patterns, derived from Principal Component Analysis (see Method D in S1 Appendix).