Within-Person Variation in Ultra-Processed Food Consumption Is Associated with Total Daily Energy Intake

Background/Objectives: Important gaps remain in understanding the association between ultra-processed food (UPF) consumption and same-day energy intake. This study aimed to expand the understanding of how within-person variation in UPF consumption is associated with total energy intake. Methods: Nationwide, representative dietary survey data from 38,854 participants (≥10 years old) in the 2017–2018 Brazilian Household Budget Survey food intake module were analyzed. These cross-sectional repeated-measures data were used to estimate within-person differences in energy intake between two days of food consumption. Mixed models were applied to examine the associations between the presence and energy share of UPFs in the diet and total daily energy intake. Results: Among participants who consumed UPFs on only one of the two days (n = 8055), daily energy intake was higher on the day when UPFs were consumed than on the day when UPFs were not consumed (1699 kcal vs. 1530 kcal; p < 0.001). On average, among all participants (n = 38,854), a 10 percentage-point increase in UPF energy share on a given day was associated with an increase of 39 kcal in energy intake over the day. We found statistically significant effect modification by sex (p = 0.024) and age group (p < 0.001). Supplementary analyses suggest that the association between UPF energy share and total energy intake is consistent with partial replacement of non-UPF by UPF and is unlikely to reflect differences in food quantity or energy density. Conclusions: Among participants who consumed UPFs on only one of the two days, the day with UPF consumption was associated with higher total daily energy intake than the day without UPF consumption. A higher within-person UPF energy share was also associated with higher total daily energy intake. Understanding the association between UPF consumption and same-day energy intake can inform public health strategies aimed at reducing excessive energy intake.