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Introduction Former foodstuffs (FPPs) generate large amounts of waste, consisting mainly of unsold products (i.e., bread, croissants, biscuits, cakes, dough). FPPs have many names in different parts of the world: dried bakery products, bakery meal, bakery waste, former food, bread meal (Pinotti et al., 2021). These products can be distinguished into two categories: sugary FFPs from confectionary production (FFPs-C) and salty FFPs from bakery production (FFPs-B). This study aimed to investigate the possibility to partially replace standard ingredients with two different types of FFPs and their effects on fatty acid profile (Saturated fatty acids, SFA; Monounsaturated fatty acids, MUFA; PolyunsatuAbstracts / Animal - Science Proceedings 13 (2022) 241–510 392 rated fatty acids, PUFA; and x-6/x-3 ratio) of ubcutaneous adipose tissue and on selected metabolites (choline, and two metabolites associated with FFPs consumption, namely theobromine and caffeine) in post-weaning piglets. Material and Methods Thirty-six post-weaning female piglets were randomly assigned to a standard diet (CTR), or diets in which traditional ingredients were partially replaced by the 30% inclusion (w/w) FFPs-C or FFPs-B diets for 42 days. The nutrient composition of the three experimental diets met NRC (2012) requirements and were iso-energetic and iso-nitrogenous. Growth performance and feeding behaviour were measured and published in Luciano et al. (2021). Feed samples fatty acids profile was performed by gas-chromatography. Blood samples were collected at day 42. All samples have been analyzed at UNITECH OMICs (UNIMI, Italy) using ExionLCyAD system, connected to TripleTOFy6600 System (SCIEX) equipped with Turbo VyIon Source with ESI-Probe. Untargeted metabolomics analysis was performed in positive and negative mode. Subcutaneous abdominal fat samples were collected from 12 piglets after slaughtering (day 42 – authorized by Italian Ministry of Health – N405/2019-PR). Approximately 50.0 g of subcutaneous-fat was collected, packed in 50 mL falcon, frozen in liquid nitrogen, stored at -80 °C until further analysis. Fatty acids analysis was performed by gas-chromatography. Data were analysed using IBM SPSS Statistics software. Fatty acids composition for experimental diets (CTR, FFPs-C, FFPs-B) and subcutaneous-fat samples were analysed using one-way analysis of variance (ANOVA) to compare means. Correlation studies were performed by Pearson’s correlation method to study the association between the fatty acids in subcutaneous-fat samples and blood-metabolites. Results and Discussion The three diets did not evidence any effect (P > 0.05) on growth performance. No differences (P > 0.05) were found in ADG, ADFI, and FCR (Luciano et al., 2021). In the CTR diet, PUFA represented by itself about 50% of fatty acids, while in the two experimental diets (FFPs-C and FFPs-B) saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids were equally distributed (Figure 1A). When x-6 and x-3 ratio was considered, the ratio was higher in FPPs-C compared to CTR and FFPs-B (10,17%, 8,87% and 9,81%, respectively). Fatty acid profile of subcutaneous adipose tissue samples has shown no significant differences (P < 0.05) between groups for SFA, with the only exception for tendency (P > 0.15) observed for SFA between CTR and FFPs-B tissue samples. A lower percentage of MUFA were observed in CTR compared to FFPs-C and FFPs-B group (Figure 1B). In the case of PUFA, the FFPs-C group shows the lowest value compared to FFPs-B and CTR groups. When x-6 and x-3 ratio was considered, a slight decrease in the ratio (P < 0.05) was recorded in subcutaneous adipose tissue of animals fed with FFPs-C diet. An high (R > 0.80) positive correlation between choline, and two metabolites associated with FFPs consumption, namely theobromine and caffeine, and MUFA was found (data not showed). Conclusion and Implications The results indicated that despite some differences observed in compound feed, piglets were able to rebalance the fatty acids profile. The main differences were observed for MUFA and PUFA in adipose tissue of CTR animals compared to FFPs animals. Indeed, CTR animals showed lower MUFA compared to FFPs animals, while PUFA were higher in CTR animals vs. FFPs-C animals. Furthermore, MUFA has shown high and positive correlation with choline, theobromine and caffeine, associated with FFPs consumption. Future studies will unravel the synergisms among ex-food-based diets and adipogenesis, lipogenesis, and body fat accumulation in pigs. Funding The present study is part of the project: ‘‘Sustainable feed design applying circular economy principles: the case of former food in pig nutrition (Susfeed)‘‘ funded by Fondazione Cariplo (Italy, Ref: 2018-0887).