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Livestock production is facing the feed-food competition, use of natural resources, and environmental sustainability. To address these issues, the use of food leftovers in animal nutrition could satisfy the principles of circular economy. Among the different food leftovers, former food products (FFPs) consist mainly of unsold/defective food from industrial production (i.e., bread, croissants, biscuits, chips). FFPs can be classified in sugary confectionary FFPs (FFPs-C) and salty bakery FFPs (FFPs-B). The aim of this study was to assess the impact of the inclusion of FFPs into post-weaning diet of piglets on the fatty acid profile of subcutaneous adipose tissue and on serum metabolites. Thirty-six post-weaning female piglets (Large White × Landrace, BW 8.52 ± 1.73 kg) were assigned to a standard diet (CTR), or with a 30% replacement (wt/wt) of conventional cereals with FFPs-C or FFPs-B for 42 days. Growth performance and feeding behavior were measured. Subcutaneous abdominal fat samples were collected from 12 selected piglets after slaughtering. Gas chromatography was performed on feed samples from control diet and experimental diets and on adipose tissue samples. Untargeted metabolomics was performed on blood samples (d 0 and d 42) using UHPLC/MS-MS. Data were analyzed with the software MetaboAnalyst (version 5.0). The inclusion of FFPs did not alter growth performance or feeding behavior. The CTR diet had greater PUFA concentrations than FFPs diets. In FFPs diets, the fatty acid profile was equally distributed among SFA, MUFA, and PUFA. The ω-6/ω-3 ratio was greater in FFPs-C diets than CTR and FFPs-B diets. The subcutaneous adipose tissue showed no differences between groups for SFA concentrations. The MUFA concentrations were reduced in CTR compared with FFPs groups, whereas PUFA concentrations were reduced in FFPs-C group compared with FFPs-B and CTR groups. The ω-6/ω-3 ratio was less in FFPs-C group compared with CTR and FFPs-B groups. The untargeted metabolomics identified a total of 104 metabolites, with 2 significantly different between groups. Specifically, the serum concentration of theobromine and caffeine was greater in FFPs groups compared with CTR. To conclude, piglets were able to rebalance the fatty acids profile despite the differences observed in the diets. The metabolic status was not strongly altered by the inclusion of 30% FFPs in the diet. Thus, FFPs could be safely applied in postweaning pig diets. Further studies are needed to assess the effect of FFPs on pig physiology and metabolic status in growing phase pigs and for a longer feeding time. (funded by ASSO Project-Regione Lombardia). [ABSTRACT FROM AUTHOR]