Black soldier fly larvae (Hermetia illucens) fed spent coffee grounds: NMR metabolomics

Black soldier fly (Hermetia illucens, BSF) larvae efficiently convert organic residues into nutrient-rich biomass for use as animal feed, but the metabolic consequences of using challenging substrates are poorly understood. Spent coffee grounds (SCG) is a widely available byproduct with high fibre content and bioactive compounds that can limit nutrient accessibility. In this study, the effects of incorporating SCG into the BSF larval diet were tested at three inclusion levels (50, 75, 100%), using growth metrics and nuclear magnetic resonance (NMR) untargeted metabolomics. Metabolomic profiling uncovered diet-driven shifts in central metabolism, with larvae fed SCG exhibiting markers of intensified fatty acid and amino acid catabolism (acetylcarnitine, carnitine, β-alanine), while compensating for the impact on glycolysis compared to the control. Together, these results demonstrate that SCG supplies usable nutrients but imposes metabolic challenges that limit larval growth. Our findings inform the sustainable valorisation of SCG in insect bioconversion and advance the understanding of metabolic resilience in BSF larvae when faced with suboptimal diets.