Edible insect farming is relatively new and currently small, though rapidly expanding, industry. However, there is still insufficient knowledge about the optimal nutritional requirements of each farmed species in order to reach maximum productivity and to scientifically manage mass rearing strategies so as to reach the highest nutritional quality of insects and derived products. The nutritional composition of edible insects has been surveyed in several review publications (Hawkey et al., 2021; Jantzen da Silva Lucas et al., 2020; Osimani et al., 2017), but a wealth of information is still to be produced on this matter, since there is a considerable lack of knowledge on molecular features related to the absorption and metabolism of feed nutrients as well as to processrelated effects on insect meals quality. In fact, the effects of rearing substrates on insect metabolism have been less well reviewed so far. The term ‘substrate’ generically refers to either the materials directly used for insect rearing and formulated growth feeds. Depending on local regulations in force, according to various governmental departments and various levels of government and competent authorities, different countries consider the exploitation of different substrates as being legal or not, and in some countries, where insects are not considered novel foods, specific regulations on insect-rearing substrates are lacking. For example, in some African and Asian states, a large and easily accessible variety of bio-waste products, such as catering waste and manure, are allowed and used as substrates for insect rearing (Kinyuru and Ndung’u, 2020; Kee et al., 2023; Lähteenmäki-Uutela et al., 2021). On the contrary, certain ruminant proteins, catering waste, and meat-and-bone residues are not permitted as feed substrates under EU legislation; therefore only raw materials of vegetable origin should be used. Exceptions mainly consist in some allowed animal-derived products, such as eggs, milk, and related products, rendered fat or blood products, provided they originate from non-ruminant animals (Regulation (EC) No 999/2001). Although new substrates are being continuously tested, EU legislation regulates at different levels (on general rules: Regulation No 178/2002; Regulation No 852/2004. On farmed animal health and disease management: Regulation (EU) No 2016/429) the production, processing and commercialization of insects and derived products. As a consequence, while on one hand, strict regulations are believed to somewhat limit the rapid expansion of the insect rearing sector, on the other hand, high hygiene standards are essential to ensure the safety and quality of marketed products. In any case, insect farming is currently more developed in Asia, with approximately 26 000– 28 000 metric tons produced per year, followed by Africa and Middle East, who annually produce together 19 000–21 000 tons (Insects raised for food and feed – global scale, practices, and policy: https://rethinkpriorities.org/publications/insectsraised-for-food-and-feed, accessed March 31, 2023), which means that more than 70% of farmed insect production at global level is concentrated in Asia, Africa, and Middle East.