Efficacy and Safety of Fast-acting Insulin Aspart Compared to NovoRapid® Both in Combination With Insulin Degludec With or Without Metformin in Adults With Diabetes

Fast-acting insulin aspart (faster aspart) will be tested to see how well it works and if it is safe. The study compares 2 medicines for type 1 and type 2 diabetes - faster aspart (a new medicine) and insulin aspart (a medicine doctors can already prescribe). Participants will either get faster aspart or insulin aspart (NovoRapid®) - which treatment is decided by chance. Both medicines will be taken together with insulin degludec. Participants will need to take 1 injection 4 times every day: 3 injections 0-2 minutes before breakfast, lunch and dinner and 1 injection at the same time every day. All study medicines are provided in pens. A pen is a tool to inject insulin under the skin.The study will last for about 7 months (30 weeks). Participants will have 11 clinic visits and 17 phone contacts with the study doctor. At 8 clinic visits participants will have blood samples taken. At 3 clinic visits participants cannot eat or drink (water is allowed) 8 hours before the visits - at 2 of these visits participants will be asked to drink a liquid meal and to stay at the clinic for about 5 hours. Participants will fill in a diary the last 3 days before the visits/phone contacts. Women cannot take part if pregnant, breast-feeding or planning to become pregnant during the study period.