When diabetic patients take insulin when to eat is related to the type of insulin injected. If it is a common human insulin injected, such as short-acting or premixed, such as Novolin R, Novolin 30R, you can usually eat only 15-30 minutes after the injection, and if you forget to inject it, you can not have a supplementary injection after the meal. If the injection is rapid-acting or premixed human insulin analogues, such as Novalin and Novalin 30, you can eat immediately after the injection is completed, without waiting for time. If you forget to inject before a meal, you can have a supplementary injection after the meal. Insulin analogues are more convenient and flexible. If it is a long-acting insulin or insulin analogue, it is usually injected subcutaneously before going to bed or waking up in the morning, and it has no relationship with whether you eat or not. Therefore, it depends on the specific type of insulin that is given to decide when to eat.