What type of insulin has the fastest onset of action?

Rapid-acting insulin is known for its fast onset of action, making it the correct choice for this question. Typically, rapid-acting insulins, such as lispro, aspart, and glulisine, start to lower blood glucose levels within 15 minutes of administration. This quick action is particularly beneficial for managing blood sugar spikes that occur after meals, as these insulins can be taken shortly before eating.

The rapid nature of this insulin type allows for more precise control over blood glucose levels around mealtime, which is crucial for individuals who need to manage their diabetes effectively. Patients using rapid-acting insulin can more closely match their insulin intake with carb intake at meals, leading to better overall glycemic control.

In contrast, long-acting insulin is designed to provide a steady release of insulin over an extended period, thus it does not have a faster onset. Intermediate-acting insulins have a delayed onset and are not as quick as rapid-acting types. Short-acting insulin has a faster onset than long or intermediate-acting types but is still not as rapid as the rapid-acting insulins. Therefore, when considering the speed of action, rapid-acting insulin is the most suitable choice.