Faster Insulin in Closed-Loop Pumps: Small but Real Gains

What Was Studied — and Why It Matters

Automated insulin delivery (AID) systems — often called closed-loop or "artificial pancreas" systems — combine a continuous glucose monitor with an insulin pump to automatically adjust insulin throughout the day and night. Researchers wanted to know whether filling these systems with ultra-rapid-acting insulins (like Fiasp or URLi) worked better than standard rapid-acting insulins (like regular insulin aspart or lispro).

The distinction matters because ultra-rapid insulins are designed to start working faster after a dose — which could, in theory, help an automated system respond more quickly to rising blood sugar. This review pooled results from 16 carefully controlled studies involving 664 people with type 1 diabetes to give the clearest possible answer.

What the Researchers Found

The analysis showed that ultra-rapid insulins did produce a small but real improvement in time-in-range (TIR) — the percentage of the day that blood sugar stays within the healthy target zone (roughly 70–180 mg/dL). On average, people using ultra-rapid insulin spent about 1.07% more time in range compared with those using standard rapid insulin.

That might sound tiny, but every extra percentage point in range equals roughly 14 extra minutes per day at a healthy blood sugar level.

Other notable findings included:

• Ultra-rapid insulin users spent 0.35% less time in low blood sugar territory — meaning slightly fewer hypoglycemic dips.
• The benefit was most consistent in adults, in studies lasting more than four weeks, and in systems that automatically correct meal-time doses (bolus correction).
• There was no increase in dangerous events like severe low blood sugar (hypoglycemia) or diabetic ketoacidosis (DKA) with ultra-rapid insulin.

What This Means for Real Patients

If you or your child uses an automated insulin delivery system, this research suggests that switching to an ultra-rapid insulin analogue is a safe option that may offer modest improvement in blood sugar control. The gains are small on a percentage basis, but safe and consistent — particularly for adults using systems with automatic bolus correction features.

It's important to note that "not clinically significant" in research language means the improvement, while real, may not be large enough on its own to change treatment guidelines. Talk to your endocrinologist or diabetes care team about whether switching insulin types makes sense for your specific pump system and lifestyle.

Regardless of which insulin type you use, having reliable supplies on hand is essential. MDS Diabetes makes it easy to manage your continuous glucose monitoring and pump supplies so your AID system can do its job without interruption.

Bottom Line

Ultra-rapid insulins like Fiasp modestly improve time-in-range and reduce low blood sugar episodes when used in automated insulin delivery systems — with no added risk of serious complications. While the benefit is small, it is real and consistent, making this a worthwhile conversation to have with your care team.