South Korea Study: Combo Insulin Beats Basal-Only for Some T2D Patients

A Study from South Korea Shows a Smarter Way to Match Insulin to Your Biology

A study from South Korea, conducted at Seoul National University Hospital, reveals that not all type 2 diabetes patients respond equally to standard basal insulin therapy — and that a combination insulin product may work better for a specific group of patients whose bodies struggle to produce enough of a key gut hormone called GLP-1.

What Was This Study About?

Researchers enrolled 55 adults with type 2 diabetes (average age 65, 40% male) who were already on basal insulin but showed a telltale sign of overbasalization — a situation where fasting blood sugar is well-controlled, but overall A1C remains stubbornly high. This mismatch signals that mealtime blood sugar spikes are the real problem, not overnight glucose levels.

Participants were randomly assigned to one of two insulin regimens for 20 weeks, then switched to the other in a crossover design:

• IDegAsp (Ryzodeg®) — a once-daily combination of long-acting insulin degludec and rapid-acting insulin aspart
• Insulin glargine (Lantus®/Basaglar®) — a standard long-acting basal insulin

Key Findings

The combination insulin IDegAsp outperformed basal insulin glargine on A1C reduction:

• A1C dropped to 7.8% with IDegAsp versus 8.0% with insulin glargine
• The difference of 0.21 percentage points was statistically significant (P=0.031)
• Continuous glucose monitoring (CGM) confirmed that daytime glucose levels were meaningfully lower with IDegAsp
• Hypoglycemia rates were similar between both treatments — meaning the benefit came without added low-blood-sugar risk

Critically, the patients who benefited most from IDegAsp were those with a blunted GLP-1 response — meaning their gut didn't release enough of this appetite- and insulin-regulating hormone after meals. This is a common but underrecognized pattern in longstanding type 2 diabetes.

What Is GLP-1 and Why Does It Matter?

GLP-1 (glucagon-like peptide-1) is a hormone your intestines release after eating. It signals your pancreas to produce insulin and suppresses blood sugar spikes after meals. Many people with type 2 diabetes — especially those who've had it for years — have a diminished GLP-1 response. This is exactly why GLP-1 receptor agonists like semaglutide (Ozempic®, Wegovy®) are so effective. But for patients who can't tolerate those medications or need insulin anyway, this study suggests IDegAsp may fill a similar gap.

Putting the Numbers in US Terms

The study's participants entered with an average fasting plasma glucose of 103 mg/dL and an A1C of 8.3% — numbers many American patients will recognize from their own lab reports. The American Diabetes Association (ADA) targets an A1C of below 7.0% for most adults, making an 8.3% starting point a clinically meaningful area of concern. A 0.21% A1C improvement, while modest, can translate to measurable reductions in long-term complication risk.

Why This Matters for US Patients

Millions of Americans with type 2 diabetes are on basal insulin and still not meeting their A1C goals. This South Korean research adds to a growing body of global evidence that overbasalization is underdiagnosed — and that switching to a combination insulin like IDegAsp (available in the US as Ryzodeg® 70/30) may be a smarter next step than simply increasing basal insulin dose. Additionally, this study introduces a biological marker — GLP-1 response — as a potential guide for choosing insulin therapy, moving diabetes management closer to personalized medicine. Talk to your endocrinologist about whether your fasting glucose and A1C levels suggest overbasalization, and whether your GLP-1 response has ever been evaluated.

Original Study

Jang, Hong, Yang. "Glycemic Benefit of Insulin Degludec/Insulin Aspart Compared to Basal Insulin in Type 2 Diabetes Mellitus Associated with Impaired Glucagon-Like Peptide-1 Response: A Randomized Crossover Trial." Diabetes & Metabolism Journal, 2026. PMID: 40808225. DOI: 10.4093/dmj.2024.0741