In young adults, including those who are lean, mildly obese, or have well-controlled type 1 diabetes, fitness level (measured by oxygen use) is linked to how well their body handles sugar and blood flow in muscles, but it doesn’t add extra predictive power once other factors are considered.

In young adults—even those with mild obesity or well-controlled type 1 diabetes—how blood flows in small muscle vessels and triglyceride levels help predict how well the body uses insulin to process sugar, showing that both blood vessel health and fat levels matter for insulin sensitivity.

In healthy young adults and those with mild obesity or well-controlled type 1 diabetes, how well their body uses insulin to process sugar is linked to how well insulin improves blood flow in their muscles — and this connection stands on its own, even when other factors are considered.

In young adults who are lean, mildly overweight, or have well-controlled type 1 diabetes, things like BMI or fat levels don’t predict how well insulin improves blood flow in muscles—even though they do predict how well the body uses sugar overall.

In young adults — whether they're lean, mildly overweight, or have well-controlled type 1 diabetes — men and women respond to insulin in similar ways in their muscles and blood flow when body size and muscle mass are taken into account.