"refined carbohydrates are digested leading to a rise in blood glucose levels."

Refined carbohydrates are digested faster, leading to a fast rise in blood glucose levels.

Refined carbohydrates have a higher glycemic index than processed whole grains. That's because of their simple chemical structure, leading to powerful spikes in blood sugar and insulin secretion. This immediate impact can lead to an increased risk for type 2 diabetes, overweight and heart disease.

That would be a working theory.