The glycemic index — a measure of how fast carbohydrates are turned into sugar — offers an answer (see «How the glycemic index works»). (health.harvard.edu)
The glycemic index describes how fast a carbohydrate is converted to glucose in your body. (fitnessandpower.com)
In the meantime, it prevents the fat - burning process (it's a storage hormone, after all), driving you to eat and making you crave what will bring your blood sugar back up — aka more processed fast carbohydrate snacks. (mindbodygreen.com)