The researchers fed people 50 grams of carbohydrate in a given food. People also don't usually fast for 12 hours and then only eat one food, right? This is like dry toast without jam, it's popcorn without butter, and then it's not eating anything else for two hours. So when you eat potatoes alone, your blood sugar does one thing. When you eat potatoes with a steak, the fat and protein in that steak slow down your digestion.