What foods are slow-release? Several tools have been designed to help answer this question. The glycemic index (GI) tells you how quickly a food turns into sugar in your system. Glycemic load, a newer term, looks at both the glycemic index and the amount of carbohydrate in a food, giving you a more accurate idea of how a food may affect your blood sugar level. High GI foods spike your blood sugar rapidly, while low GI foods have the least effect.