The document discusses the Glycemic Index, which ranks foods based on how quickly they raise blood sugar levels after consumption. A high GI means blood sugar rises quickly, while a low GI means it rises slowly and stays steady. High GI foods break down rapidly, causing blood sugar fluctuations, while low GI foods break down slowly for stable blood sugar levels. However, a low GI food is not necessarily nutritious if it contains unhealthy ingredients like saturated fat or lacks nutrients. An overall balanced diet and exercise are most important for health.