The glycemic index (GI) is significant in nutrition as it measures how quickly carbohydrate-containing food raises blood glucose levels. Foods with a low GI release glucose gradually, leading to sustained energy and better appetite control, while high GI foods can cause rapid spikes and drops in blood sugar. Understanding GI can inform healthy dietary choices, particularly for individuals with diabetes or those looking to manage weight. Balancing low and high GI foods can optimize overall health and energy levels.