The glycemic index is significant in meal planning as it measures how carbohydrate-containing foods affect blood sugar levels. Foods with a high glycemic index can cause rapid spikes and drops in blood sugar, potentially leading to energy crashes and increased hunger. Conversely, low-glycemic foods provide a slower, more stable release of energy, promoting satiety and better blood sugar control. Understanding glycemic index helps individuals make informed food choices, particularly for those managing conditions such as diabetes, as it can enhance diet effectiveness and overall health.