The glycemic index affects energy levels after meals by measuring how quickly carbohydrate-containing foods raise blood glucose levels. Foods with a high glycemic index (GI) can cause rapid spikes in blood sugar, followed by quick drops, leading to feelings of fatigue and hunger shortly after eating. In contrast, low GI foods promote a steadier release of glucose, providing sustained energy levels and reducing cravings for unhealthy snacks. For optimal energy management and long-term health, it's beneficial to prioritize consuming low to moderate GI foods, which support stable energy levels and help regulate appetite.