The Glycemic Index indicates how foodstuff is absorbed by the organism (either quickly or slowly). If the GI is high, the food will be absorbed quickly, and it will stimulate the mechanism that triggers hunger. To avoid this situation, it's best to combine non-starchy veggies and low-glycemic carbs at every meal. You should also include a small amount of healthy fats, which play an important (perhaps ironic) role in weight loss, as they help lower the glycemic index of other foods. Sugary foods are your enemy here, so keep them to an absolute minimum to keep your GI levels low.