You are probably eating more than your body needs. It could also be if you are eating foods that are heavy in carbs, like pasta and breads. There are a few foods like turkey that contain a chemical called tryptophan that allegedly make you feel more tired after eating. My suggestion is to start with eating a little less than normal each meal, and see if that won't kill your energy levels after meals. You can also try to eat foods that increase your metabolism. Spicy foods are good for boosting metabolism, also lemon juices and cayanne pepper are good for keeping you awake. One other trick is to drink ice cold water along with your meal, The cold water will fill you up faster, help you digest the food more quickly, you will eat less food, and if it's ice cold it will be refreshing and keep your senses stimulated.
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