Any foods rich in carbohydrates, like toast or pretzels, cause our blood sugar to spike, which in turn triggers our body to produce insulin in order to bring it back down. This is why sometimes after eating a meal full of carbs you feel energized briefly, but then quickly crash into a tired state of mind. Insulin also brings tryptophan and serotonin to the party, which are two chemicals in the brain that help us feel relaxed.