Many people are aware that high carbohydrate foods can make them drowsy. The reason for this is well understood and relates to the way that carbohydrate foods cause the release of insulin. Insulin is a hormone that is responsible for pushing both glucose and amino acids into cells. When a high carbohydrate meal is consumed, blood insulin levels go up, and glucose and some amino acids are transported from the blood into cells. In particular, the branched chain amino acids, that are responsible for muscle building, leave the blood. This causes drowsiness, because the branched chain amino acids compete for transport into the brain with the amino acid tryptophan. The high insulin levels therefore facilitate the transport of tryptophan into the brain. Tryptophan is converted to serotonin in the brain, and then to melatonin. Melatonin is a hormone that induces sleep. Therefore, as more tryptophan passes into the brain due to carbohydrate consumption, the amount of sleep inducing melatonin increases, causing drowsiness.
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