arbohydrates when eaten in large quantities can cause drowsiness and induce sleep. This is a physiological reaction to the way blood sugar levels affect the brain. When carbohydrates are digested they enter the circulation where they causes a rise in blood glucose. This glucose is detected by the pancreas and in response insulin is released. The primary function of insulin is to cause the uptake of glucose to cells to lower blood sugar, but it has other functions. One of these other functions is to cause the uptake of branched chain amino acids to skeletal muscle. The removal of branched chain amino acids from the blood decreases the competition these amino acids have with tryptophan for entry to the brain across the blood brain barrier using the large neutral amino acid transporter (L-type transporter). As a result increased amounts of tryptophan can enter the brain, and this is subsequently converted to serotonin and melatonin. Melatonin then induces sleep by binding to receptors in the brain.
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