Turkey, Tryptophan & Transmitters

Does eating turkey make you stuffed and drowsy? It must the be tryptophan... or not. Sure there is tryptophan in turkey and tryptophan is the starting point for making some neurotransmitters and hormones, but turkey meat is simply protein and fat. Tryptophan (left) is just one of the twenty amino acids found in most proteins, so the drowsiness after the big Turkeyday dinner is more about the “big” and less about the turkey.

Turkey meat is muscle and muscle, as the diagram shows is made of protein molecules that use energy in the form of ATP to move past each other and contract. We chew up the turkey muscle and our stomach juices contain enzymes (these “proteases” are also proteins) that reverse the process of protein synthesis and produce protein fragments called peptides. The specificity of the proteases in the stomach, e.g. pepsin, results in peptides containing intact heparin-binding domains that are also antimicrobial. In the intestines, a new group of proteases are added by the pancreas and the peptides are further reduced in size and heparin-binding domains are degraded. [Pathogens need heparin-binding domains to bind to the intestines.] The remaining peptides bind to the microvilli of the endocytes lining the small intestines, surface bound peptidases release individual amino acids and transport proteins bring amino acids into the endocytes and on to the blood stream.

In the brain, tryptophan is converted by a series of enzymes into serotonin and the serotonin is stored in secretory vesicles adjacent to the synapse that controls signals between nerves. A nerve action potential moves down the axon from the cell body to the synapse. The change in electrical potential reaching the synapse causes the secretory vesicles to fuse with the cytoplasmic membrane and release the serotonin into the synapse. The serotonin binds to the receptors of the adjacent nerve and starts a new action potential that travels to the next nerve body to repeat the process. The synapse is reset by reuptake or degradation of the serotonin. The degradation product, 5-HIAA, is removed into the blood and excreted in urine.

Turkey tryptophan does get converted into serotonin and high serotonin could make you mellow, but turkey is just like any other meat source of tryptophan. The big meal just makes you groggy, because there is less blood to your brain when the mysenteric blood flow is enhanced for digestion. There may also be a rise in blood sugar as the starch off your plate is rapidly converted into glucose in your blood. The potentially damaging high blood sugar is controlled by a rise in insulin that lowers glucose in the blood by stimulating transport into fat cells for immediate conversion into fat. The starch from the meal is rapidly depleted, blood sugar rises and then sudden falls. The low blood sugar also leaves you groggy.

So it was the size of the meal (decreased brain blood flow) and the sweet potatoes and rolls (starch-induced hypoglycemia) that induced you to kickback on the sofa and pass out with the big game lulling you to sleep. Tryptophan from the big bird is in the background waiting for you to awaken. Before you take the first mouthful, check to make sure that your meal follows the anti-inflammation guidelines. Planning ahead can help you to enjoy a meal that won't be a pain later.