Post-prandial somnolence

Post-prandial somnolence, sometimes referred to colloquially as food comacite web|title=Urban Dictionary: Food Coma|url=http://www.urbandictionary.com/define.php?term=food+coma|accessdate = 2008-06-12] , is a state of sleepiness or lassitude following a meal. Post-prandial somnolence has two components - a general state of low energy related to activation of the parasympathetic nervous system in response to nutrients in the gastrointestinal tract, and a specific state of sleepiness caused by hormonal and neurochemical changes related to the rate at which glucose enters the bloodstream and its downstream effects on amino acid transport in the central nervous system.

Physiology

Parasympathetic Activation

In response to the arrival of food in the stomach and small intestine, the activity of the parasympathetic nervous system increases and the activity of the sympathetic nervous system decreases.cite web|title=The Autonomic Nervous System|url=http://microvet.arizona.edu/Courses/VSC401/autonomicNervous.html| accessdate = 2008-06-12] This shift in the balance of autonomic tone towards the parasympathetic system results in a subjective state of low energy and a desire to be at rest, the opposite of the fight-or-flight state induced by high sympathetic tone. The larger the meal, the greater the shift in autonomic tone towards the parasympathetic system, regardless of the composition of the meal.

Insulin, Large Neutral Amino Acids, and Tryptophan

When foods with a high glycemic index are consumed, blood glucose levels rise rapidly, and in individuals with normal carbohydrate metabolism, insulin levels rise concordantly to drive glucose in to the body's tissues and maintain blood glucose levels in the normal range.cite |author=DJ Jenkins et al|title=Glycemic index of foods: a physiological basis for carbohydrate exchange.|publisher=Am J Clin Nutr 34; 362-366|date=1981] Insulin stimulates the uptake of valine, leucine, isoleucine, and tyrosine in to skeletal muscle, but not uptake of tryptophan. This lowers the ratio of these large neutral amino acids in the bloodstream relative to tryptophancite journal | author = Wurtman RJ, Wurtman JJ, Regan MM, McDermott JM, Tsay RH, Breu JJ | title = Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios | journal = Am. J. Clin. Nutr. | volume = 77 | issue = 1 | pages = 128-32 | year = 2003 | pmid = 12499331 | doi = | issn = | url = http://www.ajcn.org/cgi/content/abstract/77/1/128] , making tryptophan preferentially available to the large neutral amino acid transport at the blood-brain barrier.cite web|title=Proceedings of the National Academy of Sciences: The LNAA Transport at the Blood Brain Barrier|url=http://www.pnas.org/cgi/content/abstract/96/21/12079|accessdate = 2008-06-12] Uptake of tryptophan by the brain thus increases. In the brain, tryptophan is converted to serotonincite journal | author = Fernstrom JD, Wurtman RJ | title = Brain serotonin content: increase following ingestion of carbohydrate diet | journal = Science | volume = 174 | issue = 13 | pages = 1023-5 | year = 1971 | pmid = 5120086 | doi = 10.1126/science.174.4013.1023 | issn = ] , which is then converted to melatonin. Increased brain serotonin and melatonin levels result in sleepiness that has been objectively measured.cite journal | author = Afaghi A, O'Connor H, Chow CM | title = High-glycemic-index carbohydrate meals shorten sleep onset | journal = Am. J. Clin. Nutr. | volume = 85 | issue = 2 | pages = 426-30 | year = 2007 | pmid = 17284739 | doi = | issn = |url = http://www.ajcn.org/cgi/content/full/85/2/426]

Myths about the Causes of Post-Prandial Somnolence

Cerebral Blood Flow and Oxygen Delivery

Although the passage of food into the gastrointestinal tract results in increased blood flow to the stomach and intestines, this is achieved by diversion of blood primarily from skeletal muscle tissue and by increasing the volume of blood pumped forward by the heart each minute. The flow of oxygen and blood to the brain is extremely tightly regulated by the circulatory system and does not drop after a mealcite web|title=Anesthetist: Vascular Autoregulation|url=http://www.anaesthetist.com/physiol/basics/autoreg/Findex.htm#index.htm| accessdate = 2008-06-12] , and is not a cause of post-meal sleepiness.cite journal | author = Bazar KA, Yun AJ, Lee PY | title = Debunking a myth: neurohormonal and vagal modulation of sleep centers, not redistribution of blood flow, may account for postprandial somnolence. | journal = Med Hypotheses. | volume = 63 | issue = 5 | pages = 778-82 | year = 2004 | pmid = 15488646 | doi = | issn = |url = http://www.ncbi.nlm.nih.gov/pubmed/15488646]

Turkey and Tryptophan

Certain foods, such as soybeans, sesame and sunflower seeds, and certain cheeses, are high in tryptophan. Although it is possible these may induce sleepiness if consumed in sufficient quantities, this is not well studied. A common myth holds that turkey is especially high in tryptophancite web|title=About.com: Does Eating Turkey Make You Sleepy? | url=http://chemistry.about.com/od/holidaysseasons/a/tiredturkey.htm | accessdate = 2007-08-17] cite web|title=Howstuffworks.com: Is there something in turkey that makes you sleepy? | url=http://home.howstuffworks.com/question519.htm | accessdate = 2007-08-17] cite web|title=Chemistry.org: Thanksgiving, Turkey, and Tryptophan | url=http://www.chemistry.org/portal/a/c/s/1/feature_ent.html?DOC=enthusiasts%5Cent_tryptophan.html | accessdate = 2007-08-17] , resulting in sleepiness after it is consumed, as may occur at the traditional meal of the North American holiday of Thanksgiving. However, the tryptophan content of turkey is comparable to chicken, beef, and other meatscite web|title= USDA National Nutrient Database for Standard Reference, Release 20 | |publisher= United States Department of Agriculture | author = Joanne Holden, Nutrient Data Laboratory, Agricultural Research Service | url=http://www.ars.usda.gov/nutrientdata | accessdate = 2007-10-02] and does not result in higher blood tryptophan levels than other common foods.

Alcohol

When alcohol is consumed with a meal, this may contribute to sleepiness after the meal, but is a nonspecific response to alcohol consumption and can occur independent of eating.

References