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I don't know about all the mankind, but I know enough people, who becomes sleepy after their meals. Also, I'm not sure, what kind of food do they consume, but I personally get sleepy almost from any food: sweet, fat, spicy, salty, liquid, tasty, untasty, etc.

Is this phenomenon well known?

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The functions of Parasympathetic nervous system - Rest and digest ! – biogirl Feb 15 '14 at 16:08

The name used frequently for this phenomenon is "Post-lunch dip".

"The post-lunch dip is a real phenomenon that can occur even when the individual has had no lunch and is unaware of the time of day. This dip has its roots in human biology, and may be linked to the size of the 12-hour harmonic in the circadian system. It is certainly exacerbated by a high-carbohydrate lunch, and may be more likely to occur in extreme morning-type individuals."

PubMed Source

Another PubMed source "The 'post-lunch' dip is a bi-circadian phenomenon, largely unrelated to lunch, and worsened by a disturbed prior night's sleep. Despite anecdotal claims of adverse effects of larger lunches on afternoon driving ability, there is little actual driving data to support this belief."

For other reading and research...

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As far as I know it happens due the histamine release after meals. It leads to vasorelaxation and blood flow to the gastrointestinal tract. So, brain does not receive enough blood and you feel sleepy.

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Please add some references for your answer. – biogirl Apr 14 '14 at 17:53

Digestion burns a lot of energy as many muscles enter the mechanism as well as many chemical reactions. Therefore, you feel tired as your body has less energy for other functions than it usually do. I remember a lecture at the university about sciences' history in which they explained an experiment, a long time ago, led on death sentenced men. After a very good meal, one guy was going out for a ride while the other was going to sleep. After 6 hours, they killed both of them : the one who slept had fully digested the meal whereas, for the other, digestion was not complete. They guessed it did not go as well as part of the energy needed for digestion was used for skeletal muscles and that sleeping afer eating helped for a better digestion.

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That is a very biased experiment, to say the least. Why, for example, do people then go for a "digestion walk" and actually feel it helps them to digest? – skymningen Feb 17 '14 at 9:26
@skymninge: pure speculation, they mistake the effects on their metabolism of exercise, for the effects on their metabolism of having completed digestion. Or repeated contraction of the abdominal muscles while walking helps shift wind that they associate with poor digestion. Doesn't really matter why, the conclusions of a study of two people can be explained or waved away with any old crazy theory ;-) – Steve Jessop Apr 19 '14 at 4:18

Source : Here

Sugary foods lead to the production of insulin. Insulin stimulates cells to take up glucose from blood. It also mobilizes tryptophan to brain. Once in brain, tryptophan triggers formation of serotonin, a hormone involved in controlling mood and slumber.

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the best sources are PubMed publications. Any other source are unreliable, especially site not related to any scientistic research and activity. – Ilan Apr 14 '14 at 21:51
@llan Ohk..Will search and add some reliable references. – biogirl Apr 15 '14 at 4:06

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