This came up after lunch today in school, and I scoured the site (lazily) for it, but couldn’t seem to find the answer. I’m just wondering why we often get very sleepy a few minutes after eating a meal. My friend said the blood flow is concentrated in the stomach and away from the brain, but I find that kind of vague and not very believable.
Thanks folks.
i’ve always heard that it was because we eat so much damn food that our body has to go into overdrive to digest it, thus making us tired. this is the same reason that we wake up hungry the morning after thanksgiving dinner: our body uses so much fuel to digest, it feels like it needs more fuel by the time its done.
One theory is that blood is shunted away from the brain and muscles to the gut to aid in digestion.
Qadgop, MD
Is digestion dramatically weakened with age? When I used to visit my grandmother at a retirement home I was disturbed by how quickly the old people fell asleep after their meals. It was hard to believe the food was not drugged.
The standard answer (grossly oversimplified) is that the sudden release of sugars into the bloodstream causes the body to realease insulin in an attempt to draw the sugars into the muscles, liver etc. The body overshoots and withdraws too much sugar causing a feeling of lethargy due to lack of energy.
The other assumed contributing factor with high protein meals is that tryptophan entering the brain is converted to serotonin until the brain realises there’s a serotonin overload. Serotonin induces sleepiness so high protein effectively induce tiredness.
My understanding was that high carb, not protein, meals were the main cause of Serotion Sleepiness. Another factor that people rarely bring up is good old satiety. There is a certain amount of stress associated with having a less than optimum blood sugar level. Bringing this back to normal brings on a relative feeling of relaxation. And of course the blood diversion away from the brain to the stomach is a major factor as well.
Since most meals contain some sort of carbohydrates, many of these bonds are broken in the process of digestion. The susequent release of carbon dioxide into the bloodstream is known in medical circles as the “carbonate tide”. This shift in blood gas concentrations effectively induces a mild form of suffocation, thus causing a sense of drowsiness.
For us, this only happens after eating lunch, not dinner or B-fast. Which doesn’t make much sense cause either way, blood is going to the stomach.
Didn’t Cecil do this one? I couldn’t find it doing a search, but I know I read this in one of the books…
Zenster got it slightly wrong. The stomach does not immediately start to digest food once it is eaten – rather, it expands until eating is almost over. Once eating is over, powerful muscles in the upper stomach start grinding the food against the pyloric sphincter at the bottom of the stomach, on the signal of the parasympathetic input into the enteric nervous system. The parasympathetic nervous system also vasodilates the gut blood vessels and vasoconstricts muscles in the extremities. The digestive process is aided by secretion of the famous gastric juices, which contain proteases, other digestive enzymes and of course hydrochloric acid. Hydrochloric acid is secreted by cells in the stomach wall. They make the HCl by splitting carbonic acid (H[sub]2[/sub]CO[sub]3[/sub]) into carbonate and a hydrogen ion (HCO[sub]3[/sub][sup]-[/sup] + H[sup]+[/sup]). The hydrogen ion gets secreted apically towards the stomach lumen with the chloride from salt. The sodium ion and the carbonate get secreted basally into the blood. The sodium carbonate raises the blood pH (makes in more basic), which is sensed in the medullary chemoreceptors in the brain. The brainstem response is to slow respiration (which causes more carbonic acid to buildup in the blood because you are not blowing off carbon dioxide as fast). This happens more with proteinaceous and fatty meals because more gastric juice is secreted to digest it. This is called the “alkaline tide.”
Basically, you make gastric acid. All your base are belong to blood. You slow down to compensate for this.
I am in agreement with Zenster…kinda sorta.
Generally, carbohydrates (which are in virtually all foods that are consumed…okay if you ate cheese and a steak for lunch you wont have the same effects) but since our diets generally consume carbs and sugars (think of that Pepsi or that cheesecake here) you are comsuming carbs/sugars.
If you don’t expend those sugars on a regular basis (meaning you don’t regularly exercise and regularly consume the amount of carbs/sugars with your energy level) your body will heighten it’s insulin to store those. (I hope I have this right, been studying up on this a lot in the last year.)
Anyhow, if you consume more carbs/starches and sugars than you expend in a day your body stores it as fat. This makes (I think I am correct) your insulin rise. If you don’t expend them you result in a peak then a crash known as those afternoon blues.
Try it sometime, eat carbs in the morning (no proteins) and then have a complete protien and fat meal and see what happens – no sugars, no pasta, veggies and a meat or cheese/egg dish. I have done it and notice a big difference in my energy levels in the afternoon.
This is why your momma always told you to eat healthy whole grain foods (lot’s less insulin release) and such.