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lohborn t1_iy0ucok wrote

Digesting food takes a lot of energy. Your body literally changes where blood is flowing after you eat to send more to your digestive system. That means there is less blood for other things like your muscles.

Your body tells you to slow down.

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T0xicalGr33k OP t1_iy0wivd wrote

Wow that's actually insane. I have never thought about this. Thank you!

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18_USC_47 t1_iy1r1dn wrote

This is also why intense workouts and adrenaline situations cause stomach distress.

Shunting blood away from less immediate things like the stomach and keeping it available for muscles is a survival mechanism. It doesn’t matter if your meal is properly digested if you’re dead in the next few minutes to whatever the threat is.

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smart_guy007 t1_iy3b5m0 wrote

You mean brain gets less blood (oxygen)?

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lohborn t1_iy3tt4o wrote

Research is a little mixed, but it looks like the brain specifically doesn't get less oxygen during digestion. Your brain does coordinate signals telling you to slow down though.

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smart_guy007 t1_iy3tz7w wrote

I have read that we feel sleepy when our brain doesn't get oxygen.

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lohborn t1_iy3w6t6 wrote

That's not the only reason we feel sleepy though.

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HexFyber t1_iy1owka wrote

why is this happening only after a certain age?

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police-ical t1_iy0x02l wrote

It's called postprandial somnolence, and it's not perfectly understood, partly because there's a lot of stuff potentially going on. We know there's a big shift with eating from the "fight or flight" sympathetic nervous system to the "rest and digest" parasympathetic nervous system, and this shift means overall low energy and a drive to reduce muscle use and send blood to the gut instead. There are probably a bunch of other shifts in the brain that contribute, though. Interestingly, chemicals like histamine and orexin that regulate appetite also strongly regulate sleep (i.e. blocking histamine makes you sleepy and hungry.)

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VulcanVisions t1_iy1cv0b wrote

Digestion requires huge energy.

It is diverted away from all other bodily systems, making us feel sleepy.

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