Why do we get tired after eating?

Giles Yeo crunched down on Pius' question... Giles - Ah, that's an interesting question. I think what a lot of people think is as you're eating all the blood rushes from your head to your stomach in order to begin the digestion process.

Chris - You speak for yourself, Giles.

Giles - That's a myth. So the reason why you get tired after, that's not a myth, that actually does happen. It's not because of blood rushing from all parts of you body to your stomach. But I think the best way we can understand it is when you have a large mass of food within you gut and gastrointestinal tract, it turns on something called the 'parasympathetic nervous system.' So there is a nervous system which when you smack your face - ouch! - that kind of nervous system, but the autonomic nervous system which govern your unconscious bits of the things that happen.

Now there are two portions to that. There's the sympathetic nervous system the 'fight or flight' syndrome and there is the parasympathetic system which is actually the 'feed or breed' take a chill pill, sit down and slow down.

Chris - I heard it called 'rest and digest.' I hadn't heard it called 'feed or breed,' that's a new one on me but I like it.

Giles - So what happens is, as far as we understand it, this large mass of food, postprandially, after you eat, tilts your autonomic nervous system towards the parasympathetic so, therefore, causing you to feel tired. Now the reasons why, like once again we don't actually now, but evolutionarily you can imagine you need some time to sit and actually digest stuff before you can actually get up and run again. I don't know but that's probably the reason why.