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Why Do We Feel Tired After Eating? · So That's Why

• 0:04
  Jen Oliver: Welcome to the So that's Why podcast where we unpack the
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  science behind everyday questions.
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  I'm Jen.
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  Chris Smith: I'm Chris.
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  Jamie Eynon: And I'm Jamie.
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  Jen Oliver: Right.
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  Today we're getting into something that I can guarantee has
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  happened to at least one of us.
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  Why do we feel tired after eating?
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  You know that feeling You've had lunch, you sit back down at your desk
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  and 20 minutes later your eyelids weigh about 10 kilos each, and you
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  can barely remember your own name.
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  Jamie Eynon: It's the workplace epidemic nobody talks about.
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  You go into lunch as a functioning human being and come out the other
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  side like you've been mildly sedated.
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  I've seen entire meetings derailed by it.
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  Everyone's sitting there nodding along, but nobody's actually
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  processing a single word.
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  Chris Smith: It's even got a proper name, which is postprandial.
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  Somnolence, but basically a fancy way of saying food cover.
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  Jen Oliver: That sounds much more dignified than I need to lie face down
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  on the sofa 'cause I've eaten my lunch.
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  But seriously, there's some brilliant science behind this, and it turns out
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  that your brain has specific neurons whose job it is to keep you awake,
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  and food literally switches them off.
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  On top of that, your gut is producing raw materials for the same hormone
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  that helps you fall asleep at night.
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  Jamie Eynon: So eating lunch is basically like taking a mild sleeping pill.
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  That explains the 2:00 PM meeting that we've all been through,
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  Chris Smith: and what's interesting is how common and how impactful this is.
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  So research shows the post-lunch dip affects the majority of us in some
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  degree, and it typically hits hardest about 30 minutes to an hour after meals.
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  For some people, it can linger for hours,
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  Jamie Eynon: and it's not just about comfort.
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  There's a real pro productivity cost here.
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  If you think about how many people are making decisions driving operating
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  equipment in that post-launch window.
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  Understanding what's happening and how to manage it actually matters
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  beyond just feeling a bit groggy.
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  Jen Oliver: And that's a really good point.
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  You know, studies have found that cognitive performance measurably
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  drops jaw in the window and the reaction times slow down.
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  Your attention drifts and your ability to take in new information, it decreases.
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  So if you've ever tried learning something right after lunch and
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  felt like nothing was sticking.
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  Well, it was real.
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  Chris Smith: No, you're totally right.
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  And the thing is, this persistent or severe tiredness after meals can sometimes
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  signal something worth paying attention to, like blood sugar regulation issues.
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  Mm-hmm.
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  So while occasional post meal drowsiness is completely normal, if
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  it happens heavily after every meal and it really is impacting your day.
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  It's worth trying to understand exactly what's going on,
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  Jen Oliver: which is exactly what we're gonna do.
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  So Chris, when I eat a meal, particularly one with a decent amount of
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  carbohydrates, what's actually happening inside my body to make me feel sleepy?
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  Chris Smith: Okay, so there are actually multiple mechanisms working together here.
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  It's not just one thing.
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  So let's start with what happens when carbohydrates hit your system.
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  When you eat carbs, your blood glucose rises.
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  And your pancreas releases insulin to move that glucose into your cells for energy.
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  So far, so normal, right?
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  Jen Oliver: Right.
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  That's like standard blood sugar regulation.
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  But the insulin's doing something else too, isn't it?
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  Chris Smith: Exactly.
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  And here's the clever bit.
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  Insulin triggers your muscles to absorb certain amino acids from your blood.
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  Okay.
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  Specifically a group called large neutral amino acids, and there's another amino
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  acid called tryptophan that competes with these four transport route to the brain.
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  So when insulin clears those competing amino acids out, the tryptophan
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  suddenly has a much easier path across that blood brain barrier.
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  Jen Oliver: And what people probably don't know is that tryptophan
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  is the precursor to serotonin.
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  So once it reaches the brain, it gets converted into serotonin, which
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  influences sleep and wakefulness.
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  And some of that serotonin then becomes melatonin, and that's the
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  hormone that signals your body.
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  It's time to sleep.
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  Jamie Eynon: So your lunchtime pasta is essentially manufacturing sleep hormone.
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  Your body's running a melatonin production line and you didn't know.
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  Chris Smith: Mm, absolutely.
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  Yeah.
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  That's a good way of looking at it.
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  But there's another really important mechanism happening at the same
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  time, your brain has specific neurons called orexin neurons in an area
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  called the lateral hypothalamus.
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  These neurons are one of your brain's primary stay awake signals.
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  And research has shown that when blood glucose rises after a meal, it
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  actually silences those orexin neurons.
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  Jen Oliver: You've got a double hit.
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  You're increasing the ingredients for sleep hormones while simultaneously
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  turning down the volume on your brain's wakefulness signal.
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  And it's quite a combination to deal with.
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  Chris Smith: It is.
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  And as always, there's more.
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  So after a meal, your body shifts into what's called parasympathetic
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  nervous system mode, often described as rest and digest.
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  So your heart rate slows slightly, your blood pressure drops a touch,
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  and your digestive system ramps up.
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  That whole shift promotes the state of calm and relaxation that
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  naturally overlaps with drowsiness.
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  Jamie Eynon: That makes sense.
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  Makes sense of something you'll have noticed.
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  It's not just tiredness, it's specific kind of heaviness.
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  Mm. You don't feel sleepy the way you do at bedtime.
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  It's more like your whole body downshifts and it's worse than when you eat.
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  It's worth when you eat a massive meal versus something lighter.
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  The bigger the meal, the harder the, uh, the shift.
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  Chris Smith: That is exactly right.
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  And there's a reason for that.
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  So for larger calorie dense meals, like particularly those high end, both fat and
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  carbs, the body releases pro-inflammatory cytokines, and these are small signaling
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  proteins and elevated levels are associated with fatigue and sleepiness.
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  So the bigger and richer the meal, the stronger that response.
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  Jen Oliver: Then there's also the role of gut hormones.
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  So when you eat meals high in fat and protein, the gut releases
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  hormones that are satiety signals that tell your brain you're full.
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  But these hormones have also been linked to increased drowsiness
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  Chris Smith: they have.
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  And so after we eat, our body doesn't rely on just one
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  process to feel full or relaxed.
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  Instead, several systems are working together.
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  Insulin signaling, uh, gut hormones and even inflammatory signals.
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  And one important piece is that orexin, which is that brain chemical
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  that keeps us awake and alert.
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  So after eating a orexin activity is reduced, which contributes to that
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  sleepy, relaxed post-meal feeling.
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  So the bigger and richer the meal, the stronger that response tends to be.
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  Mm.
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  Jamie Eynon: No wonder we can, can't keep our eyes open after a big Sunday roast.
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  Jen Oliver: Mm-hmm.
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  Chris Smith: Yep.
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  That's pretty common.
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  Uh, but something really important to layer in here is the circadian rhythm.
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  So your body has a natural dip in alertness in the early afternoon,
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  so roughly between one and 3:00 PM And this happens regardless
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  of whether you've eaten or not,
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  Jen Oliver: Which means for most people, lunchtime actually collides directly
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  with the preexisting biological dip.
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  Um, but interestingly, research has shown that meals don't
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  actually cause the afternoon slump.
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  They amplify it.
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  And one study found that eating increased the length of an afternoon
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  nap, but it didn't initiate it.
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  Jamie Eynon: That's interesting because it also showed up in studies
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  of night shift workers when they ate during their shifts at night.
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  They experience more tiredness than when they didn't eat.
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  So it's not just an afternoon thing.
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  Eating at any time of day or night can trigger this response.
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  It's just that lunchtime is when it stacks on top of your body's clock.
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  Chris Smith: Yeah, exactly.
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  And what you eat matters enormously.
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  So high glycemic carbs like white bread, uh, white rice, sugary foods, they cause
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  a faster sharper blood sugar spike, which drives that a bigger insulin search.
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  So more tryptophan entering the brain and a. More dramatic orexin shutdown.
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  The whole cascade is amplified in that case.
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  Jen Oliver: Whereas meals that combine complex carbs with protein, healthy
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  fats and fiber, they slow down that gluc glucose absorption, and that
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  produces a more gradual response and a less dramatic sleepiness.
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  But it also varies between people too.
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  So some people experience what's called reactive hypoglycemia, where the insulin
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  response overshoots after a high carb meal driving blood sugar below normal
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  levels, and then that causes fatigue, shakiness, and brain fog that goes beyond
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  that typical post post-meal drowsiness.
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  Chris Smith: Yeah, totally.
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  And there was a longstanding, uh, theory that digestion diverts blood away from the
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  brain to the gut, reducing oxygen supply.
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  That's been partially challenged though, and one study actually
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  found that blood flow to the brain may increase after meals, and the
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  brain is remarkably good actually at protecting its own blood supply.
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  So while blood redistribution does happen during digestion, it's unlikely to be a
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  main driver of that post meal drowsiness.
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  Jen Oliver: Okay, so given all these mechanisms, what can
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  people actually do about it?
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  Because I can imagine most of our listeners can't exactly take a nap
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  after their lunch on a Tuesday.
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  Say,
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  Chris Smith: yeah, that'd be nice, wouldn't it?
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  Um, so the, the single most impactful thing is the meal composition.
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  So building meals with complex carbohydrates, lean protein,
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  uh, healthy fats, and fiber.
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  That will slow down digestion and blunt those blood sugar spikes.
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  So basically swap the white bread for whole grain, add some protein
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  and vegetables, and that alone can make a noticeable difference
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  to how alert you feel afterwards.
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  Jamie Eynon: Um, and portion size is a big one too.
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  I know people who eat a huge lunch because they've skipped breakfast and
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  then wonder why they've completely wiped, are completely wiped up
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  by two o'clock, spreading your intake more evenly through the day.
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  Means you are not triggering that massive insulin and
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  hormone response all in one go.
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  Jen Oliver: Mm-hmm.
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  Chris Smith: And that's a really practical point actually.
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  So those smaller balanced meals produce a gentle hormone response overall and place
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  less demand on your digestive system.
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  Jen Oliver: And here's one that's really well supported,
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  going for a post-meal walk.
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  Even a short, gentle walk after eating, it can improve your blood
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  circulation, stimulate glucose uptake by your muscles, and counteract
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  that parasympathetic drowsiness.
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  And you don't need to go for a run just 10 to 15 minutes of moving around.
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  It can make a big difference.
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  Jamie Eynon: Loads of cultures build this into their daily routine already.
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  Think of the Italian Pajata and the Post did a walk in Mary Many.
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  Asian countries.
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  Um, we've somehow in the UK and in Europe, well in, in Northern Europe,
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  somehow engineered this out of our day by eating at our desks and going
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  straight back to our computer screens.
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  Jen Oliver: Mm.
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  Chris Smith: I love the way you pronounced that Italian word, which I won't try
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  to do myself, but that was great.
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  Um, bright light exposure is another one backed by research.
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  So bright white light in the afternoon has been shown to reduce that
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  post-lunch dip and improve alertness.
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  So if you can get outside or sit near a window after lunch.
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  Natural light helps counteract that circadian dip.
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  Jen Oliver: And as always, hydration plays a role as well.
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  If you're dehydrated, that can compound fatigue.
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  So staying hydrated throughout the day, it supports the whole picture too.
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  Jamie Eynon: And probably worth saying if you are relying on a big coffee straight
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  after lunch to get through the afternoon, that might work short term, but it can
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  interfere with your sleep later, um, which just makes the next day dip worse.
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  It's a cycle that feeds itself if you're not careful.
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  Jen Oliver: So what strikes me is how this connects to everything
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  else we've covered on this podcast.
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  Sleep quality, energy levels, even mood.
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  They're all intertwined with how and what we eat.
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  Chris Smith: Absolutely.
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  And if you're not sleeping well, which of course we've explored in detail
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  in the sleep episode, you are more susceptible to that afternoon dip.
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  So poor sleep amplifies the natural circadian low point so
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  that food coma hits even harder.
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  Jamie Eynon: And if your diet isn't giving you the right nutrients
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  overall, your energy regulation is compromised before you even go to lunch.
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  The post-meal dip is really just one piece of a much bigger picture when it
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  comes to how you feel throughout the day.
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  Jen Oliver: It's a good reminder, isn't it, that these health topics,
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  they're not isolated chapters.
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  How you eat at lunch connects to how you sleep last, slept last night,
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  which connects to your energy levels for exercise, which connects back
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  to sleep quality and understanding.
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  One piece helps us manage the whole picture.
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  Jamie Eynon: So why do we actually feel tired after eating?
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  Chris Smith: It's because eating particularly carbohydrate
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  rich meals triggers a cascade of biological responses.
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  Insulin drives tryptophan into your brain where it's converted
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  to serotonin and melatonin.
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  Rising blood glucose silences your brain's wakefulness, neurons, your
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  nervous system shift into rest and digest mode, and gut hormones and inflammatory
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  signals all add to that drowsy feeling.
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  Layer on top of that, your body's natural afternoon dip and you've got the
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  perfect recipe for a full on food coma.
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  Jen Oliver: So that's why that 2:00 PM meeting feels like such a
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  struggle and why a balanced lunch and a short walk afterwards can
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  genuinely change your afternoon.
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  Your body's doing exactly what it's designed to do.
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  The trick is working with it, not against it.
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  That's it for this week.
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  Make sure you hit that subscribe button.
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  We're unpacking the science behind everyday questions each
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  week, and tell us in the comments what you'd like us to explore.
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  Thanks for geeking out with us, but for now, that's it from me.
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  Chris Smith: That's it from me, and that's it from me.
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  Jen Oliver: Bye for now.