Latest / So That's Why / Why Does Your Gut Affect Your Mood?

Transcript

Why Does Your Gut Affect Your Mood? · So That's Why

• 0:04
  Jen: Welcome to the So That's Why podcast, where we unpack the
• 0:07
  science behind everyday questions.
• 0:09
  I'm Jen.
• 0:10
  Jamie: I'm Chris.
• 0:10
  And I'm Jamie.
• 0:11
  Jen: Okay.
• 0:12
  Here's something that catches most people off guard.
• 0:15
  When you're in a foul mood for no obvious reason, which I'm sure never
• 0:19
  happens to- Never happens … either of you, um, you tend to blame your brain.
• 0:24
  So you'll bla- you'll blame a bra- a bad day, a bad sleep, bad chemistry.
• 0:29
  But a surprising amount of that feeling starts somewhere a lot less glamorous.
• 0:34
  So today, we are talking about why does our gut affect our mood?
• 0:40
  Jamie: I'll be honest, I know a full stomach can make me feel sleepy at
• 0:42
  my desk after lunch, but I didn't think it had opinions on my mood.
• 0:46
  Jen: Mm.
• 0:46
  Chris: Well, it's got far more than opinions.
• 0:48
  It has a direct line to the brain.
• 0:50
  Jen: And we tend to treat mood as something that happens
• 0:53
  entirely upstairs, doesn't it?
• 0:55
  Like I said before, a bit of brain chemistry, maybe a rough night's
• 0:58
  sleep, but your gut and your brain are having a constant two-way
• 1:02
  conversation, and surprisingly, the gut is doing most of the talking.
• 1:07
  Jamie: So your gut isn't sitting there quietly in the background,
• 1:10
  getting on with the job.
• 1:11
  It's sending notes up to head office about how we should be feeling.
• 1:15
  Chris: Pretty much, yep, and how it does this is one of the more
• 1:18
  surprising bits of biology we've ever discussed on this podcast.
• 1:21
  Mm-hmm.
• 1:22
  Jamie: Right.
• 1:23
  So by the end of this, I'll either understand myself better, or I'll
• 1:26
  have a brand-new thing to blame.
• 1:28
  I'm fine with either outcome.
• 1:30
  Jen: Okay.
• 1:31
  Let's start with the scale of this because it is wild.
• 1:35
  Chris: Truly
• 1:36
  Jen: wild.
• 1:36
  Uh, truly wild.
• 1:37
  Your gut contains around, um, 500 million neurons, so that's more nerve
• 1:44
  cells than your entire spinal cord.
• 1:47
  Chris: Yep, and sorry to gross you out with this, but living alongside
• 1:50
  those neurons are, you've got roughly 100 trillion microorganisms.
• 1:55
  So bacteria, uh, fungi, viruses, all together are known as the gut microbiome,
• 2:02
  which you may have heard of, and that community isn't just sitting there.
• 2:05
  It's chemically active and busy all of the time.
• 2:08
  Jamie: 100 trillion.
• 2:09
  That's mind-boggling.
• 2:11
  Jen: I know.
• 2:11
  I can't even comprehend that- Yeah … n- number, you know.
• 2:14
  But you might be th- you might be thinking that your body is gonna be taken over by
• 2:19
  these bacteria, but the balance of that community, it turns out to matter a lot.
• 2:24
  So there was a large study published in 2023, and they found that gut
• 2:30
  dysbiosis, which is when there's a significant imbalance between the helpful
• 2:34
  and the unhelpful bacteria, that was present in around 75% of people that
• 2:40
  were diagnosed with major depression.
• 2:42
  Jamie: 75%.
• 2:43
  So at that point, the gut isn't a minor influence on mood.
• 2:46
  It's basically a cosigner.
• 2:48
  Jen: Yeah.
• 2:48
  Chris: That's right, and to add to that, um, researchers at University College
• 2:52
  London found that people with a lower microbiome diversity reported higher rates
• 2:57
  of anxiety and low mood, even after you take into account other lifestyle factors.
• 3:02
  Jen: Which leaves the obvious question, which proba- people are
• 3:05
  probably thinking, is how does something happening down in your gut
• 3:10
  actually change how your brain feels?
• 3:12
  Chris: So the main line of communication is the vagus nerve, and this vagus
• 3:17
  nerve is a long, branching nerve that runs from your brain stem down
• 3:21
  through your chest into the abdomen.
• 3:23
  It's, kind of wires the gut and the brain directly together.
• 3:26
  It's the direct line that I mentioned earlier.
• 3:27
  Jamie: Mm. So it's, it's a dedicated line between the two.
• 3:30
  Mm-hmm.
• 3:30
  It's not going through reception.
• 3:31
  Chris: Yep, no switchboards involved.
• 3:34
  Um, and here's where things get quite interesting for the fact fans out there.
• 3:39
  That roughly 80% of that communication traffic on that line is heading
• 3:43
  upwards, so from the gut to the brain.
• 3:45
  In this instance, the brain's doing far more listening than it is instructing.
• 3:49
  Jamie: So on this dedicated line, the gut is doing 80% of the calling,
• 3:53
  and the brain mostly just picks up.
• 3:55
  So it's not a conversation.
• 3:57
  The gut keeps leaving voicemails for the brain.
• 3:59
  Jen: And the brain is actually maybe only returning one in five of those voicemails.
• 4:05
  And, you know, trust your gut, it stops sounding like a
• 4:08
  motivational poster, doesn't it?
• 4:10
  And starts sounding more like a wiring diagram.
• 4:13
  Jamie: Yep.
• 4:13
  The saying turns out to be more literal than you'd think.
• 4:16
  Jen: Mm.
• 4:16
  Chris: It does.
• 4:17
  And a lot of what the gut is calling about is neurotransmitter production.
• 4:21
  And here's another one for the fact fans out there.
• 4:24
  Did you know that over 90% of the body's serotonin, which we all know
• 4:27
  is the main mood-setting chemical, is made in your gut, not your brain.
• 4:31
  Did you know that?
• 4:32
  Jen: No.
• 4:33
  Jamie: So the brain takes all the credit for mood, and the gut actually
• 4:36
  does all of the actual manufacturing.
• 4:38
  Jen: Yeah, but there's a subtlety worth getting correct.
• 4:42
  So the te- serotonin made in your gut, it doesn't travel up to your
• 4:46
  brain directly because it can't cross the blood-brain barrier.
• 4:51
  So what it does is it stimulates that vagus nerve, and the nerve tells the brain
• 4:55
  to adjust the mood, appetite, and anxiety.
• 4:58
  So it isn't the serotonin making the trip, it's the message.
• 5:02
  Jamie: So the gut rings ahead and tells the brain what to
• 5:05
  do, and the brain just does it.
• 5:07
  Chris: Near enough, yep.
• 5:08
  And serotonin isn't the only thing it's making.
• 5:10
  So gut bacteria also produce GABA.
• 5:13
  GABA, uh, gamma-aminobutyric acid, which is your main calming
• 5:17
  signal, plus short-chain fatty acids that lower inflammation and
• 5:21
  look after the gut lining itself.
• 5:24
  Jen: And there's also a 2025 study from the, from Duke University, which is pretty
• 5:30
  cool really, because they identified what they're calling a neurobiotic sense.
• 5:36
  So there's specialized cells in the gut lining that can detect specific
• 5:40
  bacterial strains within seconds and relay that message straight to the brain.
• 5:46
  Jamie: In just seconds, the gut's identifu- identifying
• 5:49
  individual bacteria and responding.
• 5:52
  Chris: It's mind-blowing, isn't
• 5:54
  Jen: it, when you think about it?
• 5:54
  It is absolutely mind-blowing.
• 5:54
  And we treat it all as just background noise.
• 5:57
  Mm. But your gut is running the fastest reporting line in the building, and
• 6:01
  never once asks for the recognition.
• 6:04
  Chris: And this matters, doesn't it, because it means that the gut-brain
• 6:07
  link is even more immediate than we've ever thought it was in the past.
• 6:11
  Jen: Yeah.
• 6:11
  And the stress side of this, it's just as important as well,
• 6:15
  because it turns into a loop.
• 6:16
  So when you're under sustained pressure, cortisol rises, and
• 6:21
  cortisol weakens the integrity of the gut lining, and researchers
• 6:25
  call that intestinal permeability.
• 6:27
  Chris: Yeah.
• 6:28
  And once, um, the lining is more permeable, bacterial byproducts
• 6:32
  can slip into the bloodstream, and that triggers an immune response,
• 6:35
  which drives inflammation.
• 6:37
  The inflammation feeds straight into the kind of low mood and anxiety.
• 6:41
  And this increased intestinal permeability is commonly known as
• 6:44
  leaky gut- Mm … which I think a lot of people have heard of.
• 6:47
  And it, this leaky gut is rightly getting a lot of research attention
• 6:50
  at the moment, 'cause it's linked to all sorts of ailments.
• 6:52
  Jen: Sounds pretty horrible too.
• 6:53
  Chris: Yeah.
• 6:54
  Jamie: Yeah.
• 6:54
  So stress damages the gut.
• 6:56
  The damaged gut makes the stress worse, worse, and it goes round and round.
• 7:00
  Jen: Yeah.
• 7:00
  And that's the frustrating elegance of it, and it's also why the link between
• 7:05
  IBS and anxiety isn't a coincidence.
• 7:09
  It genuinely runs both ways.
• 7:10
  So gut inflammation drives the mood symptoms, and the
• 7:14
  stress drives the gut symptoms.
• 7:16
  Jamie: And this is where it gets practical, because it lands differently
• 7:19
  depending on how you actually live.
• 7:21
  Jen: Mm.
• 7:22
  Jamie: Think about anyone in a high-pressure job, living off
• 7:24
  whatever's quickest most days.
• 7:26
  That isn't just a waistline question.
• 7:28
  It's quietly reshaping their microbiome, and through it, their baseline moods.
• 7:33
  Mm.
• 7:33
  Chris: That's right.
• 7:34
  And, and you can see that in food research.
• 7:36
  So diets high in, uh, ultra-processed foods were found to reduce lactobacillus
• 7:42
  and bifidobacterium species.
• 7:44
  These two are the exact strains most linked with steadier
• 7:47
  mood and lower anxiety.
• 7:49
  Jamie: So the convenience food isn't only doing what we already worry about, it's
• 7:53
  also quietly evicting the helpful tenants.
• 7:56
  Jen: Yeah.
• 7:56
  And the helpful tenants, as you describe them, do get pushed out, yeah.
• 8:00
  But the speed works both ways, which is the encouraging bit.
• 8:05
  Um, one 2022 study found measurable shifts in the microbiome after just
• 8:10
  72 hours of meaningful dietary change.
• 8:14
  Jamie: Wow, 72 hours.
• 8:15
  So the thing I assumed would take months to budge, turns around in a long weekend.
• 8:20
  Jen: Mm.
• 8:20
  Chris: I know.
• 8:20
  It's remarkably responsive, isn't it?
• 8:22
  It's, it's crazy.
• 8:23
  And, um, with it, here's a myth worth clearing up.
• 8:25
  Jen: Or busting.
• 8:26
  Chris: So… Oh yeah.
• 8:27
  Actually, the, the myth clearer upper.
• 8:28
  The myth buster sounds better, doesn't it?
• 8:30
  Jen: It doesn't sound as good- No … the myth clearer upper, is it?
• 8:33
  Chris: So probiotics get written off, don't they, as kind of wishful
• 8:37
  thinking- Mm … and lacking evidence.
• 8:39
  But for specific strains at proper doses, the evidence is actually solid.
• 8:43
  So, um, Lactobacillus rhamnosus and Bifidobacterium longum have both been
• 8:49
  shown- Um, to get real reductions in anxiety scores in control trials.
• 8:55
  Mm-hmm.
• 8:56
  So this is due to their positive impact on your gut bi- microbiome.
• 8:59
  So there is method to probiotics that often get written off.
• 9:03
  Jen: Yeah.
• 9:04
  And there was a study in 2020 over… They studied over 1,000 adults, and
• 9:09
  they found that people who regularly ate fermented foods like kimchi, miso, kefir,
• 9:14
  they had measurably lower stress scores, and it held across the ages as well,
• 9:20
  right up from, like, 25 right up to 70.
• 9:23
  Jamie: So it isn't just a thing for the young and the very organized.
• 9:26
  It applies to everyone.
• 9:28
  Jen: Yeah.
• 9:28
  Chris: Yeah, and the bit that I found encouraging is that the same study found
• 9:32
  the benefit was strongest in people whose microbiome diversity started off lower.
• 9:36
  So the people with the most to gain did actually gain the most.
• 9:39
  Jen: Which almost never happens in health research, does it?
• 9:42
  Usually, the people already doing everything right,
• 9:45
  they get the biggest reward.
• 9:47
  Jamie: So the further behind you've started, the more there is to win back.
• 9:51
  Mm.
• 9:51
  Chris: Yep, good news, right?
• 9:52
  Always good to spread the cheer.
• 9:53
  Jen: It is.
• 9:54
  Chris: So what does this look like day to day?
• 9:58
  The most evidence-backed starting point is prebiotic fiber.
• 10:01
  So oats, uh, leeks, garlics, onions, um, a bit of chicory,
• 10:06
  slightly underripe bananas.
• 10:08
  These are all foods that help the, to feed the bacteria- Yeah … that can
• 10:12
  make helpful short-chain fatty acids.
• 10:14
  Jamie: So the unglamorous answer is eat more onions.
• 10:19
  Chris: No.
• 10:19
  I can't, can't do onions.
• 10:20
  Devil's food.
• 10:21
  Not, not for me.
• 10:21
  Jen: But ess- essentially, Jamie, yes, if you don't mind onions.
• 10:25
  Jamie: Love onions.
• 10:26
  Jen: Um, but then there are also fermented foods, um, to partner with that.
• 10:30
  So a small daily serving of something live, like a natural yogurt with
• 10:35
  an active culture, kefir, maybe a spoon of sauerkraut, some miso.
• 10:40
  You know, even modest amounts, they seem to shift and make a difference
• 10:44
  to diversity within a few weeks.
• 10:46
  Jamie: And a spoonful of miso in hot water takes you about 45 seconds to do.
• 10:51
  Jen: Just a spoonful of- Doesn't sound as good as spoonful
• 10:52
  Chris: of sugar, does it?
• 10:53
  Yeah, just a spoonful of miso helps the medicine go down.
• 10:55
  There
• 10:55
  Jamie: we go.
• 10:56
  Chris: Yeah, and omega-3 is worth a mention here too, and
• 10:58
  not only for the brain directly.
• 11:00
  So omega-3 helps support that gut lining, and it calms the background
• 11:04
  inflammation sitting at the center of this whole kind of stress loop.
• 11:08
  Jen: Mm.
• 11:09
  Jamie: And look, I'll be straight about this.
• 11:10
  We sell supplements for a living, and the honest headline of this
• 11:14
  episode is still mostly, eat real food and go to bed on time.
• 11:18
  I'm oddly fine with that.
• 11:19
  Jen: It's the least salesy health advice imaginable.
• 11:22
  Chris: Yeah.
• 11:23
  I think we managed to get the marketing involved here.
• 11:24
  Jamie: Oh, yeah.
• 11:25
  And the dose of it is going to be different for everyone, presumably.
• 11:28
  If two people is, eat the exact same week of food, they don't
• 11:32
  end up with the exact same gut.
• 11:34
  Chris: That's right.
• 11:34
  They, they really don't, and it's a good thing to flag.
• 11:37
  So everyone's starting microbiome is different.
• 11:39
  So the same yogurt won't do the identical job in two people.
• 11:43
  Mm. It's the direction of travel, uh, is what is reliable, not a fixed
• 11:47
  result by a kind of certain day.
• 11:49
  Jamie: Mm. So nobody should panic if their neighbor feels
• 11:51
  brilliant on kefir and they don't.
• 11:54
  Different starting point, different timeline.
• 11:57
  Chris: That's the right way to hold it.
• 11:58
  But there's one caveat, and, um, in my official capacity as Captain Sensible.
• 12:03
  If anyone is dealing with persistent low mood alongside symptoms like, uh, bloating
• 12:09
  or irregularity, IBS-type pattern, it's genuinely worth raising with a doctor
• 12:14
  because there are real clinical interests now in targeted probiotic protocols.
• 12:20
  So it's not just a lifestyle chat anymore.
• 12:21
  There are things people can do.
• 12:22
  So keep that in mind.
• 12:24
  Jen: And this, it all reframes the whole mental health conversation, doesn't it?
• 12:28
  'Cause we've spent a long time treating mood as a purely brain-based
• 12:32
  thing when the gut is clearly a major author of the chemistry involved.
• 12:37
  Jamie: And it ties into so much we already half know.
• 12:40
  Jen: Mm.
• 12:41
  Jamie: Sleep, stress, what we eat.
• 12:44
  It's all the same machinery, just looked at from a different angle.
• 12:47
  Jen: Mm.
• 12:48
  Chris: It is, and, and it all goes round and round, doesn't it?
• 12:50
  So poor sleep disrupts the microbiome, a disrupted microbiome lowers serotonin
• 12:54
  signaling, lower signaling dents your mood, low mood lifts cortisol, and
• 12:59
  cortisol goes back and damages the lining.
• 13:01
  It's kind of a, a very tight loop that repeats.
• 13:04
  Jen: But the cheering thing, I'll admit I needed cheering after the cortisol part-
• 13:09
  Yeah … is how responsive the gut is.
• 13:11
  So unlike the rest of the body, it can shift in days to weeks.
• 13:16
  You know, that's quick feedback once you start being a little bit
• 13:19
  more consistent with your diet.
• 13:21
  Jamie: Which means we've basically built a very thorough scientific case-
• 13:24
  Mm-hmm … for eating properly, sleeping, and not living in a permanent panic.
• 13:29
  None of which is new.
• 13:30
  All of which I now do slightly more of having heard the why.
• 13:34
  Chris: Yeah, and that's the whole point of the why, isn't it?
• 13:36
  So rules on their own don't stick, but the reasons do.
• 13:39
  Jen: Mm.
• 13:39
  Jamie: So go on then.
• 13:40
  Why does our gut affect our mood?
• 13:43
  Jen: Because your gut is home to trillions of microorganisms making the
• 13:47
  transmitters and chemical signals your brain relies on to set how you feel,
• 13:53
  including over 90% of your serotonin.
• 13:56
  Chris: And it sends all of that straight up to the brain along the vagus nerve,
• 14:01
  with the gut doing most of the talking.
• 14:03
  So in this relationship, the brain is mainly the listener.
• 14:07
  Jen: So that's why your mood isn't only in your head.
• 14:11
  A surprising amount of it begins a good deal further south
• 14:14
  Jamie: Yes.
• 14:15
  So next time I feel flat on a Sunday evening for no reason, I'll be aiming
• 14:19
  my suspicions a bit lower than usual.
• 14:21
  Jen: On that note, that's it for this week.
• 14:23
  Make sure you hit that subscribe button.
• 14:26
  We're unpacking the science behind everyday questions each week.
• 14:30
  Tell us in the comments what you'd like us to explore.
• 14:33
  Thanks for geeking out with us.
• 14:35
  But for now, that's it from me.
• 14:37
  Chris: That's it from me.
• 14:38
  Jamie: That's it from me.
• 14:39
  Jen: Bye for now