You already know you should eat more fruit, veg and fibre. You've heard it a hundred times. But do you know why? Not in a vague "it's good for you" way — I mean the actual mechanism by which a bowl of lentils changes what's happening in your lungs, your joints or your brain.
That gap is exactly what my guest on this episode has spent his career closing. He's a respiratory immunologist whose research group at the Centenary Institute and the University of Technology Sydney has spent more than 25 years studying how inflammation drives disease progression — in asthma, type 1 diabetes, arthritis, Alzheimer's, Parkinson's and more. And the trail led him, unexpectedly, to the gut.
The Clue That Changed His Research
About a decade ago he sat in a conference talk on chronic obstructive pulmonary disease — emphysema, as most people know it — and heard an epidemiologist describe something that stopped him cold. People with inflammatory bowel disease appeared markedly more likely to have COPD, and people with COPD markedly more likely to have inflammatory bowel disease. The specific multiple he recalled from that talk is a figure cited in his field rather than something I'd present as settled, but the direction of the finding was unmistakable: the gut and the lung are talking to each other.
At roughly the same time, sequencing technology matured to the point where researchers could actually read the gut microbiome — all the bacteria living there, the genes they carry, and the compounds they produce. Suddenly the question became answerable.
What his group and many others keep finding is that the gut microbiome and its metabolites look markedly different in disease than in health — and that holds across very different diseases. Which raises the obvious next question: is the gut driving what happens elsewhere in the body?
Why Everything in Your Gut Reaches Everywhere Else
The logic here is beautifully simple once you see it. You eat. Food travels to your intestines. There it becomes fuel for your microbiome, which metabolises and breaks it down. Those products get absorbed through the gut wall into circulation — and from there they reach every cell, tissue and organ you have.
As he put it, anything that ends up in your gut has the potential to affect everywhere else in your body.
And here's the lever: specific foods can only be used by specific bacteria. Eat one thing and you grow out one population. Eat something else and you grow out another. So the food on your plate genuinely reshapes which bacteria thrive and therefore which compounds circulate through you. Eat fibre and you feed the bacteria that ferment it — and in doing so they produce metabolites that appear to be anti-inflammatory. Eat fruit and vegetables and you grow out different populations producing different beneficial compounds.
This is the part I love as a clinical nutritionist. It takes "eat your veggies" out of the realm of nagging and puts it into the realm of biochemistry.
Which Fibre? The Honest Answer
I asked whether his research has pinpointed particular types of fibre — soluble, insoluble, a mix. I appreciated that he didn't pretend to more certainty than he has.
The field isn't yet sure which exact fibres matter most; a lot of studies are running right now to work it out. The current thinking in his group leans toward insoluble fibres, on the reasoning that they persist longer in the gut and so have more opportunity to grow out the bacteria that ferment them usefully. But he was explicit that this is a working view, not a conclusion.
My practical read: don't wait for the field to settle before you act. Variety is the strategy that doesn't require knowing the answer. Different plants carry different fibres and feed different bacteria, so a wide range of vegetables, fruit, legumes, whole grains, nuts and seeds hedges your bets better than any single "best" fibre ever could.
Prebiotics vs Probiotics — It Depends on You
Here's a point that deserves more airtime than it gets. For a prebiotic to work, the beneficial bacteria it feeds have to already be living in your gut. If they're not there, there's nothing to grow. That's the argument for pairing the two: take in the bacteria and the fuel they need.
But it gets more complicated. Can an introduced strain actually establish itself and out-compete what's already in residence? There's even a genuinely controversial line of thinking about whether you'd need to clear out some existing bacteria first to make room. He named that as controversial and unresolved — and I'd add plainly: this is not something to attempt on your own initiative. It's a research question, not a protocol.
He was also candid that decades of probiotic research have produced results that are sometimes reasonable but rarely stunning — and his view is that's because we haven't yet nailed down which bacteria are genuinely beneficial and precisely how they work. Once we do, diets could be targeted far more precisely.
His picture of the future: sequence an individual's microbiome, see what's present and what's missing, map that against their conditions, and work out how to shift it. We're not there yet. The hard unsolved problem is cause and effect — whether the microbiome changes seen in a given disease are driving it or resulting from it. Almost certainly it's some of each, and untangling which is which is the work.
Why Modern Diets Are Part of the Story
We've co-evolved with our food for a very long time, and our microbiota evolved alongside us. So what happens when the food changes faster than we do?
Asthma, he noted, has risen sharply across the globe in recent decades — a rise that tracks alongside the rise in ultra-processed food. I'd be careful here: tracking together isn't proof of cause, and he's the first to say the mechanisms are still being worked out. But the supporting evidence is hard to dismiss. Growing up on a farm with exposure to animal microbiomes is strongly associated with less asthma and less severe asthma. Antibiotics in childhood, which clear out the microbiome, are associated with higher risk of developing it.
To be clear, that is not an argument against antibiotics — they save lives and you should take them when your doctor prescribes them. It's an argument for taking the microbiome seriously as something worth rebuilding afterwards.
Inflammatory bowel disease has followed a similar upward trajectory over a similar window. His conclusion is that moving back toward the foods we co-evolved to eat — and away from heavily processed ones — is likely to work in our favour.
Sleep, Stress and Movement Are In This Too
I asked about the rest of the picture, because food never operates alone.
His research doesn't focus here, but plenty of others' does, and the association is established: stress, poor sleep and disrupted circadian rhythms all come with changes in the gut microbiome. The details — which bacteria, which metabolites — are still being mapped, because the field is barely a decade old.
What I find genuinely hopeful is the direction he raised in return. If the relationship runs both ways, then eating well and sleeping well might modify the microbiome and lower stress at once. That's a cycle you can break into from more than one side, which is good news if diet feels like the hardest door to open right now.
Movement matters for an almost mechanical reason: exercise gets blood circulating through the fine capillaries serving your lungs and your gut, which affects how metabolites travel around the body.
How You Eat, Not Just What You Eat
This was my favourite part of the conversation, and it costs nothing.
There's a well-worn rule of thumb that it takes around twenty minutes for your stomach to signal fullness to your brain. Treat the number loosely — the point stands. Eat fast and you've got a long window in which to consume a great deal more food than you need before the signal ever arrives. Slow down, actually taste the food, and satisfaction turns up much earlier in the meal.
He pointed to the populations that live longest — in Okinawa, around the Mediterranean — who take long, unhurried lunches and eat until they're satisfied rather than until they're full. That's a meaningful distinction and worth sitting with.
And I want to underline how he framed all of this, because it's not the usual tone. This isn't about giving up everything you like and choking down things you don't. Eating well, not overeating, and genuinely enjoying your food can be a thoroughly positive change — one you look forward to rather than endure.
Key Takeaways
- Your gut is not a closed system. What your microbiome produces enters your bloodstream and reaches every organ you have.
- Feed variety, not a single superfood. Different plants feed different bacteria, and the research hasn't crowned a best fibre — so breadth is the smart bet.
- Prebiotics need a resident population to work on. Fuel without the bacteria to use it doesn't achieve much.
- Cut back on ultra-processed food — the association with inflammatory conditions is the strongest practical signal in this field.
- Sleep, stress and movement all shift the microbiome, so start with whichever lever you can actually move this week.
- Slow your meals down. Eat until satisfied rather than full — the cheapest intervention here, and completely free.
What I take from this conversation is a strong endorsement of what I see every day in practice: individualisation. We each carry a different genome and a different microbiome, shaped by what we've eaten, what our parents ate, and the life we've lived. There is no single correct diet, and anyone selling you one should give you pause. At me&my wellness I work with the whole picture — food, movement, sleep, stress and the gut sitting quietly at the centre of it — because that's how the body actually behaves.
And if you take one thing away, let it be this: you eat several times a day, every day. Few levers in health give you that many chances to do something useful.
This article is general information, not medical advice. If you're managing a respiratory condition, inflammatory bowel disease, or any diagnosed illness, talk to your doctor before making significant dietary changes, and keep them informed about what you change.
Want to go deeper on this? Book a free 30-minute discovery call with Anthony at meandmywellness.com.au