Is coffee bad for me? A clinical nutritionist's take

Gut Health
Written by Sophie Kirk

The quick answer: for most women, coffee isn't bad for you. It can even be good for your gut. What matters is how you have it: eat first, keep it before 2pm, and notice how it makes you feel.

Put the guilt down, not the latte

If you've ever felt a little guilty sipping your morning coffee, this one's for you. Somewhere along the way, coffee got a bad reputation in the wellness world. Cut it out, swap it for something green, quit caffeine for your hormones. It's a lot. My honest take as a clinical nutritionist? For most women, coffee can absolutely be part of a healthy gut. It just comes down to how you're having it. So instead of a list of rules, I'd love you to ask yourself a few gentle questions. See if any of these sound familiar.

"One coffee and I'm buzzing"

Caffeine nudges up cortisol and adrenaline, your stress hormones. For most of us, that just feels like a lovely little lift.But if your stress response (your HPA axis) is already running hot from work, poor sleep or a very full plate, that extra nudge can tip you from alert into wired. Think racing thoughts, jitters, or a heart that feels a bit too fast.
Some people are simply more sensitive to caffeine, partly because their body clears it more slowly. That's completely ok. Your nervous system comes first.
If that sounds like you, a few gentler options:

  • Matcha or green tea, which give a softer lift

  • L-theanine, an amino acid found naturally in tea, which may help take the edge off

  • Decaf, which still counts for your gut bacteria (more on that soon)


"I can't function without it"

This one surprises a lot of people: caffeine doesn't actually give you energy. It works by blocking adenosine, a chemical that builds up through the day and makes you feel sleepy. Caffeine sits in its spot, so you don't feel the tiredness. But the tiredness is still there.

Your real energy comes from food, sleep and rest. And over time, your body adapts to daily caffeine. The more you lean on coffee, the less it lifts you, until it's mostly just getting you back to normal. so, if you’re finding you can’t stay awake without your coffee, it might be worth asking what's leaving you so tired in the first place.


"Coffee is my breakfast"

Cortisol is naturally at its highest in the morning. One of its jobs is to nudge your blood sugar up, so you've got fuel to start the day. Coffee on an empty stomach can add to that. In one small study from the University of Bath, a strong black coffee before a sugary breakfast drink, after a rough night's sleep, made the blood sugar rise around 50% bigger.

So why does that matter? When your blood sugar rises more, your body releases more insulin to bring it back down. That's often followed by a bigger dip. Hello 10am crash, shakiness, irritability and a sudden need for biscuits.

Keeping those morning rises gentler matters even more if you're working on insulin resistance or PMOS.

The easy fix is fuel first, then coffee. Even something small with protein before your cup, like Greek yoghurt or eggs on toast, can help.


"I can't go to the toilet without it"

Coffee really does get things moving. It stimulates your bowel, which is why so many of us need the bathroom not long after that first cup. Totally normal.

But if you genuinely can't go without it, you might be more constipated than you think. Your coffee could be doing a job your gut should be able to do on its own. This is something we want to be investigating.

Fibre, water, movement and a bit of routine can help your gut find its own rhythm again. And if things still feel stuck, it's worth looking into properly.


The good news for your gut

Now for my favourite part!!

Coffee is rich in polyphenols, plant compounds your gut bacteria love. A 2024 study in Nature Microbiology found regular coffee drinkers carry 4.5 to 8 times more of a gut bacterium called Lawsonibacter asaccharolyticus than people who don't drink coffee.

The best bit? The link showed up in decaf drinkers too. So it's likely coffee's other compounds doing the work, not the caffeine. Researchers are still working out exactly what this bacterium does for us, but it's a lovely reminder that coffee is a plant food.

Coffee is also linked with lower rates of liver disease, including fatty liver.


When and how much

A few gentle tweaks can help your coffee work with you, not against you.

  • Keep it before 2pm. Caffeine has a half-life of around 5 hours, so roughly half of a 2pm coffee is still in your system at 7pm. If your sleep's patchy, that's the first cup to move earlier.

  • Mind the timing if your iron is low. In one study, a cup of coffee with a meal cut iron absorption by 39%, and having it an hour after eating didn't help. If your iron needs some love, try having your coffee between meals instead.

  • Know your numbers. Up to 400mg of caffeine a day is considered safe for most adults, or 200mg if you're pregnant. But in one Australian study, a single café espresso shot ranged from 25 to 214mg. So counting cups tells you less than you'd think.


Notice how it feels

The research is only half of it. The other half is you. Next time you have your coffee, notice how you feel an hour later. Focused and steady? Lovely. Wired, shaky or starving? That's your body telling you something.

Anxiety, low energy and sluggish bowels can all have lots of causes. If you've tried a few tweaks and things still don't feel right, it's worth looking into properly with someone who can see the whole picture.

And if you'd like a hand, bring your latte to our first chat.


Coffee FAQs

Is coffee bad for your gut?

For most people, no. Regular coffee drinkers carry more of a gut bacterium called Lawsonibacter asaccharolyticus, and coffee's polyphenols feed your gut bacteria. Some people do find it triggers reflux or loose stools, so notice how yours feels.

Is it bad to drink coffee on an empty stomach?

It's not dangerous, but it can make your blood sugar harder to manage. In one small study, a strong coffee before a sugary breakfast drink made the blood sugar rise around 50% bigger. Eating first is an easy swap.

Why does coffee make me need to poo?

Coffee stimulates your bowel, so needing the bathroom soon after your first cup is normal. If you can't go without it, though, you might be more constipated than you think.

Does coffee affect iron absorption?

Yes. In one study, a cup of coffee with a meal cut iron absorption by 39%, and having it an hour after eating didn't help. If your iron is low, have your coffee between meals.

How much caffeine is too much?

In Australia and New Zealand, up to 400mg a day is considered safe for most adults, or 200mg if you're pregnant. A single café espresso shot can hold anywhere from 25 to 214mg, so it's worth knowing your café.

Is decaf good for your gut too?

It looks that way. The link between coffee and Lawsonibacter asaccharolyticus showed up in decaf drinkers too, so the benefit likely comes from coffee's other compounds, not the caffeine.

Do I need to wait 90 minutes after waking for my first coffee?

There's no good evidence for that rule. Adenosine, the chemical that makes you sleepy, is actually at its lowest when you wake up. Eating before your coffee and keeping it before 2pm matter more.


About the author

Sophie is a Clinical Nutritionist and the founder of Hello Glow Nutrition. She is dual-degree qualified and has completed specialist gut microbiome training.

She works with women on gut health, blood sugar and metabolic health, with Telehealth options available across Australia and New Zealand.

Sources

Sophie Kirk