Weekend Read · Week 4 · 11 min read · Reviewed against peer-reviewed evidence, October 2026
The short version
This week is about feeding the bacteria in your gut, and they mostly eat what you can't digest: fibre. Most Australian adults don't get enough of it. Higher-fibre diets are linked with lower rates of heart disease, type 2 diabetes and bowel cancer. Eating a wide variety of plants, and adding fermented foods, are two of the most promising ways to look after your gut bacteria, though the research on both is still young.
Gluten, coffee and alcohol step out from Monday to Friday. That isn't a detox, and gluten isn't bad for everyone. It's a short pause so that when each one comes back in Week 5, you can notice how it sits with you.
Most of your gut bacteria live on the food you don't digest
Your large bowel is home to a huge community of bacteria, often called the gut microbiome. Most of what you eat is absorbed before it gets that far. What reaches them is the part your body can't break down: fibre, plus a type of starch that slips past digestion, called resistant starch.
That's where the interesting part happens. Your gut bacteria ferment fibre and resistant starch into compounds called short-chain fatty acids, mainly acetate, propionate and butyrate. Butyrate is the preferred fuel for the cells lining your bowel, and these compounds help with blood flow and fluid absorption in the colon (Topping & Clifton, 2001).
Measuring this inside a living bowel is hard, so much of the detail comes from stool samples and animal studies. But the basic picture, that you feed your bacteria and they feed your bowel, is well established.
Most Australian adults fall short on fibre
The National Health and Medical Research Council sets an adequate intake of 25 grams of fibre a day for women and 30 grams for men, the amount for healthy bowel function (NHMRC). A higher target applies for lowering chronic disease risk.
When researchers analysed the most recent national nutrition survey, the typical Australian adult was eating about 21 grams a day. Only 28% of adults reached the adequate intake, and fewer than one in five reached the higher target (Fayet-Moore et al., 2018).
Fibre is linked with longer, healthier lives
The biggest look at this question was funded in part by the World Health Organization and published in The Lancet in 2019. Researchers pooled 185 long-term observational studies, covering just under 135 million person-years of data, and 58 clinical trials (Reynolds et al., 2019).
People who ate the most fibre had a 15–30% lower risk of dying from any cause or from heart disease than people who ate the least. They also had lower rates of coronary heart disease, stroke, type 2 diabetes and bowel cancer. The benefits were greatest at about 25–29 grams a day. In the clinical trials, eating more fibre lowered blood pressure and total cholesterol.
Most of that is observational, so it shows a link, not proof. But more fibre went with lower risk in a steady dose-response pattern, and the trials pointed the same way. The authors rated the evidence as moderate quality, which in nutrition science is about as good as it gets.
Variety may matter as much as volume
You've probably heard you should eat "30 plants a week". Here's where that number actually comes from.
In the American Gut Project, a citizen-science study, more than 10,000 people, mostly from the US, UK and Australia, mailed in stool samples and filled out a survey. One question asked: "In an average week, how many different plants do you eat?" People who answered "more than 30" had more diverse gut bacteria than people who answered "fewer than 10", including more of the bacteria thought to make short-chain fatty acids (McDonald et al., 2018).
Two honest notes. This is observational and self-reported, and people who eat 30 plants a week probably do other things differently too. And 30 was simply the top box on the survey. Nobody tested 25 against 35. It's a nudge toward variety, not a magic threshold. The idea behind it makes sense, though: different bacteria break down different fibres, so a wider mix of plants feeds a wider mix of bacteria.
Fermented foods did something fibre didn't, in one small trial
This is the result that surprises most people.
In 2021, a team at Stanford randomly assigned healthy adults to one of two diets for ten weeks: a high-fibre diet or a high-fermented-food diet, with 18 people in each group. The fermented group ate things like yoghurt, kefir, kimchi and other fermented vegetables, building up from less than one serve a day to about six (Wastyk et al., 2021).
The fermented-food group's gut bacteria became steadily more diverse. And 19 of the 93 inflammatory markers the researchers measured in their blood went down. The high-fibre group, who roughly doubled their fibre to about 45 grams a day, didn't see a rise in diversity over the same period, though their bacteria gained more of the enzymes needed to break down fibre.
With 36 people, this is an early, small study. It's a reason to add some ferments this week, not a reason to drop fibre. If you'd like more on inflammation, our article Sugar and inflammation: what the science actually says goes deeper.
Why gluten, coffee and alcohol step out for five days
This isn't a detox. Your liver and kidneys do that job every day. And gluten isn't bad for everyone. Most people digest it without any trouble.
What five days off gives you is a clean comparison. Coffee, alcohol and bread or pasta are things most of us have daily without thinking. When they come back in Week 5, you can notice how each one sits with you. Does the second coffee make you jittery? Does wine change how you sleep? Does a big bowl of pasta leave you bloated or fine? There's no right answer. The point is that you'll know.
It also makes room on the plate for buckwheat, quinoa, brown rice, potatoes, lentils and more vegetables, which is exactly where the fibre and variety come from.
A word on coeliac disease
Coeliac disease is a medical condition, diagnosed with blood tests and confirmed by a specialist. The tests only work reliably while you're eating gluten (Coeliac Australia). Five days off won't matter much. But if you suspect gluten is a problem for you, see your GP and get tested before you cut it out long term, not after.
About that coffee headache
If you drink coffee daily, you may get a headache or feel foggy at first. That's caffeine withdrawal. In experimental studies about half of people got a headache, usually starting 12 to 24 hours after the last cup and lasting two to nine days (Juliano & Griffiths, 2004). Cutting back over the weekend can soften it, and a pot of peppermint or rooibos tea keeps the ritual.
Go slow: more fibre can mean more wind at first
Here's the part gut-health posts often skip. When you suddenly feed your bacteria more, they make more gas. In the Stanford trial, both groups built up over four weeks rather than all at once. Even so, the high-fibre group noticed softer stools, and the fermented-food group reported more bloating (Wastyk et al., 2021).
So build up over the week. Add one new high-fibre food or ferment every day or two, drink plenty of water, and back off if you're uncomfortable. A little extra wind is normal. Pain isn't.
If you have irritable bowel syndrome (IBS) or follow a low-FODMAP diet, take extra care. Some well-known high-fibre foods, including onion, garlic and legumes, are common IBS triggers. Check with your GP or a dietitian before you increase them.
The evidence map
A snapshot of the studies behind this article. "Strong" means a systematic review or meta-analysis with a consistent result. "Moderate" means good-quality individual studies or expert reviews. "Emerging" means early or small studies. "National data" means Australian government or national survey figures.
| Theme | Study | Strength | Finding |
|---|---|---|---|
| Fibre and health | Reynolds et al., 2019 | Strong | Highest fibre eaters had 15–30% lower risk of death and several chronic diseases than the lowest; benefits greatest at 25–29 g a day. |
| How bacteria use fibre | Topping & Clifton, 2001 | Moderate | Gut bacteria ferment fibre and resistant starch into short-chain fatty acids; butyrate fuels bowel cells. |
| Australian fibre intake | Fayet-Moore et al., 2018; NHMRC | National data | Typical adult intake about 21 g a day; only 28% of adults meet the adequate intake. |
| Plant variety | McDonald et al., 2018 | Emerging | People reporting more than 30 plants a week had more diverse gut bacteria than those eating fewer than 10. Observational. |
| Fermented foods | Wastyk et al., 2021 | Emerging | In 36 adults, a high-fermented-food diet raised microbiome diversity and lowered 19 inflammatory markers; high fibre didn't raise diversity in 10 weeks. |
| Cooled rice | Sonia et al., 2015 | Emerging | Chilling cooked rice overnight raised its resistant starch and lowered the blood-sugar response in 15 adults. |
| Caffeine withdrawal | Juliano & Griffiths, 2004 | Strong | Headache in about half of people; symptoms typically last two to nine days. |
| Menopause and the gut | Peters et al., 2022 | Emerging | Postmenopausal women trended toward less diverse gut bacteria than premenopausal women. Observational. |
How to feed your gut this week
Everything below fits the Week 4 rules: no gluten, coffee or alcohol Monday to Friday, and sugar, sweeteners and fruit still out.
1. Count your plants, loosely
Stick a note on the fridge and tally each different plant food the first time you eat it this week. Vegetables, legumes, nuts, seeds, whole grains, herbs and spices all count, and each one counts once, however often you eat it. That's our simple house rule, not a scientific standard. Don't aim for 30 on day one. See where you land and try to beat it next week.
2. Swap in whole grains that aren't wheat
Buckwheat (not actually wheat), quinoa, brown rice and wild rice all fit this week, and each is another plant on your tally. Skip oats this week. Products containing oats can't be labelled gluten free in Australia (Coeliac Australia, oats).
3. Add one legume a day
Lentils, chickpeas, cannellini and black beans are rich in fibre, and tinned ones count. Add a few tablespoons to a salad, soup or your Sunday cook-up, and build from there.
4. Sprinkle seeds and nuts
A tablespoon of chia, ground flaxseed, pumpkin or sunflower seeds on yoghurt, salads or vegetables adds fibre and two or three plants to your tally in one go.
5. Make your cook-up rice work twice
One easy example: when rice or potatoes are cooked and then chilled, some of the starch changes into resistant starch, the kind your bacteria can ferment. In one small study, white rice chilled overnight in the fridge and then reheated had more than twice the resistant starch of freshly cooked rice, and gave a lower blood-sugar response (Sonia et al., 2015). If you cook rice on Sunday, chilling it for the week is a neat bonus. Cool it quickly and keep it refrigerated.
6. Add a ferment, and read the label
Sauerkraut, kimchi, plain kefir, plain natural yoghurt, miso and tempeh all fit. Look for fridge-section ferments labelled "unpasteurised" or "live cultures". Then use your Week 3 label skills: some kimchi and flavoured kefirs contain added sugar, and regular soy sauce contains wheat (tamari is usually gluten free, but check). Kombucha is brewed with sugar, some of which stays in the bottle, and many contain juice, so leave it out this week.
If you're in perimenopause or menopause
Your gut bacteria and your hormones interact. Some gut bacteria make enzymes that can reactivate oestrogen so it's reabsorbed, a set of genes researchers call the "estrobolome".
In a study of 2,300 Hispanic and Latino adults in the US, postmenopausal women tended to have less diverse gut bacteria than premenopausal women, and their mix looked a little more like men's. Some of those differences were linked with less favourable heart and metabolic markers (Peters et al., 2022). This was observational, in one population, and a review by the same team says much more research is needed (Peters et al., 2022, review). We don't yet know whether diet changes this pattern.
What we do know is that heart and metabolic risk rises after menopause, and fibre is one of the best-studied ways to support both. This week's habits are worth keeping long after Friday. And if your bowel habits have changed recently, or you have bleeding, pain or unexplained weight change, see your GP rather than putting it down to hormones.
What this article isn't saying
- That gluten, coffee or alcohol are toxic. They come back next week, and many people do well with them.
- That you need to hit exactly 30 plants. It's a nudge toward variety, not a pass mark.
- That a few spoonfuls of kimchi will lower your inflammation. One small trial found a link worth exploring, not a treatment.
- That everyone should eat more fibre right away. If you have IBS or another gut condition, get advice first.
Common questions
Should I take a probiotic supplement instead?
The Stanford trial used everyday fermented foods, not capsules, so it doesn't tell us about supplements. If you're considering a probiotic for a specific condition, ask your GP or pharmacist.
I have IBS. Should I do this week?
You can follow the gluten, coffee and alcohol part as written. Go slower with the extra fibre and ferments, and talk to your GP or a dietitian about which fibre sources suit you, especially if you're on a low-FODMAP plan.
About this article
Written by the I Quit Sugar team for the 8-Week Program, and reviewed against the peer-reviewed sources listed below.
Not medical advice. This article is general education. It isn't a diagnosis or a substitute for advice from your own health professional. If you're managing a medical condition, are pregnant or breastfeeding, or take medication, speak with your doctor before making significant changes to how you eat.
References
- Topping DL, Clifton PM. Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides. Physiol Rev. 2001;81(3):1031–64. DOI
- National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand: Dietary fibre. NHMRC
- Fayet-Moore F, Cassettari T, Tuck K, McConnell A, Petocz P. Dietary fibre intake in Australia. Paper I: Associations with demographic, socio-economic, and anthropometric factors. Nutrients. 2018;10(5):599. DOI
- Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. 2019;393(10170):434–445. DOI
- McDonald D, Hyde E, Debelius JW, et al. American Gut: an open platform for citizen science microbiome research. mSystems. 2018;3(3):e00031-18. DOI
- Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137–4153.e14. DOI
- Coeliac Australia. Diagnosis. Coeliac Australia
- Coeliac Australia. Oats: commonly asked questions. Coeliac Australia
- Juliano LM, Griffiths RR. A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features. Psychopharmacology. 2004;176(1):1–29. DOI
- Sonia S, Witjaksono F, Ridwan R. Effect of cooling of cooked white rice on resistant starch content and glycemic response. Asia Pac J Clin Nutr. 2015;24(4):620–5. DOI
- Peters BA, Lin J, Qi Q, et al. Menopause is associated with an altered gut microbiome and estrobolome, with implications for adverse cardiometabolic risk in the Hispanic Community Health Study/Study of Latinos. mSystems. 2022;7(3):e0027322. DOI
- Peters BA, Santoro N, Kaplan RC, Qi Q. Spotlight on the gut microbiome in menopause: current insights. Int J Womens Health. 2022;14:1059–1072. DOI
