Fibre types compared: how fermentation powers fibremaxxing

Your feed says "fibremaxxing". Your nani says "isabgol at night". Your gym friend swears by a mystery prebiotic powder. All three are talking about fibre, but they are not talking about the same thing.

Fibres are not interchangeable. Psyllium (isabgol) forms a gel and is barely fermented, so it mainly bulks and softens stool. Inulin ferments fast, feeding gut bacteria but causing more gas. Oat beta-glucan is viscous and lowers LDL cholesterol. PHGG ferments at a middle pace. For "fibremaxxing", variety and a slow ramp-up beat one powder.

Last updated: November 2026

The problem

"Fibremaxxing" took off on TikTok in 2025: people pushing their daily fibre to meet or exceed the recommended amount, and encouraging others to do the same (CNBC, 2025). Registered dietitian Mia Syn called it "pretty safe", with one warning: "It is possible to do too much too soon."

The trend has a point. In the US, more than 90% of women and 97% of men don't meet fibre recommendations (CNN, 2025), and a large Lancet review linked 25–29 g a day to the largest health benefits (Reynolds et al., 2019).

The catch is that "fibre" is a family, not a single ingredient. A spoon of isabgol and a spoon of inulin behave like cousins who share a surname and nothing else. Which one you add changes what happens in your gut, and how your evening goes.

Why it happens

Three properties decide what a fibre does

Dietary fibre is carbohydrate that is neither digested nor absorbed in the small intestine (Holscher, 2017). After that, three questions matter:

1. Does it dissolve? Soluble fibres dissolve in water; insoluble ones, like wheat bran and cellulose, don't.
2. Does it gel? Viscous, gel-forming fibres such as beta-glucan, psyllium and raw guar gum slow things down in the small intestine. That viscosity is what lowers cholesterol; insoluble wheat bran doesn't do this (McRorie & McKeown, 2017).
3. Do bacteria ferment it? Fermentable fibres become food for gut microbes in the colon. Non-fermented fibres stay intact and hold water.

Fermentation, step by step

Fermentation is the part fibremaxxing videos rarely explain. Here is what happens to a fermentable fibre, like the beta-glucan in your oats or the resistant starch in cooled rice.

Butyrate is the colon's favourite fuel. It is the key energy source for the cells lining your colon (Holscher, 2017).

Short-chain fatty acids talk to your hormones. In people, infusing acetate raised blood levels of PYY and GLP-1, the gut hormones that help with fullness and insulin release (Koh et al., 2016). In a trial of 60 overweight adults, 10 g of a propionate-releasing inulin compound raised post-meal PYY and GLP-1 and, over 24 weeks, reduced weight gain (Chambers et al., 2015). The receptor details come mostly from mouse studies, and their role in humans "needs to be clarified" (Koh et al., 2016).

Gas is part of the deal. Microbial fermentation is the body's only source of hydrogen, which is why breath hydrogen is used to measure it (Holscher, 2017).

Fast vs slow fermenters

Speed changes comfort. In a lab fermentation study, inulin produced the most gas by 8 hours; PHGG fermented at an intermediate rate and wheat dextrin was slowest (Noack et al., 2013). That is a lab model, not your gut, but it matches what people report.

In a crossover trial of 26 healthy adults, flatulence was the most common symptom with inulin-type fibres. Up to 10 g a day of native inulin was well tolerated, but 10 g of shorter-chain oligofructose substantially increased symptoms (Bonnema et al., 2010).

Why psyllium works differently

Psyllium is a nonfermentable fibre (Holscher, 2017). Its laxative effect comes from a water-holding gel that resists drying out, keeping stool soft and bulky. Readily fermented fibres such as inulin and FOS lose that water-holding capacity and don't provide a laxative effect (McRorie & McKeown, 2017).

So the trade-off is real. Fermentable fibres feed your microbes; gel-forming, non-fermented fibres do the plumbing. A good fibre plan uses both.

What to do

1. Count to 25–30 g, slowly. Add a few grams a week. Gastroenterologist Dr Kyle Staller of Massachusetts General Hospital put it plainly: going "from zero to 60" is "probably not going to go well" (CNN, 2025).
2. Diversify before you supplement. Dal and rajma, oats or jau, cooled rice in curd rice or lemon rice, a raw banana sabzi, whole fruit, vegetables. Each brings a different fibre profile. See our high-fibre Indian breakfasts.
3. Use the cool-rice trick. Cooling cooked rice for 24 hours at 4°C and reheating it raised resistant starch from 0.64 to 1.65 g per 100 g and lowered the glucose response in 15 healthy adults (Sonia et al., 2015).
4. Pick a supplement for its job. Constipation: a gel-former like psyllium. Cholesterol: oat beta-glucan, where 3 g or more a day lowered LDL by 0.25 mmol/L across 28 trials (Whitehead et al., 2014). Easy daily top-up: a non-gelling soluble fibre. One example is Trulo Sunfiber®, "a clinically studied soluble fiber made from guar beans" (PHGG) that "dissolves easily in water, beverages, and everyday foods without adding noticeable taste, texture, or thickness." It complements food fibre; it doesn't replace it.
5. Drink water. Fibre pulls water into the gut; without enough fluid it can mean more bloating, gas and constipation (CNN, 2025).
6. Be careful if you have IBS or take medicines. Fast fermenters can aggravate IBS symptoms, and fibre supplements can affect medicine timing. Ask your doctor or a registered dietitian before a big change.

Did you know? In a Stanford trial of 36 adults, 10 weeks of a high-fibre diet did not increase gut microbe diversity, while a fermented-food diet did. The researchers concluded that more fibre alone over a short period is insufficient to increase diversity (Wastyk et al., 2021). Fibremaxxing works best as a long game.

FAQ

Is fibremaxxing safe?
For most healthy adults, raising fibre towards 25–30 g a day is safe and linked to better health. Go slowly, drink water, and talk to your doctor if you have IBS, a gut condition or take regular medicines.

Which fibre is best for gut bacteria?
Fermentable fibres such as beta-glucan, inulin, resistant starch and PHGG feed gut microbes. Eating a range of them from whole foods is better than relying on one.

Is isabgol a prebiotic?
Not really. Psyllium is largely non-fermented, so it works through its gel rather than by feeding bacteria. It is still useful for stool consistency.

Why does fibre make me gassy?
Gas is a normal by-product of fermentation. Fast fermenters like inulin produce more of it early on. Ramping up slowly gives your gut time to adapt.

Save this guide, then read how much fibre you need per day, what PHGG is and how gut health shapes diabetes management.

Where to buy

• trulofoods.com
• Amazon

This article is for information, not medical advice. If you have diabetes or take medication, talk to your doctor before changing your diet.

Research & References

1. Reynolds A, et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet, 2019. — Supports: 25–29 g fibre a day linked to the largest benefits.
2. Holscher HD. Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut Microbes, 2017. — Supports: fibre definition; fermentability of beta-glucan, inulin, resistant starch, psyllium, cellulose; butyrate as colonocyte fuel; hydrogen from fermentation.
3. McRorie JW, McKeown NM. Understanding the physics of functional fibers in the gastrointestinal tract. Journal of the Academy of Nutrition and Dietetics, 2017. — Supports: viscosity and cholesterol; psyllium gel laxation; fermented fibres lack laxative effect.
4. Koh A, et al. From dietary fiber to host physiology: short-chain fatty acids as key bacterial metabolites. Cell, 2016. — Supports: acetate raises PYY and GLP-1 in humans; receptor evidence mostly from mice.
5. Chambers ES, et al. Effects of targeted delivery of propionate to the human colon on appetite regulation, body weight maintenance and adiposity in overweight adults. Gut, 2015. — Supports: propionate raised PYY and GLP-1 in 60 adults.
6. Noack J, et al. Fermentation profiles of wheat dextrin, inulin and partially hydrolyzed guar gum using an in vitro digestion pretreatment and in vitro batch fermentation system model. Nutrients, 2013. — Supports: inulin fastest gas, PHGG intermediate (lab study).
7. Bonnema AL, et al. Gastrointestinal tolerance of chicory inulin products. Journal of the American Dietetic Association, 2010. — Supports: inulin tolerance and flatulence.
8. Whitehead A, et al. Cholesterol-lowering effects of oat β-glucan: a meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition, 2014. — Supports: ≥3 g/day lowers LDL by 0.25 mmol/L.
9. Sonia S, et al. Effect of cooling of cooked white rice on resistant starch content and glycemic response. Asia Pacific Journal of Clinical Nutrition, 2015. — Supports: resistant starch and glucose response with cooled rice.
10. Wastyk HC, et al. Gut-microbiota-targeted diets modulate human immune status. Cell, 2021. — Supports: high-fibre diet alone didn't raise diversity in 10 weeks. Trend context: CNBC, 2025; CNN, 2025.