Does Gut Health Affect Your Skin? What PHGG Fibre Can Do

Yes, gut health and skin are linked, and prebiotic fibre is one of the more plausible ways to influence that link. In a placebo-controlled trial in 2025, adults who took 5 g a day of partially hydrolysed guar gum (PHGG) over a winter had better skin elasticity after 12 weeks, and lower water loss from the cheek after 6 weeks, than the placebo group. Skin moisture rose in both groups, and no study has tested PHGG for acne.

“Gut-skin” has become one of the busiest ideas in Australian wellness marketing, from 90-day acne programs to beauty powders promising a glow from within. The research behind it is real but narrower than the marketing, so this post sticks to what has been measured: how gut bacteria can affect skin, what the PHGG trials found, how fibre compares with other dietary approaches, and what Australian food law lets a fibre product say.

What is the gut-skin axis?

The gut-skin axis is the two-way communication between the gut and the skin. It runs mainly through three channels: the immune system, compounds made by gut bacteria that are absorbed into the blood, and the gut barrier, which controls how much of those compounds reach the circulation.¹ Reviews of the axis link gut microbiome changes with several inflammatory skin conditions, although most of that evidence shows association rather than cause.¹

Most skin research measures three things: hydration, which is how much water the outer layer of skin holds; water loss, which is how quickly water evaporates through the skin (lower means a stronger skin barrier); and elasticity, which is how well skin springs back after being stretched. These are the outcomes reported in the studies below.²

How can fibre in your gut affect your skin?

When gut bacteria ferment fibres such as PHGG, they produce short-chain fatty acids (SCFAs), mainly butyrate, propionate and acetate, and some of these are absorbed into the bloodstream and reach the skin.³ In one animal study, it was found that those gut-derived SCFAs increase metabolism in keratinocytes (the main cells of your outer skin) and drive the differentiation process that builds the skin’s protective outer layer, producing a stronger skin barrier.⁴ How fibre produces SCFAs, and what they do in the gut, is covered in our article on fibre and inflammation.

The second route is related to reducing protein fermentation in the gut by providing an alternative fuel and lowering the pH of the colon. Some protein always escapes digestion, and more of it does on a very high-protein diet. That leftover protein reaches the colon, where bacteria break it down into compounds such as phenol and p-cresol, which reach the skin through our bloodstream and affect how new skin cells mature.^5,6 So eating more protein than you need may affect your skin as well as your gut. Our post on protein farts explains the same fermentation shift from the gut’s side, if you are interested in reading more about it.

Research by Miyazaki and colleagues found that fermented milk containing both pre- and probiotics reduced blood phenol levels and helped prevent skin dryness in healthy women.⁶ That is relevant to the gut-skin hypothesis, although the combined intervention cannot tell us whether prebiotic fibre alone would have the same effect.

What did the PHGG skin studies find?

Two human trials have tested PHGG on skin, both run in Tokyo by Taiyo Kagaku, the Japanese company that makes Sunfiber PHGG. Because both were funded by the manufacturer and most authors were company employees, the findings need independent replication before they can be treated as settled, and no such replication has been published yet. The table below summarises the two trials.

In the first study, the main finding was that daily PHGG at either dose helped prevent the drop in skin moisture as winter grew colder and drier.⁷ Skin moisture also improved in the 2025 trial, but it improved in the placebo group too, so the difference between the groups was not statistically significant. That trial measured more parameters, though, and found that skin elasticity improved after 12 weeks of PHGG, and skin brightness after 6 weeks, compared with placebo.²

Can other prebiotic fibres improve skin?

Because research on PHGG and skin is still at an early stage, it helps to look at prebiotic fibre as a whole. Prebiotics are fibres that feed beneficial gut bacteria, and recent reviews of the gut-skin axis describe them as a promising way to support skin hydration and the skin barrier.^8,9

Three placebo-controlled human trials have tested other prebiotic fibres on skin.^10–12 Over 4 to 12 weeks, they found improvements in skin hydration, wrinkle area, depth and severity, and protection against drying of the skin’s outer layer. The trials were small and mostly in Korean and Japanese adults, but alongside the PHGG studies, they add up to evidence that prebiotics as a whole could help support skin health.

A 2025 meta-analysis of dietary interventions for skin ageing from the National University of Singapore pooled 61 human studies. Although it grouped prebiotics and probiotics together as one category, likely because so few studies have investigated prebiotics on their own, it found that the category significantly improved skin hydration.¹³

All in all, functional foods are foods, not medicines, so their effects tend to be smaller and slower to show, which makes them hard to detect in a trial of a few dozen people over 12 weeks. A non-significant result means a study could not separate an effect from chance, not that the fibre did nothing, and small benefits to hydration and barrier function could add up over months of daily intake, although no larger or longer trial has tested that yet.

Should you take fibre for your skin?

Yes, fibre could benefit your skin, as long as you go in with realistic expectations. The best current evidence points to modest improvements in skin elasticity and water loss after 6 to 12 weeks of daily PHGG during dry weather: small, gradual support rather than a transformation. Don’t expect drastic changes, and don’t expect fibre to solve a skin problem such as acne, eczema or rosacea.

As a nutritionist, I am often asked for my opinion on supplements, and my professional judgement is always the same: if a supplement poses no safety concern and might help, it can be worth giving it a go, because everyone’s body is different. Fibre fits that description well, because even if it turns out to do little for your skin, it is worth getting right for other reasons. Our blog, The Fibre Lab, covers the different benefits of fibre in detail, from easing constipation and managing bloating to its links with inflammation, mood and menopause.

All in all, food is still the foundation. If you add a supplement, we have written guides that compare different popular fibre option and review the different fibre formats available. PuriFibre, on the other hand, is a liquid prebiotic fibre shot made with PHGG in combination with other traditional gut-benefiting ingredients, developed by two PhDs in Western Australia. It is low-FODMAP and gluten-free, designed for people who find powders and capsules hard to stick with and want an easier way to reach their daily fibre intake.

The takeaway

Looking after your gut may benefit your skin as well. The evidence from human trials is still thin, but researchers have identified several ways it could work, and two of the most likely are SCFAs that support the skin barrier and less protein fermentation producing the phenols that disturb it. That said, around 80% of Australians do not get enough fibre, the risk of trying is low, and fibre does so much good elsewhere in the body, so it may well be worth a try, and PHGG is a good place to start.

Important note

This article is general information, not medical advice. Acne, eczema, rosacea, persistent itch, or skin that is dry, cracked or changing despite good skincare should be assessed by a GP or dermatologist. If you have a gut condition, take medication, or are pregnant, check with your healthcare professional before starting a new fibre product.

References

1. Salem, I.; Ramser, A.; Isham, N.; Ghannoum, M. A. The Gut Microbiome as a Major Regulator of the Gut-Skin Axis. Front. Microbiol. 2018, 9, 1459. https://doi.org/10.3389/fmicb.2018.01459
2. Kapoor, M. P.; Abe, A.; Morishima, S.; Nakajima, A.; Ozeki, M.; Sato, N. Dietary Intervention of Prebiotic Partially Hydrolyzed Guar Gum Improves Skin Viscoelasticity, Stratum Corneum Hydration, and Reduction of Trans-Epidermal Water Loss: A Randomized, Double-Blind, and Placebo-Controlled Clinical Study in Healthy Humans. J. Clin. Biochem. Nutr. 2025, 76 (1), 96–115. https://doi.org/10.3164/jcbn.24-69
3. Ohashi, Y.; Sumitani, K.; Tokunaga, M.; Ishihara, N.; Okubo, T.; Fujisawa, T. Consumption of Partially Hydrolysed Guar Gum Stimulates Bifidobacteria and Butyrate-Producing Bacteria in the Human Large Intestine. Benef. Microbes 2015, 6 (4), 451–455. https://doi.org/10.3920/BM2014.0118
4. Trompette, A.; Pernot, J.; Perdijk, O.; Alqahtani, R. A. A.; Domingo, J. S.; Camacho-Muñoz, D.; et al. Gut-Derived Short-Chain Fatty Acids Modulate Skin Barrier Integrity by Promoting Keratinocyte Metabolism and Differentiation. Mucosal Immunol. 2022, 15, 908–926. https://doi.org/10.1038/s41385-022-00524-9
5. Iizuka, R.; Kawakami, K.; Chiba, K. Gut Bacteria Producing Phenols Disturb Keratinocyte Differentiation in Human Skin. Microb. Ecol. Health Dis. 2009, 21 (3–4), 221–227. [REPLACE-DOI]
6. Miyazaki, K.; Masuoka, N.; Kano, M.; Iizuka, R. Bifidobacterium Fermented Milk and Galacto-Oligosaccharides Lead to Improved Skin Health by Decreasing Phenols Production by Gut Microbiota. Benef. Microbes 2014, 5 (2), 121–128. https://doi.org/10.3920/BM2012.0066
7. Kapoor, M. P.; Yamaguchi, H.; Ishida, H.; Mizutani, Y.; Timm, D.; Abe, A. The Effects of Prebiotic Partially Hydrolyzed Guar Gum on Skin Hydration: A Randomized, Open-Label, Parallel, Controlled Study in Healthy Humans. J. Funct. Foods 2023, 103, 105494. https://doi.org/10.1016/j.jff.2023.105494
8. Woo, Y. R.; Kim, H. S. Interaction between the Microbiota and the Skin Barrier in Aging Skin: A Comprehensive Review. Front. Physiol. 2024, 15, 1322205. https://doi.org/10.3389/fphys.2024.1322205
9. Lolou, V.; Panayiotidis, M. I. Functional Role of Probiotics and Prebiotics on Skin Health and Disease. Fermentation 2019, 5 (2), 41. https://doi.org/10.3390/fermentation5020041
10. Hong, Y. H.; Chang, U. J.; Kim, Y. S.; Jung, E. Y.; Suh, H. J. Dietary Galacto-Oligosaccharides Improve Skin Health: A Randomized Double Blind Clinical Trial. Asia Pac. J. Clin. Nutr. 2017, 26 (4), 613–618. https://doi.org/10.6133/apjcn.052016.05
11. Jung, E. Y.; Kwon, J. I.; Hong, Y. H.; Suh, H. J. Evaluation of Anti-Wrinkle Effects of Duoligo, Composed of Lactulose and Galactooligosaccharides. Prev. Nutr. Food Sci. 2017, 22 (4), 381–384. https://doi.org/10.3746/pnf.2017.22.4.381
12. Kano, M.; Masuoka, N.; Kaga, C.; Sugimoto, S.; Iizuka, R.; Manabe, K.; et al. Consecutive Intake of Fermented Milk Containing Bifidobacterium breve Strain Yakult and Galacto-Oligosaccharides Benefits Skin Condition in Healthy Adult Women. Biosci. Microbiota Food Health 2013, 32 (1), 33–39. https://doi.org/10.12938/bmfh.32.33
13. Ng, J. Y.; Ng, X. M. G. Y.; Wong, Q. Y. A.; Chew, F. T. Dietary Interventions in Skin Ageing: A Systematic Review and Meta-Analysis. J. Physiol. Anthropol. 2025, 44, 26. https://doi.org/10.1186/s40101-025-00408-4