Written by Dr Zeeshan Afzal (MBBS) — Medical Doctor & Medical Content Lead, Welzo
Medically reviewed for accuracy · Evidence-based · Grounded in peer-reviewed research
Last updated: January 2026 · Reading time: ~12 minutes
Short-chain fatty acids (SCFAs) are among the most important molecules your gut bacteria make — and one of the clearest reasons fibre matters so much to digestive health. They are also the mechanism behind many gut health supplements, yet most people have never heard of them. When the microbes in your large intestine ferment the fibre you eat, they release these small but powerful compounds, chiefly acetate, propionate and butyrate. Far from being waste, SCFAs fuel your gut lining, calm inflammation, help regulate blood sugar and cholesterol, and even send signals to your brain.
In this guide I'll explain what short-chain fatty acids are, how the three main types differ, why the balance between them matters, and the practical, evidence-based ways to produce more of them through diet. Understanding SCFAs is one of the clearest windows into why fibre and plant diversity matter so much for health.
The short version: Acetate, propionate and butyrate are produced by gut bacteria fermenting dietary fibre, typically in a rough 60:20:20 ratio. Butyrate is the main fuel for your colon cells and supports the gut lining; propionate acts on the liver to influence glucose and cholesterol; acetate is the most abundant and travels around the body. The best way to boost them is more fibre and a wider variety of plants. Explore Welzo's gut health range for prebiotic and fibre support.
Table of contents
Short-chain fatty acids are organic acids with fewer than six carbon atoms, produced when gut bacteria ferment carbohydrates that your own digestive enzymes can't break down. The three dominant SCFAs — acetate (2 carbons), propionate (3 carbons) and butyrate (4 carbons) — make up at least 95% of the SCFAs in your colon (Den Besten et al., Journal of Lipid Research, 2013).
The process is called anaerobic fermentation. When fibre and resistant starch escape digestion in the small intestine, they reach the colon, where trillions of bacteria ferment them for energy — releasing SCFAs as a beneficial by-product. This is the core reason dietary fibre is so valuable: it's not just "roughage," it's food for the microbes that in turn nourish you. It's also why a diverse, fibre-rich diet supports a healthy gut barrier.
SCFA concentrations are highest in the first part of the colon, where fermentable material is most abundant, ranging from roughly 70–140 mM in the proximal colon down to 20–70 mM further along (Parada Venegas et al., Frontiers in Immunology, 2019).
In a healthy colon, acetate, propionate and butyrate occur in an approximate molar ratio of 60:20:20 — a figure first established decades ago and repeatedly confirmed since (review, 2021). This isn't just a curiosity: the ratio reflects a balanced microbial ecosystem, and each of the three SCFAs has distinct jobs, which we'll unpack next.
Although they're often grouped together, acetate, propionate and butyrate behave quite differently once absorbed. Here's how they compare:
| SCFA | Approx. share | Where it acts | Main roles |
|---|---|---|---|
| Acetate (C2) | ~60% | Liver & whole body | Most abundant; enters circulation; used in fat and energy metabolism; signals to the brain and appetite centres. |
| Propionate (C3) | ~20% | Mainly liver | Largely taken up by the liver; involved in glucose production and cholesterol regulation. |
| Butyrate (C4) | ~20% | Colon lining | Primary fuel for colon cells (~70% of their energy); supports the gut barrier and has anti-inflammatory effects. |
Sources: Den Besten et al., J Lipid Res (2013); Parada Venegas et al., Front Immunol (2019).
If SCFAs have a superstar, it's butyrate. Though it makes up only about a fifth of your SCFAs, it's the one the cells lining your colon rely on most.
Colon-lining cells (colonocytes) derive roughly 60–70% of their energy from SCFAs, and they preferentially burn butyrate (Den Besten et al., 2013). By keeping these cells well fuelled, butyrate helps maintain the tight-junction proteins that seal the gut lining — one reason low butyrate is linked with a weakened barrier. If you'd like the deeper mechanics, see our guide to gut barrier function.
Butyrate is also a signalling molecule. It acts on receptors (such as GPR109a) and inhibits enzymes called histone deacetylases, which together help train the immune system — for example, by encouraging the development of regulatory T cells that keep inflammation in check (Parada Venegas et al., 2019). Reduced levels of butyrate-producing bacteria such as Faecalibacterium prausnitzii and Roseburia are a recognised feature of inflammatory bowel disease, though this is an association rather than proof of cause.
Acetate is the smallest and most plentiful short-chain fatty acid, typically making up around 60% of the total. Unlike butyrate, much of it isn't used up in the gut — it's absorbed and travels through the bloodstream to tissues around the body, where it can be used as an energy substrate and in fat metabolism.
Acetate also appears to play a role in appetite signalling and communication with the brain, part of the wider gut–body conversation. Because it's produced by a broad range of bacteria, acetate is usually the SCFA that rises most readily when you increase your fibre intake.
Propionate is the three-carbon SCFA, and it has a particularly close relationship with the liver. After it's absorbed, the liver takes up most of it and uses it as a building block for glucose production (gluconeogenesis), while also influencing cholesterol metabolism (Chambers et al., 2014).
This is one of the mechanisms thought to underlie fibre's benefits for blood sugar balance and heart health. Certain fermentable fibres that boost propionate are being studied for their effects on appetite and metabolism — a reminder that the type of fibre you eat, not just the amount, shapes which SCFAs you make.
Bringing the three together, short-chain fatty acids influence health on several fronts:
It's worth keeping expectations realistic: much of the most striking data comes from laboratory and animal studies, and human evidence — while promising — is still developing. The consistent, practical takeaway is that a diet which produces plenty of SCFAs is a diet rich in fibre and plants, which is beneficial for many other reasons too.
You don't need a supplement to raise your SCFAs — you need to feed the bacteria that make them. Here's how, in order of impact.
Different fibres feed different bacteria and yield different SCFAs, so variety is key. The UK fibre target is 30g a day, and most people fall well short. Build up gradually to avoid bloating, and prioritise a broad range of high-fibre foods — vegetables, wholegrains, pulses, nuts, seeds and fruit.
Resistant starch is a particularly good butyrate promoter. It's found in cooked-and-cooled potatoes, rice and pasta, slightly green bananas, oats and legumes. Learn more in our guide to resistant starch.
Prebiotic fibres such as inulin and modified citrus pectin are readily fermented into SCFAs — see our overview of the best prebiotic supplements. Some people also use butyrate supplements directly, though feeding your own bacteria is generally the more sustainable approach. A diverse microbiome helps too, which is where probiotics and mucus-supporting species like Akkermansia may play a supporting role.
Welzo's wider gut range also includes options studied for metabolic and bile-related support, such as berberine and TUDCA; these target different pathways and aren't SCFA boosters, so choose based on your specific goal and seek guidance if unsure.
SCFAs are part of everyday healthy digestion, not something most people need to test or treat. But digestive symptoms should never be ignored when they're persistent or severe.
See your GP promptly if you have:
These need proper assessment. Source: NHS — Symptoms of bowel cancer.
Short-chain fatty acids are organic acids with fewer than six carbons, produced when gut bacteria ferment dietary fibre in the colon. The three main ones are acetate, propionate and butyrate, which together make up over 95% of the SCFAs in the gut. They fuel gut cells, regulate immunity and influence metabolism.
Acetate is the most abundant, making up around 60% of colonic SCFAs, followed by propionate and butyrate at roughly 20% each — the classic 60:20:20 ratio. However, butyrate is often considered the most physiologically important because it's the primary fuel for the cells lining the colon.
Butyrate is the main energy source for colon-lining cells, providing around 70% of their fuel, and it helps maintain the gut barrier. It also acts as a signalling molecule with anti-inflammatory effects, supporting immune balance in the gut.
They differ in size and destination. Acetate (2 carbons) is most abundant and circulates around the body; propionate (3 carbons) is mainly taken up by the liver and influences glucose and cholesterol; butyrate (4 carbons) is used locally by colon cells as fuel and supports the gut lining and immune system.
High-fibre and fermentable foods do: vegetables, wholegrains, pulses, nuts, seeds and fruit, plus resistant-starch foods like cooked-and-cooled potatoes, rice and oats, and slightly green bananas. Variety matters, because different fibres feed different SCFA-producing bacteria.
It's the approximate molar ratio of acetate to propionate to butyrate found in a healthy colon. This balance reflects a well-functioning microbial ecosystem, though exact proportions vary with diet, gut region and the individual.
Direct butyrate supplements exist and some people use them, but for most people, feeding your own bacteria with a varied, fibre-rich diet is the more sustainable way to raise SCFAs. Supplements may have a role in specific situations; if you have a medical condition, seek professional guidance first.
SCFAs, especially butyrate, promote anti-inflammatory immune responses — for example by encouraging regulatory T cells that keep inflammation in check. Low SCFA levels are associated with inflammatory conditions such as inflammatory bowel disease, though this is a correlation rather than proof of cause.
Some probiotic strains can support SCFA production, and a more diverse microbiome is generally better at fermenting fibre. However, the biggest driver of SCFA production is the amount and variety of fermentable fibre you eat, so diet comes first.
Gut bacteria respond to dietary changes within days, and SCFA production can rise quickly when you increase fibre. However, stable, lasting shifts in your microbiome and its output usually build over several weeks of consistent eating rather than overnight.
Medical disclaimer: This article is for general information and education only and does not constitute medical advice, diagnosis or treatment. It should not replace consultation with a qualified healthcare professional. Always seek the advice of your GP or a suitably qualified clinician about any symptoms or before starting new supplements, particularly if you are pregnant, breastfeeding, immunocompromised or taking medication. If you have red-flag symptoms, seek medical care promptly.
About the author
Dr Zeeshan Afzal (MBBS) is a practising medical doctor and Welzo's Medical Content Lead. He writes and reviews Welzo's health content to ensure it is accurate, evidence-based and aligned with current UK clinical guidance, translating complex research into practical advice patients can trust.
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