Gut bacteria
Postbiotics explained: short-chain fatty acids and gut health
Postbiotics are preparations of non-living microbes, or parts of them, that provide a health benefit. The word is also used loosely for the useful substances that gut bacteria make, especially short-chain fatty acids such as butyrate. These acids fuel the cells lining the colon and help to control inflammation. The most reliable way to increase them is to eat more fibre. Evidence for postbiotic supplements is still at an early stage.
In short
- Probiotics are live microbes. Postbiotics are not alive.
- Short-chain fatty acids are made when gut bacteria ferment fibre. Strictly, they are microbial products and not postbiotics, though the terms are often mixed.
- Butyrate is the main fuel of the colon’s lining.
- Fibre from a variety of plants raises short-chain fatty acids. Supplements have limited evidence so far.
What exactly is a postbiotic?
An international expert panel defined a postbiotic in 2021 as a preparation of inanimate microorganisms, or their components, that confers a health benefit. In practice this means bacteria that have been deliberately inactivated, usually by heat, with or without the substances they produced.
Purified substances made by bacteria, such as butyrate on its own, fall outside this definition. Popular articles often call them postbiotics anyway. This guide covers both.
| What it is | Alive? | |
|---|---|---|
| Prebiotic | Fibre that feeds beneficial bacteria | Not applicable |
| Probiotic | Beneficial bacteria or yeast | Yes |
| Postbiotic | Inactivated microbes or their parts | No |
| Microbial products | Substances bacteria make, such as short-chain fatty acids | Not applicable |
What are short-chain fatty acids?
When fibre reaches the colon, bacteria ferment it and release three main acids: acetate, propionate and butyrate.
They feed the colon
Butyrate supplies most of the energy used by the cells that line the colon.
They support the gut barrier
They help to maintain the mucus layer and the seals between cells. See the gut lining.
They calm immune activity
They encourage the immune cells that restrain inflammation.
They signal to the rest of the body
They act on cells in the gut wall that release hormones involved in appetite and blood sugar control.
Much of this knowledge comes from laboratory and animal research. In people, the consistent finding is that diets rich in fibre are linked with better long-term health.
How do I increase them?
Eat a variety of fibre
Vegetables, fruit, pulses, whole grains and millets. Different fibres feed different bacteria. See fibre.
Include resistant starch
Starch that escapes digestion and is fermented in the colon. Sources include pulses, slightly unripe bananas, and rice or potatoes that have been cooked and then cooled.
Add fermented foods
Curd, buttermilk and other traditional ferments.
Protect your gut bacteria
Use antibiotics only when needed.
Do postbiotic supplements work?
Heat-inactivated bacteria
A small number of trials have shown benefit in specific settings, including one in irritable bowel syndrome. The results need to be repeated.
Butyrate supplements
Much of an oral dose is absorbed before it reaches the colon. Human studies are few and small.
Possible advantages
Because they contain no live organisms, postbiotics are stable in heat and carry no risk of infection, which may matter for people with weak immunity.
At present there is not enough evidence to recommend a postbiotic supplement for general gut health. This is a field worth watching.
When should I see a doctor?
Persistent bloating, loose stools, bleeding or weight loss need a diagnosis, not a supplement. See conditions I treat.
Questions patients ask me
Are postbiotics better than probiotics?
They are different, not better. Probiotics have more research behind them. Postbiotics are more stable and may suit people who should avoid live organisms. For both, the benefit depends on the specific product and condition.
Can I get butyrate from food?
Small amounts are present in ghee and butter. Far more is made in your own colon when bacteria ferment fibre, which is why fibre matters more than any direct source.
Does cooked and cooled rice really help?
Cooling cooked rice or potato converts some of its starch into resistant starch, which feeds gut bacteria. The effect is modest and is one small part of a fibre-rich diet.
Should I take a butyrate supplement?
Not routinely. If you have a specific bowel condition, discuss it with your doctor. For most people, increasing fibre is the effective route.
Sources
This page is written for patients and is based on the guidelines and studies below. It is for education and does not replace a consultation.
- International consensus statement on the definition of postbiotics. Salminen S et al. Nat Rev Gastroenterol Hepatol. 2021. PubMed 33948025
- International consensus statement on the definition of prebiotics. Gibson GR et al. Nat Rev Gastroenterol Hepatol. 2017. PubMed 28611480
- Review of short-chain fatty acids as key bacterial metabolites. Koh A et al. Cell. 2016. doi:10.1016/j.cell.2016.05.041
- Systematic reviews of carbohydrate quality and human health. Reynolds A et al. Lancet. 2019. PubMed 30638909
- Review of intestinal permeability: mechanisms, measurement and clinical implications. Camilleri M. Gut. 2019. PubMed 31076401