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03. The Gut Microbiome and GLP‑1 — The Role of Fibre and Short-Chain Fatty Acids
Gut microorganisms do more than process food residues. They also produce substances that scientists study as part of communication between the gut and the rest of the body.
These substances include short-chain fatty acids, known as SCFAs. How do they arise from fibre, and what do we know about their relationship with GLP‑1, satiety and weight regulation?
What is the gut microbiome?
The term gut microbiota refers to the community of microorganisms living in the intestine. Microbiome is also used in a broader sense that includes their genetic material and environment. In everyday communication, these terms are often used interchangeably.
Their activity is central to this topic: certain gut bacteria can ferment food components that our digestive enzymes do not fully break down. Processing fermentable fibre produces SCFAs, among other substances. [1, 2]
From fibre to metabolites
1. Fibre
Some fibre reaches the colon, where it becomes available for microbial processing.
2. Fermentation
Microorganisms use suitable substrates and convert them into various metabolites.
3. SCFAs
The products include acetate, propionate and butyrate, which are also studied in relation to gut hormones.
This sequence describes a biological process. It does not mean that every type of fibre or every serving of food produces the same hormonal response. Nor can findings from an experiment with a specific substance automatically be attributed to an entire food group.
What does SCFA stand for?
SCFA stands for short-chain fatty acids. The following three substances are among the most frequently studied:
| Substance | Chemical description | Relevance to this topic |
|---|---|---|
| Acetate | A salt or the ionised form of acetic acid. | One of the main products of gut fermentation; also studied in metabolic experiments. |
| Propionate | A salt or the ionised form of propionic acid. | Studied in research on targeted delivery to the colon and the subsequent hormonal response. |
| Butyrate | A salt or the ionised form of butyric acid. | Another fermentation product, studied individually and in SCFA mixtures. |
How might SCFAs relate to GLP‑1?
One mechanism under investigation is the action of SCFAs on receptors in intestinal cells. In work by Tolhurst and colleagues, researchers observed GLP‑1 release after exposing cell cultures to SCFAs. They also investigated the receptors FFAR2 and FFAR3 and mice lacking one of these receptors. [1]
The results support a biological link between gut bacterial metabolites and GLP‑1 secretion. However, this was preclinical research, rather than evidence that a particular food or supplement reduces hunger in humans.
A receptor does not guarantee an outcome. A substance activating a signalling pathway in an experiment does not, by itself, establish the strength, duration or practical significance of its effect in the human body.
What has research found in humans?
Targeted delivery of propionate
Chambers and colleagues developed an inulin–propionate ester that delivered propionate to the colon. In the short-term part of the research, they observed increased GLP‑1 and PYY and lower energy intake. In a 24-week study involving 60 adults with overweight, they observed less weight gain than in the control group. [2]
However, the ester studied is not identical to ordinary inulin or dietary fibre. The result therefore does not establish a universal effect of all fibre preparations.
Not every study found an increase in GLP‑1
In another randomised experiment, 12 men with overweight or obesity received SCFA mixtures directly into the colon. Researchers observed changes in some metabolic measures and an increase in PYY. However, they found no significant difference in GLP‑1 between the mixtures tested and placebo. [3]
This finding matters too. It shows that the response is not automatic. Furthermore, delivering substances directly into the intestine differs from everyday eating, and a short-term experiment does not establish long-term weight loss.
What does this mean for food choices?
It makes sense to view fibre as part of overall nutrition, rather than solely as a tool for influencing one hormone. WHO recommends that adults consume at least 25 grams of naturally occurring dietary fibre daily. Recommended sources include whole grains, vegetables, fruit and pulses. [4]
In practice, this could mean varying oats, lentils, chickpeas, wholegrain side dishes, vegetables and fruit. However, these examples do not constitute a ranking of the ‘strongest GLP‑1 stimulators’.
If you have a digestive condition or a prescribed diet, the suitable type and amount of fibre may differ from general recommendations.
How can you recognise an overstated promise?
When encountering headlines such as ‘feed your bacteria and switch off hunger’, ask three questions: did the researchers study humans? Did they use the same food or preparation? Did they also measure actual food intake and long-term body weight?
A change in the microbiome, an increased metabolite concentration and a clinical benefit are different outcomes. Similarly, without specific evidence, we cannot assume that every probiotic or prebiotic preparation increases GLP‑1.
Frequently asked questions
Are SCFAs hormones?
No. They are short-chain fatty acids. They can participate in signalling within the body, and their relationship with the release of hormones such as GLP‑1 is being investigated. [1]
Does every type of fibre increase GLP‑1?
The studies described do not support such a general conclusion. Research on a specific ester or a directly administered SCFA mixture cannot be applied to all types of fibre. [2, 3]
Is inulin the same as inulin–propionate ester?
No. The cited study used a specially prepared compound designed to deliver propionate to the colon. Its findings cannot automatically be attributed to ordinary inulin. [2]
Does this research demonstrate weight loss from probiotics?
No. The studies described do not establish a weight-loss effect for any arbitrary probiotic. Each specific preparation and outcome would need to be tested separately.
Why did some experiments find no increase in GLP‑1?
Studies differ in the substances, doses, sites and methods of administration, and participants. Their differing results remind us that a simple explanation of a mechanism may not predict the response in every experiment. [1–3]
Simply put
Fibre fermentation, gut metabolites and GLP‑1 form an interesting field of research. However, the available experiments do not support a universal promise that a particular fibre or microbiome change will reliably eliminate hunger and reduce body weight.
Next article, 04: Berberine and GLP‑1 — what studies show and what we still do not know.
Continue to article 04: Berberine and GLP-1 →Curious about what’s in food supplements?
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Educational purpose: This article does not replace individual medical assessment, diagnosis or treatment. It does not recommend changing prescribed treatment or deliberately influencing hormones with supplements.
