Short-chain fatty acids from gut bacteria stimulate the colon to release GLP-1, but through an energy metabolism pathway rather than the FFAR2/FFAR3 receptors that were previously assumed to be responsible.
FFAR2/FFAR3 receptors not involvedOverturning the prevailing theory — SCFAs trigger GLP-1 release through cellular energy metabolism, not through the fatty acid receptors widely assumed to be responsible
What the researchers found
Using an isolated perfused rat colon, the researchers found that luminal and especially vascular infusion of acetate and butyrate significantly increased GLP-1 secretion, with a smaller effect on PYY secretion (but only after intracellular cAMP was enhanced). Propionate had no effect on either hormone.
Critically, the study showed this effect does NOT work through the FFAR2 and FFAR3 fatty acid receptors, as widely assumed. A specific FFAR2/FFAR3 agonist (CFMB/AR420626) had no effect on GLP-1 output, and a FFAR3 antagonist didn't block the SCFA-induced response. Instead, blocking voltage-gated calcium channels (nifedipine), opening KATP channels (diazoxide), or inhibiting ATP synthesis (2,4-DNP) completely abolished the responses — indicating SCFAs are metabolized as an energy source by colonocytes, and it's this metabolic process that drives GLP-1 secretion.
Why it matters
This study challenges a widely held assumption in gut biology. Many researchers and supplement companies have promoted the idea that fiber and SCFAs boost GLP-1 through FFAR2/FFAR3 receptors. If the real mechanism is metabolic — SCFAs serving as fuel for colon cells — it changes how we think about designing dietary interventions, prebiotics, and microbiome therapies aimed at enhancing natural GLP-1 release. It also suggests that the specific type of SCFA matters: acetate and butyrate work, but propionate does not.
The numbers in context
Acetate and butyrate increase GLP-1 secretion · Propionate has no effect · FFAR2/FFAR3 receptors not involved · CFMB ~750x more potent than SCFAs at FFAR2 · Nifedipine, diazoxide, and 2,4-DNP abolished responses
How the study worked
The researchers used isolated perfused rat colons — an ex vivo preparation that preserves the colon's blood supply, nerve connections, and cellular architecture while allowing precise control over what the colon is exposed to. They infused SCFAs (acetate, propionate, butyrate) both luminally (from the gut side) and vascularly (through the blood supply) and measured GLP-1 and PYY secretion. They then used receptor-specific agonists, antagonists, ion channel blockers, and metabolic inhibitors to determine the exact mechanism driving hormone release.
Who was studied
Isolated perfused rat colons
What this study cannot tell us
This is an ex vivo rat colon study, which may not perfectly represent the intact human colon with its full complement of neural, hormonal, and immune inputs. The isolated preparation, while excellent for mechanistic studies, removes some physiological context. Results in rats may not directly translate to humans. The PYY response to SCFAs was only observed after cAMP enhancement, suggesting the baseline effect may be weaker than the GLP-1 response.
How to read the evidence
Rated 'strong' for a preclinical study because it used a well-controlled ex vivo model with multiple pharmacological tools to rigorously test and disprove the receptor hypothesis, published in a top physiology journal by a leading GLP-1 research group (Holst lab).
When this study was published
Published in 2018 in the American Journal of Physiology. This finding challenged the prevailing FFAR2/FFAR3 hypothesis and has influenced subsequent research on microbiome-GLP-1 interactions.
The bigger picture
This study connects two of the hottest areas in metabolic research: the gut microbiome and GLP-1 biology. With GLP-1 drugs like semaglutide transforming obesity treatment, there's enormous interest in whether natural GLP-1 release can be enhanced through diet and microbiome manipulation. This research suggests that fiber fermentation products can indeed boost GLP-1, but the mechanism is fundamentally different than assumed — it's about cellular energy metabolism, not receptor activation. This distinction matters for anyone trying to develop microbiome-based approaches to metabolic disease.
Questions still open
- Does the same SCFA metabolic mechanism drive GLP-1 secretion in the human colon, or do FFAR2/FFAR3 play a larger role in humans?
- Could dietary strategies that specifically increase colonic acetate and butyrate (but not propionate) production enhance natural GLP-1 release in people?
- Why does propionate have no effect on GLP-1 secretion despite being metabolized by colonocytes similarly to acetate and butyrate?
Common questions
What are short-chain fatty acids and where do they come from?
Does this mean eating fiber can naturally boost GLP-1 like taking Ozempic?
Read the original research
The impact of short-chain fatty acids on GLP-1 and PYY secretion from the isolated perfused rat colon.
American journal of physiology. Gastrointestinal and liver physiology, 315(1), G53-G65
Citation
Christiansen, Charlotte Bayer; Gabe, Maria Buur Nordskov; Svendsen, Berit; Dragsted, Lars Ove; Rosenkilde, Mette Marie; Holst, Jens Juul. (2018). The impact of short-chain fatty acids on GLP-1 and PYY secretion from the isolated perfused rat colon.. American journal of physiology. Gastrointestinal and liver physiology, 315(1), G53-G65. https://doi.org/10.1152/ajpgi.00346.2017