Scientists have shown that a diet rich in fiber is good for your health. It reduces the risk of many conditions, including cardiovascular disease, type 2 diabetes, and some cancers.
But why? One of the primary ways fiber helps protect health is by feeding your gut microbiome — the trillions of microorganisms in your gut.
As your microbes ferment fiber, they produce short-chain fatty acids (SCFAs). These compounds play a part in the health benefits associated with fiber.
In this article, we’ll take a long stroll into the world of SCFAs and try to figure out how they protect your health.
What are SCFAs?
SCFAs are a group of fatty acids produced when gut bacteria ferment fiber. The most common types are butyrate, propionate, and acetate.
The majority of your gut bacteria produce butyrate, but only some species produce propionate and acetate.
Once your gut bugs have produced SCFAs, most of it is used as energy by the cells lining your gut.
The remaining SCFAs move through your gut wall and enter your blood. Interestingly, these compounds provide around 10% of your daily energy.
Before we get into the weeds, it’s worth noting: Although scientists know that fiber is essential for overall good health and that SCFAs play a part, they’re still figuring out exactly how SCFAs work in the body.
Here, we’ll focus on just a few areas: gut health, blood sugar control, weight maintenance, mineral absorption, and inflammation.
One of SCFAs’ most vital roles is supporting your intestinal epithelial cells — the cells that line the inside of your gut.
These cells are important in many ways. For instance, they help you digest your food and absorb nutrients. And they help protect against infections and produce mucus.
This layer of cells also contains so-called neuroendocrine cells that can pump hormones into the bloodstream to communicate with the nervous system.
SCFAs are the primary fuel source for these cells, keeping them powered up and fully functioning.
Beyond energy, SCFAs also help keep epithelial cells tightly linked together. This reduces the risk that unwanted compounds might leak into the bloodstream.
All in all, without SCFA-producing bacteria, our gut health would struggle.
Next, we’ll look at other ways SCFAs might benefit health, although scientists are still working out the details.
Blood sugar response
After you eat, digestible carbs are broken down into glucose and enter your blood.
This causes a rise in blood sugar, which is normal: Your body needs glucose to fuel your cells, and blood takes it where it’s needed.
However, if blood sugar spikes are repeatedly pronounced, this increases the risk of developing health conditions over time, such as cardiovascular disease.
Eating fiber helps reduce your blood sugar response following a meal. This is partly because fiber takes longer to break down, so sugar can’t be absorbed into your blood so quickly. However, SCFAs may also play a part.
For instance, some SCFAs bind to receptors and trigger the release of two hormones from gut cells. They’re called GLP-1 and peptide YY, and they lower blood glucose in two ways:
They stimulate insulin release, which helps move glucose out of your blood and into your cells.
They slow the release of glucagon — a hormone that usually increases blood sugar levels.
SCFAs might influence your blood sugar response in other ways, too. According to the authors of a review, SCFAs also influence:
Glycolysis: how liver cells break down sugar to make energy.
Gluconeogenesis: a process whereby liver cells make glucose from compounds other than carbs.
Glycogen synthesis: Your body converts some sugar to glycogen, which acts as an emergency energy store.
Scientists are still figuring out how much impact SCFAs have on blood sugar responses after a meal. It’s a complex business.
It’s worth noting that much of the research today has been carried out in the lab, on animals or with people who have prediabetes or diabetes. So, it’s not clear what their effect might be for other folk.
Also, because fiber improves glucose control in more than one way, it’s tricky to tease out the precise role of SCFAs.
There is some evidence that SCFAs play a part in maintaining a healthy weight. Experts think they might do this through a few routes.
Firstly, GLP-1 and peptide YY — which are released in response to SCFAs — increase the sensation of feeling full. This could potentially reduce how much food someone eats.
Secondly, SCFAs act on fat cells, promoting the release of a hormone called leptin, which also reduces appetite.
There’s also some evidence that the SCFA acetate might travel from your gut to your brain. Once there, it can suppress hunger. However, this was discovered in a mouse study, and you're not a mouse.
Glucose and weight: Evidence in humans
Although SCFAs are only part of the picture, it seems likely that they help control blood sugar levels and maintain a healthy weight. The evidence isn’t watertight yet, but it’s slowly building.
For instance, in one study, participants with diabetes ate either a high- or low-fiber diet for 12 weeks. By the end, those consuming the fiber-rich diet had more types of gut bacteria that produce SCFAs.
The researchers found that participants on the high-fiber diet had increased levels of GLP-1 and better blood glucose control. These participants also lost more weight than those on the low-fiber diet.
Join our mailing list
Sign up for fresh insights into our scientific discoveries and the latest nutrition updates. No spam, just science.
Another human study provides more direct evidence of the role of SCFAs in weight.
The scientists recruited 60 adults with overweight. They focused on one SCFA — propionate. Participants took propionate daily for 24 weeks.
The researchers found that, compared with a control group, those taking the SCFA had higher levels of PYY and GLP-1 in their blood. They also had a reduced energy intake.
Notably, the authors also found that the SCFA group gained less weight than those in the control group.
However, not all studies have found links between SCFAs and weight loss. We need more clinical trials before we can reach solid conclusions.
And, as with glucose control, fiber helps maintain a healthy weight in a few different ways, so it’s challenging to pin down the precise role of SCFAs.
Your body needs various minerals to work effectively and grow, such as calcium, potassium, chloride, magnesium, and sodium.
As with other nutrients, minerals travel from your gut, through the gut wall, and into your blood.
SCFAs may help increase mineral absorption in more than one way.
For instance, SCFAs are acids, so they make the gut slightly more acidic. This makes minerals more soluble and easier to absorb. As an aside, this also helps ward off “bad” gut bacteria.
SCFAs also stimulate the development of intestinal wall cells, helping increase the surface area of your gut. A larger surface area means more mineral absorption.
But, as the authors of a review explain, much of the current research involves healthy participants. So, scientists need to study people with mineral deficiencies to understand how important SCFAs are in this process.
Inflammation is a healthy immune response to infection or injury. However, if inflammation continues over the long term, it can cause damage to your body.
SCFAs may influence inflammation. And some evidence suggests they could play a role in treating people with inflammatory bowel disease (IBD).
People with IBD have a “leaky gut.” This means that potentially harmful substances can leak through the gut wall and enter the bloodstream. In response, the immune system triggers inflammation.
Because SCFAs nourish and repair the cells that line the gut, scientists have wondered whether SCFAs might help reduce the symptoms of IBD. In fact, scientists have been investigating SCFA enemas since the 1990s.
In a small study from 2002, researchers recruited individuals with ulcerative colitis, a form of IBD. They treated participants with either an SCFA (butyrate) enema or a placebo enema twice daily for around 8 weeks.
The researchers found that those who had the butyrate enema had a reduced immune response and improved symptoms. However, not all enema studies had such positive results.
Now, researchers are focusing on ways to encourage the growth of bacteria that produce SCFAs using probiotics and prebiotics to help treat IBD.
Inflammation beyond IBD
Currently, it's not clear what role SCFAs play in inflammation in people without IBD. Although much of the research has been carried out in people without gut conditions, the results are mixed.
This makes sense — people without IBD may not have much inflammation.
Also, because inflammation is a healthy response to infection or injury, reducing it might not be the best course of action in people without ongoing inflammation. So, SCFAs might not need to get involved.
The gut is a complex place for the immune system — it has to ward off bugs that will make you sick while protecting the “good” bugs that keep you well.
Some research suggests that SCFAs might help keep the balance by mediating between “good” gut bacteria and your immune system.
Although we don’t have all the answers, many immune cells have receptors for SCFAs. This hints that they’re playing an important role in inflammation and beyond.
Much more to learn
SCFAs are produced as gut bacteria ferment fiber. They seem to be involved in processes throughout the body. But, as we’ve seen, researchers are still working on many of the details.
To fully understand how these compounds influence human health, scientists need to carry out more human studies.
However, we do know that eating a diet high in fiber can benefit health. That’s a fact.
And the best way to increase your fiber intake is to eat more plants. So, whether SCFAs are miracle workers or not, adding a variety of plants to your diet will certainly benefit your long-term health.
Butyrate inhibits NF-kappaB activation in lamina propria macrophages of patients with ulcerative colitis. Scandinavian Journal of Gastroenterology. (2002). https://pubmed.ncbi.nlm.nih.gov/11989838/
Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet. (2019). https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)31809-9/fulltext
Effect of butyrate enemas on the colonic mucosa in distal ulcerative colitis. Gastroenterology. (1992). https://pubmed.ncbi.nlm.nih.gov/1612357/
Effects of targeted delivery of propionate to the human colon on appetite regulation, body weight maintenance and adiposity in overweight adults. Gut. (2015). https://gut.bmj.com/content/64/11/1744.short
Energy contributions of volatile fatty acids from the gastrointestinal tract in various species. Physiological Reviews. (1990). https://journals.physiology.org/doi/abs/10.1152/physrev.19184.108.40.2067
From dietary fiber to host physiology: Short-chain fatty acids as key bacterial metabolites. Cell. (2016). https://www.sciencedirect.com/science/article/pii/S009286741630592X
Glucagon-like peptide 1. (2022). https://www.yourhormones.info/hormones/glucagon-like-peptide-1/
Gut bacteria selectively promoted by dietary fibers alleviate type 2 diabetes. Science. (2018). https://www.science.org/doi/abs/10.1126/science.aao5774
Leptin. (2018). https://www.yourhormones.info/hormones/leptin/
Metabolites produced by commensal bacteria promote peripheral regulatory T-cell generation. Nature. (2013). https://www.nature.com/articles/nature12726
Peptide YY. (2022). https://www.yourhormones.info/hormones/peptide-yy/
Postprandial hyperglycemia on vascular endothelial function: mechanisms and consequences. Nutrition Research. (2012). https://www.sciencedirect.com/science/article/abs/pii/S0271531712001637
Prebiotics, probiotics, and synbiotics affect mineral absorption, bone mineral content, and bone structure. The Journal of Nutrition. (2007). https://academic.oup.com/jn/article/137/3/838S/4664776
Regulation of Intestinal Epithelial Cells Properties and Functions by Amino Acids. BioMed Research International. (2018). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5966675/
SCFA: mechanisms and functional importance in the gut. Proceedings of the Nutrition Society. (2020). https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/scfa-mechanisms-and-functional-importance-in-the-gut/6EC53433CF2A6B17F009D1B333C0BC59
Short-chain fatty acids in control of body weight and insulin sensitivity. Nature Reviews Endocrinology. (2015). https://pubmed.ncbi.nlm.nih.gov/26260141/
Short chain fatty acids (SCFAs)-mediated gut epithelial and immune regulation and its relevance for inflammatory bowel diseases. Frontiers in Immunology. (2019). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6421268/
The relationship between gut microbiota, short-chain fatty acids and type 2 diabetes mellitus: The possible role of dietary fibre. Acta Diabetologica. (2021). https://link.springer.com/article/10.1007/s00592-021-01727-5
The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism. Journal of Lipid Research. (2013). https://www.jlr.org/article/S0022-2275(20)35124-5/fulltext
The short-chain fatty acid acetate reduces appetite via a central homeostatic mechanism. Nature Communications. (2014). https://www.nature.com/articles/ncomms4611