Why are short-chain fatty acids important?

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.

Gut health

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: 

1. They stimulate insulin release, which helps move glucose out of your blood and into your cells. 

2. 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.

Weight control

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.

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.

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.

Inflammation control

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.