What Are Short-Chain Fatty Acids and Why Do They Matter?

You’ve heard that you should eat more fiber. But why?

There may be several benefits to fiber, but one of them doesn’t come from the fiber itself. It comes from a byproduct.

Your gut microbiome, the community of trillions of bacteria in your colon, makes molecules known as short-chain fatty acids (SCFAs). These molecules are getting more and more attention for their roles in gut health.

What Are Short-Chain Fatty Acids?

Short-chain fatty acids (SCFAs) are made when bacteria in your colon ferment dietary fiber. There are three main types: acetate, propionate, and butyrate.

Fatty acids are the building blocks of a larger group of molecules called lipids. The best-known lipids are triglycerides, or common “fat”. Triglycerides are made up of fatty acids and hold a lot of energy that the body can use. Fatty acids can also build structures or be turned into signals that start various processes throughout the body.

Fatty acids are essentially chains of carbon with hydrogen bonded to them. The number of links, or carbons, in the chain determines the length. SCFAs have the fewest links, so they’re the shortest.

SCFAs have been documented in research for decades. A 1987 article discussed emerging evidence that dietary fiber is not digested but instead fermented by bacteria in the colon. That fermentation is what makes SCFAs.

When researchers measured SCFA levels along the gut at autopsy, they found them concentrated in the colon, which suggests that’s where they’re made.

So, once SCFAs are made in the gut, where do they go?

Where Do They Go?

So, once SCFAs are produced by your gut bacteria, where do they go?

A study of 12 healthy adults set out to answer that. Researchers gave subjects capsules that released tagged SCFAs in the colon, so they could track how SCFAs traveled through the body.

Within 12 hours, much of each SCFA was burned for energy and breathed out as CO2. Some were used to make glucose, and some ended up in fat.

SCFAs that are absorbed from your gut first travel to the liver, where a large portion of them are used for metabolism. From there, only a fraction make it past the liver into your general bloodstream.

Butyrate

Butyrate usually doesn’t travel very far. Only about 2% reaches your bloodstream, because the cells of your colon burn it as their main source of energy. That energy keeps them from dying off.

As colon cells burn up butyrate, the process uses up oxygen, leaving a low-oxygen environment in the gut. That suits butyrate-producing bacteria and keeps harmful bacteria away. So butyrate producers make more butyrate, the cycle continues, and gut cells keep getting their energy.

Propionate

About 9% of propionate reaches the bloodstream. The autopsy study points to the liver as its main stop. There, some of it is used in a process known as gluconeogenesis. That refers to the liver creating new glucose from other materials.

Acetate

Out of the three main SCFAs, acetate reaches the general bloodstream in the largest proportion. In circulation, SCFAs like acetate can affect the function and metabolism of the liver, pancreas, fat cells, immune cells, and muscle.

When researchers traced acetate through the body, about a quarter of it was turned into butyrate, which gives your gut cells energy.

Short-Chain Fatty Acids Benefits

SCFAs are signalers. They carry messages between the food you eat, your gut bacteria, and your body.

SCFAs can provide energy to your gut cells in the form of butyrate, but they can also help the gut lining make new cells. Butyrate is able to strengthen the gut barrier. It switches on genes that create tight junctions, proteins that seal gaps between cells of your gut lining. This helps your gut defend against harmful substances that end up there. Butyrate also helps produce anti-microbial peptides, small proteins that protect against harmful bacteria.

SCFAs can calm inflammation by signaling your immune system. People with inflammatory bowel disease (IBD) tend to have fewer SCFA-producing bacteria. It’s unclear whether the IBD causes that loss, or if fewer SCFAs lead to the inflammatory state that’s common in IBD.

SCFAs activate receptors on your gut cells that release GLP-1 and PYY, hormones that influence digestion and feeling full. In one study of 160 adults, SCFA levels in the blood were linked to GLP-1 levels. In another, researchers gave subjects a form of propionate built to reach the colon. Their GLP-1 and PYY went up and they ate about 14% less at their next meal even though they didn’t report feeling any less hungry.

SCFAs are also speculated to have a key role in the conversation between your gut and your brain. They might be able to influence your mood and thinking through nerves, hormones, and effects on the immune system.

Many studies test SCFAs directly using pure supplements. Most of the SCFAs in your body weren’t eaten directly. Instead, they come from fiber that’s been fermented by your gut bacteria. The more reliable way to raise your SCFAs is to feed your gut bacteria fiber.

How to Get More Short-Chain Fatty Acids

Non-digestible carbs, like fiber, can change which bacteria live in your gut and what they do. That’s because fiber feeds your beneficial bacteria and helps them grow.

Many of the fibers your bacteria ferment are prebiotics. In common terms, a prebiotic is most often a fiber that your own body can’t digest, which your gut bacteria eat for energy.

Several prebiotics exist naturally in whole foods:

• Asparagus
• Sugar beet
• Garlic
• Onion
• Jerusalem artichoke
• Wheat
• Honey
• Banana
• Barley
• Tomato
• Milk
• Peas
• Beans

One study had 174 college students add different types of fiber supplements to their normal diet for two weeks. Raw potato starch raised butyrate by about 29% on average. However, responses varied a lot from person to person and seemed to depend on a person’s existing microbiome. The bacteria you have in your gut might be a deciding factor for how much SCFA your gut makes, at least in the short term.

Because of this, researchers say the usual idea that any fiber supplement will raise your butyrate may be an oversimplification.

So, it may help to mix up your fiber sources and types, since different microbiomes seem to respond to different fibers.

Should You Take a Butyrate Supplement?

There are some butyrate supplements currently available to buy. But should you be taking one if you want to experience the beneficial effects associated with SCFAs?

It gets complicated to give a certain answer, because it isn’t clear how much swallowed butyrate actually reaches your colon.

Butyrate does most of its known work in the colon, so you’d want to know a supplement actually gets there.

It’s also hard to isolate the effects of butyrate supplementation in the research, since some studies use combination products of butyrate plus something else.

For now, there doesn’t seem to be solid evidence that a butyrate supplement can do what fiber does.

In Summary

SCFAs are potentially one of the most surprising benefits of eating fiber. They fuel your gut cells and can send signals that regulate other important functions in your body.

Research on everything SCFAs do is still emerging, but it’s exciting. There could be implications for aiding digestion, immunity, and even cognition.

SCFAs show why there’s no shortcut around eating enough fiber. If fiber intake is reduced and SCFA-producing bacteria are starved, your gut could be missing out on those benefits, and maybe even decline in function.

For now, the best-supported way to maximize your chances of good SCFA output is by eating a whole-food diet rich in fiber. That feeds the bacteria that make SCFAs and helps them multiply.

You’ve heard that you should eat more fiber. Now you know one of the reasons why.