May 04, 2022 8 min read
May 4, 2022
Short-chain fatty acids (SCFAs) are simply metabolic magic made by the microbes living in your gut. They are made when your gut bacteria ferment (break down) the carbohydrates in your diet and are essential for many aspects of your health.
In this article, we explore what short-chain fatty acids are, why they’re important and how you can help to boost their production. So, sit tight as we take you on a journey of discovery that starts as soon as you eat.
Short-chain fatty acids are made in the gut by the friendly bacteria that reside there. Your body isn’t equipped with the enzymes needed to digest dietary fibre, so your gut bacteria do it for you.
In this article, we are going to explore the SCFAs:
Technically, lactate isn’t a short-chain fatty acid, but it is an important metabolite produced by lactic acid bacteria that has many beneficial effects, so it’s important to explore its role in the body.
The human gut microbiome is an extraordinary ecosystem that resides in the gastrointestinal tract. It is home to trillions of bacteria as well as protozoa, archaea, and viruses that live symbiotically within the gut.
The gut microbiome consists of bacteria from three important phyla. They are:
A diverse microbiome serves as an expansion of our genome. That’s because the gut microbiome is estimated to have between 50 and 100-fold more genes than we have alone.
Gut bacteria produce beneficial metabolites called short-chain fatty acids when they ferment dietary fibre and resistant starch. The expansion of genes means the gut microbiome brings with it proteins and enzymes that our body doesn’t have, such as those needed to digest fibre, and has a great impact on our metabolism and physiology as a whole[i].
So, when you eat dietary fibre, certain bacteria in your colon are responsible for fermenting it and transforming it into short-chain fatty acids. These compounds are important for human health and have many roles within the body.
Short-chain fatty acids are known to improve gut health by:
Acetate is the most abundant SCFA in the human gut, making up over half of the total SCFAs detected in faeces. Most of the acetate is produced by bacteria when they breakdown dietary fibre[iii].
As fibre travels through the GI tract bacteria such as Bifidobacteria and Lactobacillustransform it into acetate. Then, by a process called cross-feeding, acetate can be used by other bacterial species to produce butyrate, a critical source of energy for the cells that line your gut, called colonocytes.
Research shows that one of the main functions of acetate is its role in regulating body weight and insulin sensitivity. It does this by binding to receptors in the gut lining which are important for releasing the gut hormones peptide YY and glucagon-like peptide-1 (GLP-1), both of which are involved in appetite regulation.
GLP-1, for example, delays gastric emptying which is where the contents of the stomach move from the stomach to the intestines. By slowing the emptying of the stomach, GLP-1 helps to keep you feeling fuller for longer, suppressing your appetite[iv].
Furthermore, a study conducted by Nogal et al (2021) found that higher levels of acetate within the blood are associated with lower visceral fat. The study identified six serum acetate producing bacteria, notably Coprococcus, which may have a positive effect on host health, and Lachnoclostridium, which was shown to have a negative effect on circulating acetate levels[v].
This is important because it has been suggested that Lachnoclostridium produces a harmful fat compound called trimethylamine-N-oxide, or TMAO for short. TMAO is associated with an increased risk of becoming obese or developing type 2 diabetes[vi].
Despite being the least produced SCFA in the body, butyrate has many vital benefits for human health, including anti-inflammatory properties. The great thing about butyrate is it is super simple to boost its production by your gut microbes, simply by eating plenty of prebiotic fibre (that type that keeps your gut inhabitants nourished).
The main bacterial producers of butyrate are members of the Firmicutesphyla, particularly Faecalibacterium prausnitzii, Clostridium leptum, Eubacterium rectale,and Roseburia[vii].
Butyrate has numerous functions in the human body. Its most important role is it is the main energy source for the cells that line the gut, called colonocytes.
Just like you, these cells need energy to carry out their important jobs, and in the case of colonocytes, their main job is to maintain the integrity of the gut lining. The lining of the gut is a barrier between the gut and the rest of the body, so if this is compromised it can lead to toxins, pathogens, and even food entering the bloodstream, increasing the risk of inflammation and illness.
That’s not all. Butyrate also has powerful antioxidant properties and has been shown to protect against inflammation, obesity, and cancer[viii]. Butyrate also helps to boost intestinal mucosal immunity, playing a key role in cell proliferation (growth) and apoptosis, effectively cell suicide[ix]
The least studied of all the SCFAs, propionate has several benefits for human health. It’s produced by bacteria from the Bacteroidetes and Firmicutes phyla. Just like other SCFAs, gut bacteria produce propionate when they break down dietary fibre.
More recent research is pointing towards propionate having a key role in the development of metabolic diseases, such as obesity and type 2 diabetes.
Studies have shown that, just like acetate, propionate also increases the release of specific hormones that help to keep you feeling full, thus suppressing your appetite. In a 2015 study, researchers showed that increasing propionate in the gut helped to prevent weight gain in overweight adults[x]
Interestingly, propionate is also used in food manufacturing and is often used as a preserving agent. In mice, when propionate is used in this way, it is associated with weight gain and insulin resistance[xi].
Propionate, like butyrate, also has potent anti-inflammatory properties and research shows it could have the potential to treat inflammatory disorders, like inflammatory bowel disease (IBD)[xii].
Lactate isn’t actually a short-chain fatty acid, but it is an important bi-product produced when certain gut bacteria ferment fibre[xiii]. Lactate, as its name suggests, is produced by lactic acid bacteria, such as Lactobacillus.
The lactate produced by lactic acid-producing species can be used for cross-feeding other gut microbes. For example, some bacteria can use lactate to make butyrate, which also has many vital roles for the gut and body, particularly in maintaining the integrity of the gut lining. So, in effect, by increasing the abundance of bacteria such as Lactobacillus,you will be increasing the abundance of butyrate, and that can only mean good things for your gut.
That’s not all. Lactate is also an important component of fermented foods, like kimchi, yoghurt and pickled vegetables. Because these foods contain live bacteria that have health-promoting properties, they are often referred to as “functional foods.” Consuming these foods as part of a normal, healthy diet can help to diversify and modulate the intestinal community, boost immunity, and improve energy metabolism[xiv].
Human milk oligosaccharides (HMOs) are complex sugars present in human breast milk. HMOs are considered to be prebiotic, which means they help to nourish the beneficial bacteria in the gut, enabling them to thrive and survive. More recent research has shown that HMOs are not just food for microbes, but they also prevent pathogens from adhering to the mucosal surfaces. So, they also help to lower the risk of infection, too[xv].
By helping to nourish, for example, Bifidobacteriaand Lactobacilli, HMOs contribute to the production of SCFAs, and thus help to unleash their health-promoting benefits[xvi].
Short-chain fatty acids are powerful bi-products produced by your gut bacteria during carbohydrate fermentation. Acetate, butyrate and propionate account for 95% of the short-chain fatty acids produced in the human body.
SCFAs are essential for both your gut and overall body health and have been linked to a lower risk of many chronic conditions. The production of SCFAs can be boosted by the foods you eat, but supplementation with HMOs is also an easy way to help promote and maintain gut health.
Written by: Leanne Edermaniger, a science writer who specializes in human health and enjoys writing about all things related to the gut microbiome.
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