Short-chain fatty acids, also known as SCFAs, are compounds produced by our good gut microbes. They have an important role in human health, stretching from our liver to our brain. Scientists are uncovering the role of these compounds, from the food we eat to the way they are used around the body.

Their chemical character

Short-chain fatty acids are made in our gut when good microbes ferment compounds from our food or other compounds in our body.

These starting compounds can be long carbohydrate molecules including dietary fibre and resistant starch, which human bodies can’t digest. Instead, fibre is broken down by microbes in our gut.

Short-chain fatty acids can be made from other compounds found in the gut too, like protein, sugars and mucins.

During fermentation gut microbes break down these long compounds into smaller ones.

The ‘short-chain’ part of short-chain fatty acids describes that they contain five or less carbon atoms. This differentiates them from medium chain (five to ten carbons) and long chain (more than ten) fatty acids.

They are known as fatty acids because their chemical structures are aliphatic hydrocarbons which repel water molecules. Short chain fatty acids have a range of distinctive smells.

Three common short chain fatty acids are:

• Acetate – contains two carbons
• Propionate – contains three carbons
• Butyrate – contains five carbons

Good for your gut

Around 35g of short-chain fatty acids are produced in the gut each day. The exact amount varies depending on how much fibre you have eaten, the type microbes living in the gut and how long digestion takes.

For example, peas high in resistant starch increase the amount of short chain fatty acids in the large intestine.

While in the gut, short-chain fatty acids improve gut health. They help maintain the lining of the gut by providing energy for the cells that line the gut. This helps strengthen the gut barrier function, stopping toxins and disease-causing microbes entering the blood. A strong gut barrier means that vitamins and minerals enter the blood stream more easily.

Short chain fatty acids are important for protecting the gut from being overrun by bad disease-causing bacteria in another way too. They have protective ability due to their low pH which means they are slightly acidic.

The amount of short-chain fatty acids in the gut is often used as an indicator of the health of fermentative microbes. The presence of the compounds is associated with beneficial bacteria such as Dialister, Streptococcus and Roseburia.

Researchers at the Quadram Institute have shown how probiotics of Bifidobacterium and Lactobacillus bacteria increased the amount acetate in babies. This acetate comes from sugars in breast milk, called human milk oligosaccharides, which are broken down by the bacteria.

Lunch for the liver

Short-chain fatty acids have beneficial effects beyond the gut. In the gut they are absorbed in the blood stream where they can travel to other organs around the body.

In the liver short-chain fatty acids provide energy for liver cells. They acids act as building blocks for the liver to make other substances like cholesterol, glucose and fats.

Importance in inflammation

One way short-chain fatty acids benefit our health is through anti-inflammatory effects.

Studies have shown that lower levels of the compounds are associated with diseases such as colon cancer, ulcerative colitis and diabetes.

Short-chain fatty acids regulate immune cells called leukocytes. It is thought they do this through interacting with specific receptors called G protein receptors.

Role in brain health

Short-chain fatty acids appear to play a role in gut-brain communication.

In many brain diseases there is a change in the amount of short-chain fatty acids in the gut. Quadram Institute researchers found that there were less bacteria that can produce buyrate in the gut microbiome of people with Parkinson’s disease, compared to the gut microbiome of people without the disease.

Here at the Quadram Institute, we are discovering more about short-chain fatty acids from the food we eat, their role in the complex ecosystem of the gut microbiome, and their effects across the human body.