Growing evidence suggests that short chain fatty acid enemas have effects on various organs including the brain. The new research on the effects of SCFAs show that gut health may have a connection to mental health. Dysbiosis of the gut microbiota has been implicated in the pathology of conditions like depressions and Alzheimer’s. Now that this connection is better understood, researchers are considering whether SCFAs and be use as a treatment to improve the gut microbiota and in connection improve these conditions related to the brain.

What is a Short Chain Fatty Acid?

Short chain fatty acids (SCFAs) are the product of anaerobic fermentation of polysaccharides (dietary fiber and resistant starch) that are indigestible. The main SCFAs are butyrate, acetate, and propionate – with the highest proportion being acetate. SCFAs have a number of benefits and are essential for gastrointestinal health. Patients with gastrointestinal disorders frequently have depleted levels of SCFAs. Local effects include maintaining the intestinal barrier, reducing inflammation, and reducing the risk of colorectal cancer.

SCFAs and the Brain

The effects of SCFAs are not just localized to the gut however. Microbiota-gut-brain-crosstalk refers to the effects of the gut microbiome on the brain and vice versa. There are several ways that SCFAs may influence brain health. They may cross the blood-brain barrier through endothelial cells that have a high number of monocarboxylate transporters (MCTs). Levels of butyrate, acetate, and proprionate are all detectable in human cerebrospinal fluid (CSF).

SCFAs may also modulate the levels of neurotransmitters. These metabolites have been shown to regulate the expression of tryptophan 5-hydroxylase 1 and tyrosine hydroxylase.

Tryptophan 5-Hydroxylase 1

• Involved in the synthesis of serotonin.
• Serotonin reuptake inhibitors (SSRIs) are prescribed to treat depression. They prevent the reabsorption of serotonin after it has transmitted its signal, elevating the circulating levels of this neurotransmitter.

Tyrosine Hydroxylase

• Involved in the synthesis of dopamine, noradrenalin, and adrenaline.
• Dopamine is another neurotransmitter that is associated with motivation.

Dopamine and serotonin are both neurotransmitters that have been studied in association with mental health conditions. SCFAs have been shown, through regulating the expression of tryptophan 5-hydroxylase 1 and tyrosine hydroxylase, to have an effect on dopamine and serotonin.

The Microbiota-Gut-Brain Axis

Each person has trillions of microorganisms living inside of them. Collectively these microorganisms are referred to as the microbiota. Gut microbes have an effect on the central nervous system and states of mind. Certain types of bacteria are known to affect the production of neurotransmitters like serotonin and GABA. The communication between the gut and the brain is bidirectional. Neurotransmitters can affect metabolism and the proper functioning of the gut while the gut produces microbes and short chain fatty acids that affect neurotransmitters.

Producing SCFAs

The body naturally produces short chain fatty acids. This production can be lower in individuals with certain gastrointestinal conditions and can be affected by diet. Since SCFAS have been shown to have many beneficial effects, many healthcare providers will recommend a diet that helps increase their levels. This is mainly accomplished through eating a diet high in fiber.  The fiber in food is composed of chains of oligosaccharides. The oligosaccharides are not easily digestible but serve as food for gut microbes. SCFAs are the main metabolite produced by the fermentation of the indigestible fiber. High-fiber diets include vegetables and fruits including onions, beans, broccoli, apples, berries, avocados, and more.

Researchers have studied and continue studying the potential of supplementing short chain fatty acids directly through enemas and suppositories. This may be a beneficial treatment for individuals with gastrointestinal conditions that cause a decreased production of SCFAs. Enemas and suppositories that include acetate, propionate, and butyrate can be made by a compounding pharmacy.

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The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication – Frontiers in Endocrinology