Prebiotics and Mood, Part 1
Prebiotics are food for the good gut microbes that may improve your mood.
The food you eat can have as profound an effect on your brain as the drugs you take. –Dr. Uma Naidoo
Depression, according to the World Health Organization, is the number-one cause of disability today. The loss of productivity costs the global economy a staggering trillion dollars a year. Psychiatry has responded with therapy and drugs, but with mixed success.
The notion that the gut and the brain are somehow connected has presented psychiatry with a new paradigm: Gut microbes may, directly or indirectly, cause or prevent anxiety and depression. This begs the question: As well as treating the mind, should psychiatrists also be treating the gut?
The basic thesis of the gut–brain axis is that our gut can become unbalanced, with a few unsavory bacteria dominating the mix. This imbalance can lead to a “leaky gut,” allowing toxins and bacteria to enter the bloodstream. From there, they are pumped to every organ in the body, including the brain.
This systemic inflammation can cause anxiety in a matter of seconds. Think of how quickly food poisoning can get your attention. Over time, chronic inflammation can lead to a shocking number of diseases, including heart disease, type 2 diabetes, arthritis, and dementia.
In addition to inflammation, your gut microbes can directly produce neurotransmitters like dopamine and serotonin, two important targets of psychoactive drugs. These communication chemicals are used by microbes to talk to each other, but also to talk to us via the vagus nerve that winds its way from the gut to the brain.
There has now been quite a lot of research on the use of probiotics to rebalance our gut microbes, and there has been some notable success. Probiotics that can improve our mood are called psychobiotics, a name coined by prolific investigators John Cryan, Catherine Stanton, and Ted Dinan of University College Cork, in Ireland. Most probiotics don't colonize the gut, but they produce gut-friendly chemicals as they pass through.
What Prebiotics Are
Recently, Cryan and Dinan have expanded the definition of psychobiotics to embrace prebiotics—the food for probiotics. These include substances called oligosaccharides, which are complex sugars that our body can’t digest, but our microbes can. This microbial manna also has a more prosaic name: fiber.
When our gut microbes are fed these prebiotics, they produce substances called short-chain fatty acids, which act to both heal and nourish the cells lining the gut. This puts a damper on leaky-gut syndrome, quenching inflammation and returning our brains to business as usual.
A recent Brazilian study found that prebiotics modified the composition of the microbiota, which, in turn, improved the growth and repair of intestinal tissue. A new Chinese study found that two different oligosaccharides, at a dosage of 1 to 5 grams per day, reduced symptoms of depression. The two prebiotics were galacto-oligosaccharide (GOS) and a polyphenol derived from green tea, epigallocatechin gallate (EGCG).
The authors say, “The plausible mechanisms underlying the impact of prebiotics on depression include the synthesis [by gut microbes] of neurotransmitters, production of short-chain fatty acids, and regulation of inflammation.” That’s an amazing feat for a bunch of tiny microbes.
Next week, we’ll talk about how to put this amazing research to work to keep both you and your gut microbes happy.
References
Yang, Yongde, Bi Zhou, Sheng Zhang, Liang Si, Xiaobo Liu, and Fu Li. “Prebiotics for Depression: How Does the Gut Microbiota Play a Role?” Frontiers in Nutrition 10 (July 6, 2023): 1206468.
Corrêa, Renan Oliveira, Pollyana Ribeiro Castro, José Luís Fachi, Vinícius Dias Nirello, Salma El-Sahhar, Shinya Imada, Gabriel Vasconcelos Pereira, et al. “Inulin Diet Uncovers Complex Diet-Microbiota-Immune Cell Interactions Remodeling the Gut Epithelium.” Microbiome 11, no. 1 (April 26, 2023): 90.
Dinan TG, Stanton C, Cryan JF. Psychobiotics: a novel class of psychotropic. Biol Psychiatry. 2013 Nov 15;74(10):720-6. doi: 10.1016/j.biopsych.2013.05.001. Epub 2013 Jun 10. PMID: 23759244.