The Gut-Brain-Skin Axis: Yes, it's a Thing

*Disclaimer: I am not a registered dietitian, naturopath, doctor, or other type of healthcare professional. This is simply the product of my own research and opinions, not to be used to replace the recommendations of a registered healthcare provider.


Recently, there’s been growing anecdotal evidence, especially in the field of alternative medicine, in favor of treating acne by working to repair the gut microbiome. However, more research is needed in order to take this gut-skin relationship from anecdotal to scientific. In this post, I will discuss some of the current research related to the gut-brain-skin axis; in order to shed some light on some of the potential causes of acne development.


What is a microbiome? The microbiome is all the bacteria, fungi, protozoa and viruses that live inside our gut (or intestines) and on our skin. Think of your body as a donut, where all our insides are built around our digestive tract, which runs all the way from our mouth to our you-know-where. The microbiome is located where we have contact with the outside world – so, our skin and the lining of our digestive tract. Our microbiome is huge, so huge in fact, that it outnumbers our human cells 10 to 1! Why do we care about our gut microbiome? Well, our gut microbiome is essential for our development, immunity and nutrition. It effects how well we digest food, synthesize essential vitamins (like vitamin K and biotin) and harvest calories; as well as contributes to systematic inflammation, which can trigger autoimmune diseases and other inflammatory conditions. Our microbiome is unique to each of us and is determined by a plethora of factors such as what we eat, where we live, if we have pets, if we’re stressed, if we were breast fed or not as babies, and so on.



Acne is a highly prevalent inflammatory skin condition, where many factors are believed to contribute to its development (i.e. increased sebum production and skin inflammatory mediators), but the exact cause still remains unknown. However, it is increasingly believed that the gut microbiota could be involved in the development of acne; where this relationship is further aggravated by mental factors (such as stress). It is hypothesized that stress (including depression and anxiety) aggravates acne by altering the gut microbiota, increasing intestinal permeability and contributing to skin inflammation. This relationship gives rise to the idea of a gut-brain-skin axis, that connects gut microbes, probiotics, and diet to acne severity. So, with that being said, let’s dive into some of the research that attempts to elucidate the gut-brain-skin relationship in the context of acne development.

The Intestinal Barrier

Both the gut and the skin are heavily vascularized organs with important hormonal and immune functions – with recent evidence suggesting that there exists a bidirectional connection between the gut and skin. In addition to evidence that our gut microbiota affects skin through its regulatory effect on immunity, there is also evidence that the gut flora can affect the skin directly. In this way, when the intestinal barrier is damaged, gut microbes and their metabolites can enter the bloodstream, travel to the skin, accumulate in the skin; and disturb the skin’s microbiome. The mechanism of this direct relationship is believed to occur via the mTOR pathway, a cell signaling pathway that regulates cell growth and division; as well as the synthesis of proteins, lipids and cellular material [1]. It is believed that the mTOR pathway my affect the gut microbiota by controlling the intestinal barrier, where in the case of a disturbed barrier, a positive feedback loop can be formed; resulting in an amplified metabolism and inflammation [2]. Essentially, when the intestinal barrier is disturbed, the metabolites that leak out of the gut and enter the bloodstream result in a pro-inflammatory response, in addition to disturbing skin homeostasis, where both these events contribute to the development and aggravation of acne.

Further, this connection between acne and intestinal barrier disturbance can originate in the brain. Experimental studies on both human and animals have concluded that stress impairs the normal gut microflora, causing intestinal microbes to produce neurotransmitters that cross the intestinal wall to enter the blood stream and result in systemic inflammation [3].


Diet

Recently, the role of diet, especially the Western diet, has been raised in acne development. The Western diet is typically referred to as a low-fiber, high-fat diet; which includes dairy products, refined and hyperglycemic carbohydrates and saturated fats (including trans fats). This diet both shapes the activity of our genome, as well as affects our gut microbiota. The high-fat, low-fiber nature of the Western diet reduces the level of gut flora and increases the concentration of lipopolysaccharides, which result in systemic inflammation by impairing the intestinal barrier and increasing the secretion of pro-inflammatory molecules. Disclaimer: “high-fat” is referring to high levels of saturated and trans fats, not healthy fats like mono- and polyunsaturated fats; and omega-3 and 6 fatty acids. Interestingly, in a recent 2018 study, acne patients showed lower gut microbiota diversity, as well as a decrease in bacteria species responsible for suppressing immune response and strengthening the intestinal barrier, relative to patients without acne [4].


It’s recommended that those with acne should control total calorie uptake and restrict sugar, refined carbohydrates, milk, whey, casein protein supplements, saturated fats and trans fats. According to researchers, the ideal “anti-acne diet” is a paleo-like diet high in vegetables and fruits with a low glycemic index and sea fish with anti-inflammatory omega-3 fatty acids. Due to the interplay between the gut, skin and brain, consuming a diet higher in omega-3’s will also result in improved mood and brain function. Additionally, beneficial nutrients for acne include EGCG (found in green tea), resveratrol (in red grapes), curcumin (found in turmeric), genistein (in soy) and silymarin (found in milk thistle) [5]. It’s important to note that a predisposition to acne increases the sensitivity of the Western diet for acne. Additionally, individuals with persistent insulin resistance, hyperinsulinemia (too much insulin in the blood) and hyperandrogenism (such as women with PCOS), will show increased responsiveness to the acne-promoting signals of the Western diet [5]. In short, if you don’t have a predisposition to acne, suffering from acne, or have any of the aforementioned conditions, then there’s no need to eliminate any of these food groups. However, I think that everyone can benefit from being mindful of eating more fruits, vegetables and omega-3’s; and less sugar, refined carbohydrates and saturated fats.



Probiotics

Probiotics are living microorganisms (bacteria) that are beneficial to our health; by providing a protective layer across our intestinal wall. Prebiotics are non-digestible food components that benefit the body by providing food for the bacterial species present in our gut; stimulating their growth and activity. Typically, oral probiotics and prebiotics are used to prevent and treat bowel disease, however growing evidence supports that, by adjusting the composition of the gut microbiome, probiotics induce immune reactions that expand beyond the gut and act on the skin. Further, a 2006 study found that probiotics directly suppressed the growth of C. acnes, the bacteria known to be responsible for acne development, by secreting an inhibitory substance [6]. Further, probiotics have immuno-regulating properties on epithelial cells, where they inhibit the release of pro-inflammatory molecules [7]. Interestingly, a few studies have found that, when probiotics were topically applied, they improved the skin barrier and produced an increase in antimicrobial peptides [2]. Most notably was the increase in ceramide production, which traps water in the skin (strengthening the skin barrier) and displays antimicrobial activity against C. acnes [8].

However, despite these studies demonstrating a positive relationship between probiotic use and acne improvement, it’s important to note that these studies are using carefully isolated probiotic strains in adequate amounts. Many of the probiotics available on the market are sold with too few cultures, not enough strains and contain mostly dead bacteria. Thus, if you’re considering taking a probiotic it’s important to ask a registered health professional for brand recommendations.


Final Thoughts

So, what do we do with all this information? What these studies are NOT trying to do is say that all acne is caused by the gut microbiome. Instead, this research is meant to outline mechanisms supporting the existence of the gut-brain-skin axis; in order to guide the development of new acne treatments (i.e. oral/topical probiotics) and therapeutic targets. If you are struggling with acne, it might be useful to consider seeing a health practitioner about trying a paleo-style diet and/or a probiotic supplement; however, it’s not guaranteed that it will be the answer to all your acne woes. With that being said, even if the gut microbiome is not the root cause of absolutely everyone’s acne, there is still sufficient evidence to support the existence of the gut-brain-skin axis and its potential role in acne development.


Have you noticed changes in your skin from diet or probiotics? Let me know down in the comments!



Sources

[1] Kimura, I., Ozawa, K., Inoue, D., Imamura, T., Kimura, K., Maeda, T., Terasawa, K., Kashihara, D., Hirano, K., Tani, T., Takahashi, T., Miyauchi, S., Shioi, G., Inoue, H., & Tsujimoto, G. (2013). The gut microbiota suppresses insulin-mediated fat accumulation via the short-chain fatty acid receptor GPR43. Nature communications, 4, 1829. https://doi.org/10.1038/ncomms2852

[2] Lee, Y. B., Byun, E. J., & Kim, H. S. (2019). Potential Role of the Microbiome in Acne: A Comprehensive Review. Journal of clinical medicine, 8(7), 987. https://doi.org/10.3390/jcm8070987

[3] Bowe, W. P., & Logan, A. C. (2011). Acne vulgaris, probiotics and the gut-brain-skin axis - back to the future?. Gut pathogens, 3(1), 1. https://doi.org/10.1186/1757-4749-3-1

[4] Deng, Y., Wang, H., Zhou, J., Mou, Y., Wang, G., & Xiong, X. (2018). Patients with Acne Vulgaris Have a Distinct Gut Microbiota in Comparison with Healthy Controls. Acta dermato-venereologica, 98(8), 783–790. https://doi.org/10.2340/00015555-2968

[5] Melnik B. C. (2015). Linking diet to acne metabolomics, inflammation, and comedogenesis: an update. Clinical, cosmetic and investigational dermatology, 8, 371–388. https://doi.org/10.2147/CCID.S69135

[6] Bowe, W. P., Filip, J. C., DiRienzo, J. M., Volgina, A., & Margolis, D. J. (2006). Inhibition of propionibacterium acnes by bacteriocin-like inhibitory substances (BLIS) produced by Streptococcus salivarius. Journal of drugs in dermatology : JDD, 5(9), 868–870.

[7] Cosseau, C., Devine, D. A., Dullaghan, E., Gardy, J. L., Chikatamarla, A., Gellatly, S., Yu, L. L., Pistolic, J., Falsafi, R., Tagg, J., & Hancock, R. E. (2008). The commensal Streptococcus salivarius K12 downregulates the innate immune responses of human epithelial cells and promotes host-microbe homeostasis. Infection and immunity, 76(9), 4163–4175. https://doi.org/10.1128/IAI.00188-08

[8] Pavicic, T., Wollenweber, U., Farwick, M., & Korting, H. C. (2007). Anti-microbial and -inflammatory activity and efficacy of phytosphingosine: an in vitro and in vivo study addressing acne vulgaris. International journal of cosmetic science, 29(3), 181–190. https://doi.org/10.1111/j.1467-2494.2007.00378.x