How Prebiotics, Probiotics, and the Gut Microbiome are Related to Skin Health
Much has been written in recent years about the gut microbiome and the "good" bacteria in our gut. What is the gut microbiome, and why is it so important for our health and our skin health?
First, we now know that the microbes that live in our gastrointestinal tract play an important role in keeping us healthy. These beneficial microbes play a role in helping us digest our food, and they help us extract nutrients from that food. They also play an important role in helping to train our immune system.
Why has there been such a rise in food allergies?
One of the biggest questions in modern-day healthcare is why, in developed countries, have the rates of allergic diseases risen so dramatically in the last few decades? Why are we seeing such a dramatic rise in food allergies, asthma, and atopic dermatitis? Growing up, I don't remember hearing about anybody who had a peanut allergy. Now, many of my friends have children with nut allergies.
One of the theories behind the rise in allergic conditions is called the "hygiene hypothesis". The theory is that in recent years, our immune system just hasn't been properly trained to distinguish between truly harmful agents [such as dangerous bacteria] and everyday exposures [such as pollens and animal dander]. Our immune system hasn't been trained because we're just not being exposed to as many germs, animals, and plants.
It's what I call the "friendly dog/ scary dog" hypothesis.
Have you ever seen how a child reacts to a friendly dog? For children who haven't grown up around dogs, that curious sniff and that friendly bark can be very frightening. If you've grown up around dogs, though, you know that there's nothing to be alarmed about. You know exactly how to distinguish between the signs of a friendly dog (curious sniff, friendly bark) and the signs of a dangerous dog (growling, staring, menacing look). It's the same with our immune system. One theory is that to keep our immune system working well, you have to train it. You have to train it so that it knows the difference between a friendly dog (pollens, animal dander) and a dangerous dog (dangerous strains of bacteria).
What do the microbes in our gut have to do with our immune system?
One theory relates to the good microbes that live in our gut. Those good microbes are considered "friendly germs", and they help teach our immune system how to tell the difference between the friendly germs and the dangerous ones.
The gut is actually considered an important part of the immune system. And studies indicate that the microbes that live in our gut can help to train our immune system. In one study, certain strains of gut microbes regulated the expression of genes that impacted the immune system. [Hemarajata]. If your immune system hasn't been trained properly, it starts to get very jumpy. It starts to overreact to everything--pollens, trees, animal dander, and even sometimes the cells and parts of our own body. For people with an over-reacting immune system, they may develop allergies and sometimes even autoimmune diseases.
Because of these important effects, our gut microbes have the potential to impact our body in ways that go far beyond just our GI system.
What are the microbes that live in our gut?
There's been a lot of research into the communities of microbes that live in our gut, which are collectively known as the microbiota. There's also been research into the genes of these microbes, collectively known as the microbiome. [Turnbaugh]
Every individual has a distinct and complex microbiome. This can change over time, and can definitely be impacted by the foods that we eat. The microbiome is huge--it's made up of trillions of bacteria and other microbes. (Picardo & Ottaviani)
The foods we eat directly impact our gut microbiome.
We now believe that the gut microbiome has many effects on our health, as well as on our skin health. It's not just allergic diseases that may be impacted by our gut microbiome. Studies have linked the gut microbiome to obesity, depression, and other chronic illnesses. In terms of our skin, a healthy gut microbiome may play a role in maintaining skin hydration, countering skin inflammation, and fighting the damaging effects of free radicals.
In fact, studies in atopic dermatitis have supported the use of supplements that support a healthy gut microbiome. In one summary study, researchers looked at trials of synbiotics in the treatment of AD. It was found that the use of synbiotics in adults and children over the age of 1 year old (when used for at least 8 weeks) had a significant effect on a measure of AD severity. [Chang]
What are synbiotics?
These are a combination of prebiotics and probiotics. Prebiotics are foods or substances that support the growth of beneficial microbes. One major type of prebiotics are fiber-rich vegetables. (Good bacteria and other microbes thrive when they're given lots of fiber to eat.) Probiotics are live microbes (in foods or supplements) which have positive health effects. In this study, the best probiotics were those that contained mixed strains of bacteria, and not just a single strain of bacteria.
How does this translate to dietary recommendations? This post reviews prebiotics in more detail, while this post reviews probiotics in more detail.
The bottom line? For skin health, you have to think about your gut health.
Chang YS, Trivedi MK, Jha A, Lin YF, Dimaano L, Garcia-Romero MT. Synbiotics for prevention and treatment of atopic dermatitis: a meta-analysis of randomized clinical trials. JAMA Pediatr. 2016;170(3):236–42.
Hemarajata P, Versalovic J. Effects of probiotics on gut microbiota: mechanisms of intestinal immunomodulation and neuromodulation. Ther Adv Gastro 2013;6(1):39–51.
Turnbaugh PJ, Ridaura VK, Faith JJ, Rey FE, Knight R, Gordon JI.The effect of diet on the human gut microbiome: a metagenomic analysis in humanized gnotobiotic mice.Sci Transl Med. 2009 Nov 11;1(6):6-14.
Picardo, M., & Ottaviani, M. (2014). Skin Microbiome and Skin Disease The Example of Rosacea, 48(December), 85–86.
Dr. Rajani Katta is the author of Glow: The Dermatologist's Guide to a Whole Foods Younger Skin Diet. To receive future updates on preventive dermatology and the role of diet, sign up here.