In the human body, the population of microorganisms vastly outnumbers human cells, with the ratio being approximately 10 microorganisms for every single human cell. It's no surprise that the microbiomes inhabiting our gut and skin profoundly impact our health. The gut microbiome alone is involved in various essential tasks, from aiding digestion and synthesizing vital nutrients to modulating the immune response and even influencing our mental health. Among its many influences, an area that's recently gained attention is the relationship between gut health and skin health, the largest organ in the body.

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What is The Gut Microbiome?

A thriving community of trillions of microorganisms, including bacteria, viruses, protozoa, and fungi, form the gut microbiome within our gastrointestinal tract, primarily in the small and large intestines. These diverse residents establish a mostly symbiotic relationship with the body, benefiting both parties. Still, a fraction of potentially harmful microbes also coexist, and when the balance between them is disturbed, it may lead to an increased susceptibility to diseases.

The gut microbiome plays multiple roles in the body's overall health, from breaking down complex food substances to stimulating the immune system and synthesizing essential vitamins and amino acids, including the B vitamins and vitamin K. It facilitates the breakdown of fibers and starches in the large intestine, which leads to the creation of short-chain fatty acids (SCFAs), which not only serve as a nutrient source but also contribute to various physiological processes.

Interestingly, each person's gut microbiota network is unique, initially determined by DNA and later influenced by environmental exposures and diet. This network even provides a defense against harmful organisms entering the body through contaminated food or water. So, it's worth noting that our understanding of the gut microbiome is vital for a comprehensive grasp of human health (2,3).

What is The Skin Microbiome?

The skin microbiome refers to a diverse microorganism network encompassing bacteria, fungi, viruses, and mites, inhabiting our skin, our body's largest organ. This network spans unique ecological niches across the skin's vast area (around 25 m²) with varied climates due to differences in temperature, humidity, and sebaceous gland densities.

Distinct bacterial groups thrive in different skin types: Staphylococcus and Corynebacterium in moist areas, Cutibacterium in oily parts, with the highest diversity found in dry regions. Notably, Malassezia spp. comprises the majority of the fungal flora. The microbiome also includes mites and specific human papillomaviruses (6).

Formation of the skin microbiome begins at birth, influenced by various internal and external factors throughout life. Crucially, it helps maintain skin balance, safeguards against harmful invaders, and modulates immune responses. However, any disturbance leading to microbial imbalance, or dysbiosis, might contribute to skin disorders like dermatitis and acne (6).

What is The Gut’s Role in Overall Skin Health?

The gut and skin are home to diverse microbiomes that work in harmony to maintain overall health. Dysbiosis, an imbalance in these microbiomes, along with food sensitivities can disrupt this harmony, leading to inflammation and a wide array of skin disorders such as atopic dermatitis, psoriasis, acne vulgaris, and even skin cancer. The imbalance can be caused by diet, hygiene, and genetic factors, often resulting in an altered immune response.

Notably, the gut plays a key role in metabolizing and absorbing essential micronutrients, impacting skin health. For instance, gut bacteria breakdown indigestible complex polysaccharides into essential nutrients like vitamin K and B12, butyrate, and propionate, which positively affect epithelial barrier integrity. However, certain diets, like the Western diet, can lead to gut dysbiosis, affecting immune responses and potentially leading to skin disorders. Consumption of food components like glycoalkaloids, alpha tomatine, capsaicin, and gluten, which are known to impair the intestinal barrier, can cause gut bacteria to enter the bloodstream, leading to skin pathologies (8).

Interestingly, the gut-skin axis is not unidirectional. Skin exposure to UVB, for instance, indirectly increases gut microbiome diversity by affecting serum vitamin D levels. In conditions where the intestinal barrier is compromised, often referred to as a "leaky gut," bacteria can infiltrate the bloodstream, potentially causing inflammation and other systemic issues. This could, in turn, impact skin health (8).

How to Test Gut Health in Your Patients

These tests, in combination with a careful clinical evaluation, can give healthcare providers a more complete picture of their patients' gut health.

Comprehensive Stool Testing

The Diagnostic Solutions GI-MAP Zonulin Test is a comprehensive stool analysis that aims to identify gut dysbiosis, inflammation, and intestinal permeability, commonly known as "leaky gut". It tests for zonulin, a protein that modulates permeability in the gut lining. Elevated zonulin levels are a marker for compromised gut barrier function, making this test a valuable tool for diagnosing leaky gut syndrome. Importantly, it also investigates markers of digestion and absorption, pathogenic and commensal bacteria, yeasts, and parasites, hence providing a comprehensive view of gut microbiome health. It is helpful for identifying imbalances in the gut microbiota, known as dysbiosis, which may be linked to many health conditions, ranging from gastrointestinal symptoms to skin conditions.  

Food Sensitivity Testing

The Alletess 96 IgA Food Sensitivity Panel is a blood test designed to identify IgA-mediated food sensitivities, which can influence gut health. The test evaluates the immune response to 96 different foods by quantifying the level of IgA antibodies. IgA antibodies, a type of immunoglobulin found predominantly in mucosal areas like the gut, and plays a vital role in the immune system's response to perceived threats. When IgA antibodies react to certain foods, it may indicate a food sensitivity, which can lead to inflammation and potentially disrupt the gut barrier function. This test helps clinicians uncover which foods might be causing a patient's adverse reactions, providing information for guiding dietary interventions.

Functional Medicine Labs That Can Help Individualize Treatment for Patients' Skin Health

Functional medicine labs offer a variety of tests that can help tailor treatment to patients, allowing providers to optimize management strategies.

Micronutrient Testing for Gut and Skin Health

The SpectraCell Micronutrient Test is a comprehensive blood test that measures the function of 31 vitamins, minerals, amino acids, and antioxidants within the patient's cells. Nutrient deficiencies can have profound implications on skin health. The gut plays a crucial role in nutrient absorption, so dysbiosis, inflammation, or impaired barrier function can result in suboptimal nutrient uptake, adversely affecting skin health. Moreover, certain micronutrients like zinc and other vitamins are directly involved in skin regeneration and collagen synthesis, making their optimal levels critical for maintaining skin integrity and appearance.

Organic Acids Testing for Gut and Skin Health

The Mosaic Diagnostics Organic Acids Test is a comprehensive metabolic panel that measures levels of organic acids - metabolites resulting from the body's cellular processes - in urine. These compounds can indicate the efficiency of various metabolic pathways, including those influenced by gut microbiota, such as the breakdown of dietary components into short-chain fatty acids (SCFAs). SCFAs, especially butyrate, are crucial for maintaining gut barrier integrity and modulating systemic inflammation, factors that impact skin health. Dysbiosis can disrupt these processes, leading to metabolic imbalances potentially reflected in the OAT results.

Inflammation Testing for Gut and Skin Health

The BioReference C-Reactive Protein (CRP) Test is a blood test that measures levels of CRP, a protein made by the liver as a response to inflammation in the body. High CRP levels suggest systemic inflammation, which can be triggered by various factors, including gut dysbiosis or a 'leaky gut'. When gut barrier function is compromised, bacteria and their toxins can enter the bloodstream, inciting an inflammatory response. This systemic inflammation may manifest in the skin, exacerbating conditions like acne, psoriasis, or eczema. Regular monitoring of CRP levels helps healthcare providers assess the effectiveness of gut-targeted interventions in mitigating inflammation and improving skin health.

Integrative Nutrition For Gut Health and Skin Health

To manage and potentially prevent these skin conditions, dietary modification to improve the gut is emerging as an effective intervention. The Microbiome Diet, for instance, adopts a three-phase approach centered on the restoration of gut health. Phase one, known as the 'elimination diet,' removes foods that interfere with the gut microbiome's equilibrium. Concurrently, it introduces foods rich in prebiotic and probiotic elements and fermented foods, which enhance the health of the gut microbiome.

Complementing this approach is the Elimination Diet, a methodology pioneered in functional medicine to identify food sensitivities. It works on the principle of exclusion and gradual reintroduction of suspect foods, which helps pinpoint foods causing potential adverse reactions. It’s worth noting that the Elimination Diet is not designed as a long-term lifestyle change but a temporary measure to identify triggers and then reintroduce a diverse range of foods back into the diet. This process involves two main phases: an elimination phase lasting around 30 days, followed by a reintroduction phase. During the elimination phase, suspected foods are avoided entirely, while the reintroduction phase involves slowly adding these foods back into the diet and observing any adverse reactions.

Specific dietary components, such as gluten, also deserve consideration when talking about gut and skin health. A non-celiac individual with skin manifestations like psoriasis, atopic dermatitis, vitiligo, or palmoplantar pustulosis, may benefit from a gluten-free diet.

Moreover, an anti-inflammatory diet rich in healthy fats and antioxidants may be a good choice for individuals dealing with chronic inflammatory skin conditions. It’s worth noting that in cases where testing identifies leaky gut syndrome, focusing on repairing the gut is paramount. A compromised gut barrier can contribute to systemic inflammation, potentially exacerbating skin conditions (26).

Supplements and Herbs For Gut Health and Skin Health

For patients interested in supplements and herbs, probiotics, zinc, l-glutamine, and vitamin A are evidence-based solutions that may help reduce symptomatology.

Probiotics For Gut Health and Skin Health

Cultivating gut well-being in individuals of all ages through probiotics can have positive implications for skin health. This results from their capacity to lessen inflammation and strengthen the immune system. A harmonious gut environment aids in managing inflammation and boosting the body's protective responses, which are integral to the overall wellness and rejuvenation of the skin. Incorporating probiotics into one's diet can be valuable in managing various skin conditions and enhancing the body's immunological functions. Two types of strains that have been specifically studied for this purpose are Bifidobacterium and Lactobacillus (31,32,33).

Dose: 10 to 20 billion colony-forming units (CFUs) per day for adults

Duration: Ongoing

Zinc for Skin and Gut Health

Zinc plays a fundamental role in maintaining overall skin and gut health, highlighting the need for adequate intake. Its importance is especially seen in skin renewal processes and wound healing, where it works by supporting various zinc-dependent proteins and enzymes. Similarly, zinc's role in gut health is critical, with the right balance necessary for the maintenance of the intestinal barrier and healthy gut microbiome. Consequently, both too much and too little zinc can disrupt gut health, causing issues like diarrhea and inflammation (36,37).

Dose: Up to 40-50 mg per day

Duration: Ongoing

L-Glutamine for Skin and Gut Health

L-Glutamine, an abundant amino acid in our body, plays a pivotal role not only in muscle development but also in supporting gut and skin health. Its significant influence on gut health involves balancing gut microbiota, fortifying the intestinal lining, and reducing inflammation. Additionally, it assists in gut-brain communication through neurotransmitter synthesis. In terms of skin health, continuous intake of L-glutamine, along with other essential amino acids, has been linked to improvements in muscle mass and skin texture (39,40).

Dose: between 15-30 grams

Duration: At least 14 days. (The lifespan of cells in the intestinal lining is quite short, as they typically renew themselves approximately every five days.)

Vitamin A for Gut and Skin Health

Vitamin A is vital to our overall health, particularly in maintaining gut and skin health. It enhances the resistance of our digestive system to infections and other potential damages. This is achieved by managing the intestinal lining and mucosal immune cells and modulating proteins critical for intestinal barrier function. Furthermore, Vitamin A is integral in skin health, supporting the daily rejuvenation of skin cells and ensuring that tissues, including skin and various organ linings, produce adequate mucus to serve as a protective barrier against infections (41,42).

Dose: 7,500-15,000 µg RAE (as retinyl palmitate) per day

Duration: Ongoing or at least one year

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Summary

The connection between gut microbiome and skin health is a burgeoning area of research. Maintaining a healthy gut microbiome can have far-reaching effects on our overall health, including our skin's health. Whether it's through personalized testing, diet, or supplementation, functional medicine approaches can offer valuable tools for maintaining a healthy gut and, consequently, healthy skin. As we continue to learn about the gut-skin axis, we can look forward to more targeted and effective strategies for promoting skin health.