Apr 25 / Star Khechara

The link between gut-health and skin-health

There are 500-100- bacterial species inside each human’s intestinal tract. Another study suggests that number to be 3500. Most gut bacteria are commensal (non-pathogenic) and live in a symbiotic relationship with the host (us! you, me, your clients - we are all hosts).

The gut microbiome is multi-functional and involved in:

  • Nutrient production
  • Nutrient metabolism
  • Structural maintenance of the gut mucous membrane
  • Regulating the immune system and protection against pathogenic bacteria

Gut food

The gut bacteria are happy and thriving when feeding on their primary nutrition source: Carbohydrates.

Fibre and MACs (Microbiota Accessible Carbohydrates) are essential components for healthy gut flora. MACs are diet-derived carbohydrates in the form of non-starch polysaccharides (NSPs), oligosaccharides and resistant starch.

You'll know these as 'prebiotics'.

And guess where you'll find these gut-healthifying carbohydrates? Fruits, vegetables and legumes; the microbiome loves your plant-based meals.
Prebiotics and probiotics that act on the gut-skin axis possess many biological activities, including immunomodulatory and antioxidant activity, which can benefit skin conditions by increasing skin hydration, skin gloss, skin elasticity, and alleviating facial wrinkles.
LIFE (BASEL). 2022.

Skin-health nutrition made by the microbiome

Non-Starch Polysaccharides (NSPs) leave the small intestine intact and are fermented into Short Chain Fatty Acids (SCFAs) by the gut flora in the colon.

  • Short-Chain Fatty Acids from the colon modulate inflammation in the skin.
  • Dietary fibre and SCFAs - particularly Butyrate - help to maintain skin barrier integrity and epidermal thickness
  • The SFCA Butyrate is being studied as an intervention for Eczema.
  • Lysine and Threonine (essential for Collagen biosynthesis) in adult humans is synthesised by the gut bacteria  

Emerging research has shown that an imbalance in the gut microbiome, known as dysbiosis, can lead to systemic inflammation and trigger skin conditions such as acne, eczema, and rosacea.

Gut dysbiosis and skin-ageing

Research shows that the gut microbiome decreases in diversity with age-related deterioration.
Biological age not necessarily chronological age.

  • Dysbiosis leads to premature skin ageing via upregulation of MMPs (Matrix Metalloprotinases) that degrade extracellular matrix proteins including collagen and elastin.
  • Age-associated gut dysbiosis also results in proinflammatory materials passing through the gut wall.

Diet and gut-health

Non-Starch Polysaccharides leave the small intestine intact and are fermented into Short Chain Fatty Acids (SCFAs) by the gut flora in the colon.

20% of circulating Lysine and Threonine (essential for Collagen biosynthesis) in adult humans is synthesised by the gut bacteria  

Intestinal inflammation is measure by the concentrations of a bio-marker called: Lipocalin-2 (Lcn-2) and this biomarker decreases on a plant-based diet

Foods that kill the microbiome

Western-style diet low in MACs and high in:
  • Meat / eggs / dairy
  • Low carb diets
  • Antibiotics
  • Lack of fibre (especially fermentable fibre)
  • Lack of fruit & vegetables
  • Diet high in lectins


Trimethylamine N-oxide is generated by gut bacteria from high levels of Carnitine (from meat and dairy) and choline (meat and eggs). TMAO is also pre-formed in fish. TMAO is a potent inflammatory agent that triggers increased levels of pro-inflammatory cytokines and decreased levels of anti-inflammatory cytokines
Several studies observed that baseline plasma TMAO levels were lower among vegan and vegetarian subjects compared to omnivores
Food Funct., 2020

The (bite-sized) summary

The health of the gut microbiome has an impact on the health of the whole human
The gut makes lipids that are needed for the skin barrier
The gut also makes some of the key amino acids used in collagen biosynthesis
The microbiome thrives on whole-food carbohydrates: fruits and vegetables
A western-style dietary pattern - high in meat, wheat, eggs, dairy and fats - is the worst dietary style for microbiome health.
People who eat a plant-based diet (whether vegan or not) have the healthiest and most diverse microbiome


  • Kumar, Vikas, Amit K. Sinha, Harinder P. S. Makkar, Gudrun de Boeck, and Klaus Becker. "Dietary Roles of Non-Starch Polysachharides in Human Nutrition: A Review." Critical Reviews in Food Science and Nutrition 52.10 (2012): 899-935.
  • Deleu, Sara, Kathleen Machiels, Jeroen Raes, Kristin Verbeke, and SĂ©verine Vermeire. "Short chain fatty acids and its producing organisms: An overlooked therapy for IBD?." EBioMedicine 66 (2021).
  • Trompette, AurĂ©lien, Julie Pernot, Olaf Perdijk, Rayed Ali A. Alqahtani, Jaime Santo Domingo, Dolores Camacho-Muñoz, Nicholas C. Wong, Alexandra C. Kendall, Andreas Wiederkehr, Laurent P. Nicod, Anna Nicolaou, Christophe von Garnier, Niki D. J. Ubags, and Benjamin J. Marsland. "Gut-derived short-chain fatty acids modulate skin barrier integrity by promoting keratinocyte metabolism and differentiation." Mucosal Immunology 15.5 (2022): 908-926. 
  • Ratanapokasatit Y, Laisuan W, Rattananukrom T, Petchlorlian A, Thaipisuttikul I, Sompornrattanaphan M. How Microbiomes Affect Skin Aging: The Updated Evidence and Current Perspectives. Life (Basel). 2022 Jun 22;12(7):936
  • C. SimĂł and  V. GarcĂ­a-Cañas  â€śDietary bioactive ingredients to modulate the gut microbiota-derived metabolite TMAO. New opportunities for functional food development” Food Funct., 2020,11, 6745-6776
  • Sonnenburg, Erica D, and Justin L Sonnenburg. "Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates.." Cell metabolism 20.5 (2015): 779-786.
  • Tomova, Aleksandra, Igor Bukovsky, Emilie Rembert, Willy Yonas, Jihad Alwarith, Neal D. Barnard, and Hana Kahleova. "The Effects of Vegetarian and Vegan Diets on Gut Microbiota." Frontiers in Nutrition 6 (2019).


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Star Khechara

Professional agehacker, author, speaker, founder of skin nutrition institute
About me
Skincare formulator and beauty author turned skin-nutrition educator: Star distilled her 20+ years of skin-health knowledge into the world’s first international accredited skin-nutrition school to teach skin therapists, facialists, face yoga practitioners and estheticians how to help their clients feed the skin from within for cellular-level rejuvenation and vibrant beauty. 
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