Posted on by Joy Y. Erdile, MSc, RD

Negative Effect of Dietary Carbohydrate on the Gut Microbiome in IBD

Introduction

Several recent studies have found a relationship between the species of bacteria and fungi that live in our large intestine, carbohydrate intake, and Irritable Bowel Disease (IBD), including Ulcerative Colitis and Crohn’s disease. This article elaborates on how this knowledge may help improve symptoms for those with IBD.

The Gut Microbiome & Mycobiome

The trillions of gut bacteria that live in our intestines are collectively referred to as the “gut microbiome,” along with fungi (called the “mycobiome”) and archaea. We are in a symbiotic relationship with these organisms—what we eat feeds them, and in turn, they produce helpful by-products like short chain fatty acids (SCFA) [1]. These SCFA play an important role in maintaining blood sugar, fat metabolism, and even appetite regulation [1].

Simple Sugars: Monosaccharides & Disaccharides

Monosaccharides include glucose, fructose and galactose. Disaccharides are pairs of these, such as sucrose (table sugar), lactose (milk sugar), and maltose.

Complex Carbohydrates: Strings of Sugar Molecules

Complex carbohydrates are larger molecules. Oligosaccharides are found in dried beans and lentils; they cannot be broken down by human enzymes but are fermented by gut bacteria [2]. Polysaccharides, including Starch, are long chains of glucose. While some starches are digested easily, they quickly affect blood sugar and are easily fermented by the gut microbiome, potentially playing a role in colitis for genetically susceptible individuals.

How Simple Sugars Can Induce Colitis

A study published in late 2020 documented how simple sugars in the diet can induce colitis [2]. Researchers found that feeding mice simple sugars like glucose, fructose, and sucrose damaged the protective mucus layer of the colon and increased harmful bacteria that break down this lining.

Mice fed a glucose solution suffered from aggressive colitis, bloody diarrhea, and rapid loss of nearly 20% of their body weight. Their colons were shorter, showing loss of epithelial crypts, inflammation, and ulceration.

In mice genetically susceptible to colitis, 90% developed the disease when treated with glucose. These mice experienced much greater loss of body weight and higher diarrhea and rectal bleeding. Colon tissues showed increased inflammation and a higher expression of inflammatory molecules [2].

Of Mice and Men

While results in animal studies aren’t always directly applicable to humans, mice and humans share virtually the same set of genes [3]. This study provides a strong indication of how sugar might impact the human gut lining.

Therapeutic Diets: Low-FODMAP and Low-Carb

For those with IBD, a low-FODMAP diet is often used to reduce symptoms. FODMAP stands for fermentable, oligo-, di-, monosaccharides and polyols. Reducing these fermentable sugars often provides significant relief. I have often wondered if the effectiveness of low-FODMAP is due to its overall low-carbohydrate content.

Ketogenic Diets and the Gut Mycobiome

A pilot study looked at how a Mediterranean ketogenic diet (very low in carbs, usually <20g/day) could decrease certain gut fungi [4]. Researchers found a significant reduction in Candida species during the ketogenic phase. This is important because the genus Candida is implicated in various gut-related diseases including inflammatory bowel diseases, Crohn’s disease, ulcerative colitis, and gut inflammation.

The study suggested that a ketogenic diet increases the short-chain fatty acid butyrate, which inhibits the growth of strains of Candida. This implies a therapeutic role for a Mediterranean ketogenic diet in managing IBD symptoms.

Final Thoughts

In light of these studies, it makes sense for those with IBD or at genetic risk to reduce simple sugars like glucose, fructose, and sucrose. Adoption of a Mediterranean Ketogenic Diet may also help reduce Candida overgrowth, improving long-term gut health.

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Joy

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References

  1. Morrison DJ, Preston T. Formation of short chain fatty acids by the gut microbiota and their impact on human metabolism. Gut Microbes. 2016;7(3):189-200. [https://pubmed.ncbi.nlm.nih.gov/26963409/]
  2. Khan S, Waliullah S, Godfrey V, et al. Dietary simple sugars alter microbial ecology in the gut and promote colitis in mice. Sci Transl Med. 2020 Oct 28;12(567):eaay6218. [https://doi.org/10.1126/scitranslmed.aay6218]
  3. National Human Genome Research Institute. Background on Comparative Genomics. Genome.gov. 2020. [https://www.genome.gov/about-genomics/fact-sheets/Comparative-Genomics-Fact-Sheet]
  4. Nagpal R, Neth B, Wang S, et al. Gut mycobiome and its interaction with diet, gut bacteria and Alzheimer’s disease markers in subjects with mild cognitive impairment: A pilot study. EBioMedicine. 2020 Sep;59:102950. [https://doi.org/10.1016/j.ebiom.2020.102950]
 
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