Nutritional Modulation of the Gut Microbiome

Nutritional Modulation of the Gut Microbiome

• The gut microbiome contains 10 times the number of microbial cells as the human body.
• Approximately 100 trillion microbes live in the human gut.
• Roughly 5000 different species of microbes live in the gut.
• The gut microbiome weighs approximately 2 kilograms.
• The gut microbiome is composed of bacteria, viruses, fungi, and parasites.
• Major bacterial species in the gut include Prevotella, Ruminococcus, Bacteroidetes, and Firmicutes.

Learning Objectives

• Students will learn about the gut microbiota overview.
• Students will learn about different dietary styles (Western, plant-based, high-fat, medical ketogenic, and Mediterranean).
• Students will learn about the effect of each diet on the gut microbiota.
• Students will learn about fiber and the gut microbiome.
• Students will learn about the effects of bacterial metabolites on inflammation and metabolic endotoxemia.

The Human Microbiome

• 25 phyla are known.
• ~2,000 genera are known.
• ~5,000 species are known.
• ~80% of the metagenome is mappable.
• ~316 million genes are known.
• ~20% of microbial genomes remain unknown.
• ~40% of functional genes are yet to be matched with existing databases.

Geographical Location and Phylum Abundance

• Phylum abundance varies across different geographical regions.
• Firmicutes are the most prevalent phylum (51.1%).
• Bacteroidetes constitute a significant portion (36.0%).
• Other phyla are present in lesser amounts.

Bacteria Ratio

• The ratio between Bacteroidetes and Firmicutes is vital to human health and disease.

Importance of the Gut Microbiome

• Gut bacteria are central to harvesting energy from food, maintaining beneficial/harmful bacteria balance, and producing essential neurotransmitters, enzymes, and vitamins.
• Vitamin K, for example, is produced by bacteria and plays a role in immune and metabolic functions.
• Imbalances in gut bacterial species might lead to disease.

Diet Effect on Gut Bacterial Composition

• Diet is a major factor in altering gut bacterial composition.
• Diet changes may lead to changes in the ratio of bacterial species important to health.
• Diet plays a role in influencing conditions like obesity and type II diabetes. (Western diets are linked to inflammation and obesity)

Beneficial and Harmful Bacterial Species

• A high-animal protein diet often increases harmful bacteria (Bacteroides, Alistipes, Bilophila).
• Beneficial bacteria (e.g., Lactobacillus, Roseburia, E. rectale) are often decreased with this type of diet.
• Changes in these species can affect gut microbiome diversity.

Effect of Animal-Based Diets

• Western diets (high fat, high sugar) are linked to chronic low-grade inflammation, metabolic issues, and obesity.

Effect of Plant-Based Diets

• Low-fat, high-fiber diets can positively alter the microbial composition of the gut.
• They can support beneficial bacteria (e.g., Prevotella and Bacteroides).
• Plant-based diets can reduce Firmicutes.

European vs. African Diet Study

• A study comparing European and African children revealed differences in microbiome composition.
• European children had lower fiber consumption and a different gut microbiome composition compared to African children.

Effect of Gut Microbiome on Health

• The gut microbiome can have a positive or negative impact on health. (high versus low inflammatory bacteria)
• Specific diets might increase or decrease the occurrence of inflammatory bacteria.

Fiber and the Gut Microbiome

• Dietary fiber includes non-digestible carbs and lignin.
• Fiber types differ in chemical structure, solubility, viscosity, and fermentability.
• Soluble fiber is metabolized by gut bacteria, forming short-chain fatty acids (SCFAs).
• Insoluble fiber helps maintain gut health.

Fiber Effect on the Gut Microbiome

• Firmicutes and Actinobacteria are the main responders to dietary fiber.
• High-fiber diets encourage the production of SCFAs.
• Reduced dietary fiber can hinder SCFA production, reducing beneficial effects on gut health.

Prebiotic Inulin

• Inulin-type fructans influence the gut microbiome in individuals with type II diabetes.
• The beneficial effect of these fructans involves increases in Bifidobacteria and SCFA production.
• Inulin-type fructans can cause changes in the intestinal microbial composition.

Resistant Starch

• Resistant starch positively impacts gut microbiota.
• Resistant starch increases Bifidobacterium and other beneficial bacterial species.
• Resistant starch increases SCFA production.

Phytochemicals and Gut Microbiome

• Polyphenols are found in various plants and affect the microbiome positively.
• Flavonoids are found in fruits and vegetables; they exhibit gut-modulating effects, like reducing LPS and increasing SCFA production.
• Specific polyphenols are linked to anti-cancer properties.

Bacterial Metabolites

• Bacterial metabolites of different origins can influence inflammation and metabolic endotoxemia.
• Includes SCFAs, bile acids, tryptophan, and trimethylamine.

Short-Chain Fatty Acids (SCFAs)

• SCFAs are produced by bacterial fermentation of dietary fiber.
• SCFAs can improve weight loss, enhance glycemic control, and promote better metabolic health.
• SCFAs can have significant effects on the gut microbiome, reducing inflammation, improving insulin resistance, and influencing satiety.

Bile Acids

• Bile acids are secreted into the gut in the presence of fat.
• Primary bile acids (cholic acid and chenodeoxycholic acid) are transformed by gut microbiota.

Tryptophan

• Indole derivatives and tryptamine form through tryptophan metabolism, influencing epithelial and immune cells.
• Tryptophan metabolites can reduce inflammation and reprogram Treg cells.

Trimethylamine (TMA/TMAO)

• TMA is a byproduct of the breakdown of red meat and processed food components.
• TMA is converted to TMAO, which is linked to inflammation, type II diabetes, and obesity.

Summary

• Diet significantly influences bacterial composition in the gut.
• Shifts in beneficial bacteria (e.g., Prevotella and Bacteroides) are associated with obesity and diets high in fat and sugar, low in fiber.
• Plant-based diets can have beneficial effects on the gut microbiome and overall health, potentially reducing inflammation, improving insulin sensitivity, and promoting satiety.
• Mediterranean-type diets are linked to positive changes in gut microbiome composition and production of beneficial metabolites.