Gut Microbiome

Question 1

Define microbiome.

Answer 1

The collection of genomes from all the microorganisms found in a particular environment (e.g., in the gut).

Question 2

Define: microbiota.

Answer 2

Refers to all the microorganisms, including bacteria, viruses, and fungi, that are found within a specific environment (e.g., in the gut)

Question 3

What is the gut microbiota?

Answer 3

• Microbes in the intestine
• Trillions of microorganisms helping to break down otherwise indigestible foods.
• Suggested to influence human health

Question 4

What are the two groups of beneficial bacterial phyla dominant in the gut?

Answer 4

• Bacteroidetes
• Firmicutes

Question 5

The relative proportion of Bacteroidetes is […] in obese people in comparison to lean people.

Answer 5

The relative proportion of Bacteroidetes is decreased in obese people in comparison to lean people.

This proportion increases with weight loss.

Question 6

Compare the gut microbiota of obese versus lean individuals.

Answer 6

Question 7

Describe the change in gut microbiota in 12 obese individuals on a calorie restricted diet.

Answer 7

Question 8

What does a gut microbiota transplant from an obese donor do to mice?

Answer 8

• Leads to increased adiposity

However, this weight gain can be prevented by co-housing the mice! Co-housing mixes the microbes!

Question 9

Describe the key points of gut microbiota transplant experiments in mice.

Answer 9

• Lean phenotype associated with greater diversity in microbes - more Bacteroidetes
• Adding ‘obese microbes’ to mice transplanted with ‘lean microbes’ does not lead to obesity
• BUT adding ‘lean microbes’ to mice transplanted with ‘obese microbes’ DOES prevent weight gain

Question 10

Describe how altering the gut microbiota may have implications for prevention/treatment of obesity and insulin resistance in humans.

Answer 10

• Transplant with microbes from ‘lean donors’ led to improved insulin sensitivity in some subjects

Question 11

What are the potential mechanisms by which the microbiota composition may influence adiposity, inflammation, and glucose or lipid homeostasis? [4]

Answer 11

• Harvesting of unabsorbed food
• Interactions with immune response in the gut
• May influence hormones involved in appetite and metabolic regulation
• Produces metabolites and microbial products like SCFAs, secondary bile acids, and lipopolysaccharides

Data are accumulating on how the gut microbiota significantly affects the bidirectional communication between the GI tract and the brain.

Question 12

What types of foods are substrates for gut bacteria to produce SCFAs?

Answer 12

Fermentable fibers

Question 13

What are prebiotics?

Answer 13

Indigestible fibers that may promote growth of certain gut bacteria species

Question 14

What are probiotics?

Answer 14

Live microbes that may alter the gut microbiota

Question 15

What are the benefits to low-fermentable fiber?

Answer 15

• Low-fermentable fiber supplementation following oral FMT (fecal microbiota transplantation) improved insulin sensitivity from baseline to 6 weeks in patients with severe obesity and metabolic syndrome

Question 16

What is HOMA2?

Answer 16

• The Homeostasis Model Assessment (HOMA) estimates steady state beta cell function (%B) and insulin sensitivity (%S), as percentages of a normal reference population.
• The HOMA 2 (Homeostasis Model Assessment) calculator is a tool used to express the degree of insulin sensitivity (IS) and insulin resistance (IR) in the patient from the following biomarkers: Fasting Blood Glucose, Fasting Insulin and/or C-Peptide

Question 17

What is murine methyl donor deficiency?

Answer 17

• MDD diets with or without succinylsulfathiazole (antibiotic that inhibits growth of folate-producing gut bacteria) were administered to pregnant dams
• MDD pups were markedly underweight relative to pups from control diet group.

Question 18

Why are MDD diets significant?

Answer 18

• MDD and succinylsulfathiazole decrease intestinal microbiota communitiy diversity
• Diversity was greater in control mice than in MDD mice.

Question 19

What are the take-home messages regarding microbiota that Dr. Stefanska has for us?

Answer 19

• The composition of the gut microbiota may influence metabolism and inflammation and chronic diseases, such as obesity and diabetes
• Altering the gut microbiota through pre/pro-biotics and other dietary approaches may have implications for prevention of metabolic disorders
• Development of obesity, diabetes or related metabolic disorders is a complex, multifactorial process, involving genetics, nutrition, and other behavioral, lifestyle and environmental factors