As a nutrition expert people always ask me about the gut microbiome. Common questions are what is it, how does it impact our health, and how can we change our gut microbiome to improve our overall health and wellbeing.
First what is the gut microbiome? It contains over 30 trillion microorganisms that live all the way through our gastrointestinal tract (GI) from our mouth all the way to our anus. It includes bacteria, viruses, yeast, and fungi and the types and amounts differ across each area of our GI tract. For example, the microbial composition in our oral cavity is very different from those living in our large intestine – which is what the remainder of this blog will highlight.
Figure 1. Microbial populations across the GI tract. Credit: Ruan W et al., 2020 Dig Dis Sci
The microbiome accounts for about 1 to 3% of our total body weight and it's involved in many different types of metabolic pathways from breaking down nutrients that we ingest via digestion, it allows for the production of certain vitamins (e.g., Vitamin K) and metabolites like short chain fatty acids (SCFA). The microbiome is also involved in the proper function and maintenance of our immune and nervous system.
The gut microbiome composition and function can be attributed to several entities. First we have mode of delivery – meaning, were you delivered via cesarean section or vaginal delivery. Genetics, you have where you lived and currently live, drug use and smoking habits, exercise, your circadian rhythm, stress all contribute; however, diet is one of the largest most influential aspect that shapes the microbiome. The gut microbiome also changes as we age so what the microbiome “looked like” during infancy is certainly not going to look the same at 80 years of age. For this reason, it is necessary to maximize the potential of having a beneficial microbiome composition during ageing. The key to living a long, healthy life is to ensure the beneficial microbes outweigh the pathogenic or toxic microbes, which can be achieved through diet.
Figure 2. What influences our microbiome? Credit: Feng W et al., 2020 Theranostics
Many human disorders are linked to the gut microbiome - everything from neurological diseases, including MS, anxiety, depression, stress, addiction, liver disease, obesity, cardiovascular diseases, diabetes and prediabetes, and insulin resistance. The pathogenic microbes produce pro-inflammatory responses that can lead to allergies, eczema, arthritis, and autoimmune disorders.
A study published in 2017 examined how high animal diet + low plant-based diet changes the gut microbiome. A high animal protein diet is rich in L-carnitine, phosphatidylcholine or lecithin, and especially choline. The pathogenic bacteria convert choline into pro-inflammatory trimethylamine (TMA), which in turn is converted into trimethylamine N-oxide (TMAO) in the liver that is taken up into the blood supply. TMAO leads to many inflammatory processes, forms plaques and platelet aggregation, which can narrow the arteries directly lead to increased risk of developing cardiovascular disease.
Figure 3. How animal-based diets lead to chronic disease risk factors through the microbiome. Credit: Rahman et al., 2017 Frontiers
Furthermore, a study published in Circulation found a positive relationship between blood TMAO concentrations in adults consuming an omnivore (animal-based) diet vs. vegetarian (plant-based) diet. TMAO is also linked to “leaky gut” which can cause pathogenic microbes to translocate from the gut to the blood supply, which is also linked to several diseased conditions. Correspondingly, these diseased conditions have microbiome profiles that are low SCFA, especially butyrate, producers. Butyrate is necessary for maintaining the lining of the gut to prevent bacterial translocation.
Figure 4. How animal-based diets impact TMAO. Credit: Zhu W et al., 2017 Circulation
How do we change our pathogenic microbes to beneficial microbes? Eating a high-fiber, high-resistant starch (prebiotic) diet is necessary to increase the viability and abundance of beneficial gut bacteria. Foods like beans, legumes, and peas, whole grains and cereals, cooked then chilled potatoes, vegetables, fruit, plus nuts and seeds, are all fiber-containing foods that promote gut health. The fiber recommendations include at least 25 g/d for women and 38 g/d for men; however, studies have shown that consuming 40-45 g of fiber per day elicits the most beneficial outcomes for our gut health and staving off chronic diseases.
Figure 5: Fiber regulates bodily processes through the gut microbiome. Credit: Martinez T et al., 2021 Nutrients
Bottom line: eat more plants; eat more fiber; eat more resistant starch. For more information please visit my YouTube channel @drmindypatterson for more information on the intersection of nutrition and health.