You’re outnumbered. Your 30 trillion human cells, to their 100 trillion. We’re talking microbiome. And, did you know that you are more bacteria than you are human? Your body is home to roughly 40 trillion bacterial cells alone.1 We are used to thinking of bacteria, fungus, and viruses as invaders, but these microbial colonies are at the forefront of research demonstrating the power that the human microbiota has on both our mental and physical health.

Earlier this year, a meta-analysis of 21 different studies, released its findings showing that regulating intestinal microbiota (either through diet or implementing probiotics) had a positive effect on anxiety in 52% of studies. However, the studies that implemented diet changes (rather than probiotics) showed an 86% effectiveness.2 In fact, researchers and microbiologists all over the world are making connections between our gut microbiomes and depression. Jeron Raes, a microbiologist in Belgium found that two specific microbes were missing in depressed subjects. One specifically, Coprococcus, seems to have a key pathway related to dopamine (a neurotransmitter known to be connected to depression).3

So, what is the human microbiota? Composed of archaea, bacteria, bacteriophage, fungi, protozoa, and viruses,4 the human microbiome lives on skin, eyes, nose, throat, mouth, lungs, and gastrointestinal tract. Over 99% of our human microbiome resides in our intestines and is composed of over 1,000 known species of bacteria,5 each of which plays unique roles. Estimated to weigh between two and five pounds or roughly the size of your brain, the human microbiome works together to function as an extra organ.

The human microbiome plays a part in a variety of crucial functions including: stimulation of our immune system, inhibition of pathogens, gastrointestinal tract motility (movement), nutrient absorption and the synthesis of specific vitamins and short-chain fatty acids, the metabolism of compounds and drugs (referred to as pharmacokinetics), as well as cardiovascular and brain health. Many researchers are now considering that this microbial organ may even rival the liver in the number of functions it performs.6

But, a landslide of emerging research is now linking our biomes not only to many digestive disorders but also to a surprising number of other health concerns:
Research is linking the gut biome and an imbalance thereof, to mood and behavior.7 This new research is so compelling for common disorders, such as low serotonin levels, that it’s almost malpractice to prescribe Selective Serotonin Reuptake Inhibitor (SSRI) drugs to a patient without first asking about their diet or gut health. Over 90% of serotonin, the neurotransmitter responsible for proper brain function, is produced in the digestive tract – meaning serotonin is heavily influenced by the balance of gut biome.

Today researchers are attempting to piece together why an imbalance occurs, including what shapes our human microbiome.8 The imbalance of our gut microbial community is referred to as dysbiosis. And we do know that dysbiosis can occur for a variety of reasons including: 
  • Alcohol consumption
  • Chemical consumption
  • Medications
  • Antibiotics
  • Unprotected sex
  • High levels of stress or anxiety
  • FODMAPs
  • High levels of sugar, or additive consumption
  • Poor dental hygiene
  • Radiation
In fact, one study9 noted a 20-30 percent rise in the Bacteroides Fragilis subspecies Thetaiotaomicron in the stool samples of study participants just in response to fear and anger. Growth of this bacteria is enhanced by bile and we know that stress increases the production of epinephrine which inhibits gastric motility (movement) and bile flow.10 Thetaiotaomicron is part of the normal human gut microbiota, however dysbiosis can cause opportunistic infections.11We are seeing a variety of studies demonstrating the massive impact that antibiotics, stress, and diet can have on gut flora.12

As mentioned in the above meta-analysis study, one of the biggest components of gut dysbiosis is our modern diet. And one new approach, the FODMAP diet, is showing promise in alleviating symptoms from a variety of digestive disorders. Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols, are short chain carbohydrates that are resistant to digestion. When they reach the large intestine, these foods draw in water and begin to ferment causing, bloating, pain, gas, and diarrhea. However, it is important to note, that while reducing FODMAPs is shown to alleviate many GI symptoms and alter gut flora, it is important to consult a doctor and/or nutritionist before making significant dietary changes.

Other gut dysbiosis culprits? Diets high in simple sugars.13 Which makes sense because sugar feeds bacteria.14 But also, according to a Washington University School of Medicine study, sugar decreases the growth of a protein that fosters healthy gut colonization.15 In fact, one 2017 study shows how gut bacteria communicate with the brain and can actually alter cravings.16 All those late night cravings for sugar starting to ring a bell? Today we are seeing a collective desire for greater health and wellness, especially in our gut. One example called the Microbiome Diet17 is a trendy new diet geared towards just that. And phase one of this diet actually eliminates many of the high FODMAP foods we cover in our recent FODMAP article here. A good rule of thumb? Most healthy balanced diets place an emphasis on organic vegetables considering fiber intake carefully, sticking to occasional fruits to satisfy your sweet tooth, eating humanely raised protein in moderation, healthy fat sources, incorporating prebiotic and probiotic foods, and avoiding additives, chemicals, GMO’s and pesticides. And most importantly, limiting processed foods. When it comes to making good food choices, we recommend always trusting your gut.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4991899/

[2] https://www.sciencedaily.com/releases/2019/05/190520190110.htm

[3] https://www.sciencemag.org/news/2019/02/evidence-mounts-gut-bacteria-can-influence-mood-prevent-depression

[4] https://www.ncbi.nlm.nih.gov/pubmed/30062595

[5] https://www.gutmicrobiotaforhealth.com/en/about-gut-microbiota-info/

[6] http://www.altmedrev.com/archive/publications/9/2/180.pdf

[7] https://www.gastrojournal.org/article/S0016-5085(11)00607-X/fulltext

[8] https://phys.org/news/2019-10-furthers-human-gut-microbiome.html

[9] Holdeman LV, Good IJ, Moore WE. Human fecal flora: variation in bacterial composition within individuals and a possible effect of emotional stress. Appl Environ Microbiol 1976;31:359-375

[10] https://www.ncbi.nlm.nih.gov/pubmed/44929

[11] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3462683/

[12] http://www.altmedrev.com/archive/publications/9/2/180.pdf

[13] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6024874/

[14] https://www.pbs.org/wgbh/nova/article/sugar-keeps-good-microbes-at-bay/

[15] https://www.pnas.org/content/116/1/233

[16] https://www.scientificamerican.com/article/how-gut-bacteria-tell-their-hosts-what-to-eat/

[17] https://www.healthline.com/nutrition/microbiome-diet#guidelines