All I Want for Christmas Are My Two Front Teeth and More Bacteroidetes!

21 Dec 2017 8:55 AM | Nicole Withee (Administrator)

Thanks to MSU Denver students, Shawn Portwood and Alicia Wildman for contributing this article

The human digestive tract is an amazing organ system, it helps us break down food, absorb nutrients, and provides over 70% of our immune functions and that’s just from the bacteria found in our intestines.1 The bacteria, or biota, located within are so unique, one might even call them our own digestive finger print. So, how can we eat this holiday season to feed these critters and optimize how they work for us?

First a background, there are two major classes of bacteria found in our gastrointestinal tract (GIT). These include Firmicutes and Bacteroidetes, trust me there’s way more but that’s a topic for another day.i, 2  These two classes play very different roles in utilizing the foods we eat, each special in their own ways. So let’s dive in!

Firmicutes get a bad rap in the gut biota. When this phylum of bacteria is in a higher proportional ratio to Bacteroidetes, it has been shown to create a dysbacteriosis of the gut. In other words, if you have too many Firmicutes and your gut colony is out of whack then you have a potentially higher risk for gaining weight. This was demonstrated in a Ukraine study in which stool samples were collected and bacterial content was sequenced. Participants were grouped into categories by BMI and tests revealed the Firmicutes colonized at a higher percentage rate as BMI increased.3 Also, a mouse study that was published in Nature took gene sequencing samples from overweight ob/ob mice and their lean +/+, ob/+ littermates. In a similar breakdown to human biota, ~90% of the bacteria were in the two mentioned phyla – Firmicutes and Bacteroidetes. In the obese mice, there was a 50% higher abundance of the Firmicutes species over Bacteroidetes and the inverse held true in the lean mice. 4

Studies show that once you have established whom the ALPHA bacterial phyla is, which is dictated through early childhood development and dietary intake, how you retain caloric density gets sorted one way or another by the Bacteroidetes or Firmicutes. If Firmicutes tend to be favored in your gut fight club than you have a much higher tendency to retain and absorb broken down fats, carbs and proteins that are turned into Short Chain Fatty Acids (SCFA) to be used as energy. The mechanism at play here is the microbes suppressing the host’s fasting-induced adipocyte factor, and by suppressing this enzymatic reaction more triglycerides end up in adipocytes.6  So, if you have a ton of these overachieving bugs you will retain too much stored energy and doing that for years on end may lead to negative health outcomes such as obesity.  So what foods tend to feed your colony of Firmicutes? There is some research that shows these little bugs thrive in people with a diet that is high in both fats and sugars (The Standard American Diet aka SAD!).  

Foods of plant origin contain fiber, something we simply cannot get from meat, eggs, or milk. The vegetables, fruits, grains, and seeds we eat all contain a variety of fibers. Some are digestible by our own bodies and some are indigestible. For the fibers our bodies cannot break down, we rely on the bacteria in our GIT to lend us a hand. Bacteroidetes have the special ability to break down glycans or huge links of carbs that we would not otherwise be able to use. The indigestible fiber we get from our diet not only feed these bacteria and keeps them in working order, but the by-products of this breakdown feed the cells in our GIT and keep our digestion in working order.ii This phyla is also known to produce SCFA but to a lesser degree than that of the Firmicutes. For this reason, Bacteroidetes are considered the “lean” biota.i, ii

Bacteroidetes also have the ability to break down yeast that we get from food most notably found in bread, wine, and beer. This is so awesome because yeast is known to have a protective layer covering its cells that makes it nearly impossible to break down without the help of our little bacterial friends. Certain sub groups of Bacteroidetes have the skills necessary to break down the side chains and backbone structure supporting the shell around these yeast cells and keep them from proliferating in the GIT. 8 Essentially, filling your plate with more fruits and veggies can keep other bugs in check.

One of the coolest things about this class of bacteria is that it can thrive in environments within and outside of the body and tends to be found on the fiber known as hemicellulose found in plants.vii This means, the more plant sources of food we consume the greater the amount of Bacteroidetes that make it into our bodies and the better we can utilize nutrients from these types of foods. These bugs contain a strong ability to adapt to a varied diet, and rely on a mix of items on your plate. 

Now for the holiday cheer! If you are thinking, “Darn! I can’t drink any egg nog because it’s high in sugars AND fats,” or, “what about those cookies made with butter?” Relax! This is the time of the year to enjoy time with friends, family and loved ones. So, enjoy the cookies and egg nog. Just try to focus on nourishing the Bacteroidetes at the majority of your meals this season to ensure they are fully fed, equipped and ready to wage war on keeping a symbiotic balance with their nemesis: the Firmicutes. Then once the party begins, indulge a bit because remember we are ALL one happy family, and that includes the Firmicutes! We just don’t want too many of them hanging around into the New Year! 

To feed your Firmicutes make sure to load your plate with:

  • A slice of maple bourbon pecan pie
  • An extra scoop of candied yams topped with a dollop of butter (the real stuff not margarine!)
  • And what holiday dinner is complete without several slices of honey baked ham with brown butter glaze!

For bulking your Bacteroidetes take an extra helping of:

  • Oven roasted carrots with herbs
  • Brussel sprout salad with pecans and cranberries
  • And what the heck, throw some green bean casserole on your plate!


1. Walsh, C. J., Guinane, C. M., O'Toole, P. W., Cotter, P. D. (2014), Beneficial

 modulation of the gut microbiota, FEBS Letters, 588, doi:


2. Parnell, J. A., & Reimer, R. A. (2012). Prebiotic fibres dose-dependently increase satiety hormones and alter bacteroidetes and firmicutes in lean and obese JCR:LA-cp rats. The British Journal of Nutrition, 107(4), 601-13. doi:

3. Koliada, A., Syzenko, G., Moseiko, V., et. al. (2017). Association between body mass index and Firmicutes/Bacteroidetes ratio in an adult Ukrainian population. BMC Microbiology17, 120.

4. Turnbaugh, P., Ley, R., Mahowald, M. et. al. (2006). An obesity-associated gut microbiomewith increased capacity for energy harvest. Nature 4441027103. doi:10.1038/nature05414

5. Mariat, D., Firmesse, O., Levenez, F., et. al. (2009). The Firmicutes/Bacteroidetes ratio of the human microbiota changes with age. BMC Microbiology 2009 9:123.

6. Million, M., Lagier, J.C., Yahav, D., Paul, M. (2013). Gut bacterial microbiota and obesity. Clin Microbiol Infect 2013; 19: 305–313. doi: 10.1111/1469-0691.12172

7. Martens, E., Koropatkin, N., Smith, T., Gordon, J. (2009). Complex Glycan Catabolism by the Human Gut Microbiota: The Bacteroidetes Sus-like Paradigm. The Journal of Biological Chemistry 284, 24673-24677. doi: 10.1074/jbc.R109.022848

8. Cuskin, F., Lowe, E., Temple, M. (2015). Human gut Bacteroidetes can utilize yeast mannan through a selfish mechanism. Nature 2015 Jan 8; 517(7533): 165-169. doi:  10.1038/nature13995

Student Bios:

Alicia Wildman is a senior at Metropolitan State University of Denver about to complete her BSc in Human Nutrition and Dietetics. She plans to apply for a few distance internships for the Spring 2018 match and after becoming a Registered Dietitian, go on to pursue a Master’s and PhD. in biochemistry. She hopes to use her education to expand future research on the science of food. In her free time she enjoys hiking, yoga, and art as great stress relievers. 

Shawn Portwood is a senior at Metro State University of Denver pursuing his BSc in Dietetics with a minor in biology and emphasis in microbiology. His long term plans are to obtain his RD credentials as well as pursue a PhD in nutritional biology to research the microbiome. He is also a certified personal trainer (NASM CPT) and corrective exercise specialist (NASM CES). In his free time, he loves reading, training for endurance races and is obsessed with Star Wars.

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