Oral Microbiota – Meat-Eaters & Plant-Eaters

We’ve already looked at gut1  and urinary2 microbiota, and what fun we had! But what about the miniature world of bacteria in the mouth – the microbiota in our saliva? Saliva might not seem that important, but in the long and complex digestive saga, it’s Chapter One Page One.

There’s hardly any current research into the possible variance between the salivary microbiota of plant-eaters and meat-eaters, but a 2018 study3 wanted to find out differences between vegan and omnivore diets in relation to salivary microbiota. Was there any difference between it and the saliva of our meat-eating friends? Answers on a postcard to… Well, there were some differences, as one might possibly expect.

One apparent variance seemed to be the result of the amount of fibre in vegans’ diets. The researchers state that: “Our results indicate that the intake of total dietary fibre is associated with increased abundance of the oral commensals Capnocytophaga and Neisseria subflava, as well as an increase in the potential for short-chain fatty acid (butyrate and propionate) production.”   This follows earlier studies4 5 suggesting that there’s an inverse relationship between the effects of higher consumption of dietary fibre on oral microbiota and lower risk of both prevalent and incident periodontal disease. (Incident cases are those that are newly diagnosed diseases of interest. Prevalent cases are those whose disease developed or was diagnosed before they were identified for the study.) The latter beneficial effect of fibre seems to be especially related to cereal fibre.

An intriguing finding of this study was that one of the bacteria found more in vegans than omnivores (viz. Campylobacter rectus) was positively associated with CRP (C-reactive protein  – a marker for inflammation) which is a species associated with periodontal disease. There were no definitive conclusions drawn as to whether this meant that we could expect more vegan teeth to drop out that omnivores’. That would be quite surprising, considering the wealth of evidence6 that supports the anti-inflammatory power of a plant-based diet compared with a meat-heavy diet.  There is no indication in the study whether members of the vegan group selected are eating a whole food plant-based diet without added salt, oil and sugar (non-SOS WFPBD). My guess (and it’s only that) is that they are not.

However, the implication of this might be that the vegan diet covered in this study is far from the sort of food consumed in a non-SOS WFPBD. It’s certainly the case that every vegan restaurant I have visited seems to compensate for the lack of yummy meaty/milky/cheesy tastes with lots more sugar, oil and salt than I would ever recommend. Did the vegans included in this study compensate for the the lack of cheesy morsels by eating more sweeties rather than fruits, nuts and seeds? Whilst the researchers do not, of course, address this issue, they do say: “Participants in the present study were not subjected to a dental examination. Consequently, we cannot know whether the enrichment of C. rectus in vegan saliva reflects poor periodontal health.” There is also insufficient evidence that the presence of C. rectus actually means that periodontal disease exists. The researchers referred to an earlier study7 in this context: “C. rectus was more abundant in saliva from individuals with gingivitis or periodontitis, but receiver operator characteristic analysis showed that the presence of periodontal disease could not be reliably identified by the salivary abundance of C. rectus.”

What would be useful is a thorough study of the difference between a non-SOS WFPBD and other diets in order to see whether just eating unprocessed whole plant foods would really cause any problems with our gums or teeth.

The researchers continue to state that: “Dietary patterns have been shown to have a substantial impact on the functional potential of the gut microbiota… Our results indicate that similar effects may apply to the salivary microbiota. Of notice, vegans eat significantly less protein compared to omnivores and the proportion of imputed genomic content encoding peptidase enzymes was also lower in vegans. Conversely, pathways involved in the metabolism of some of the amino acids least abundant in the vegan diet were enriched in vegans, perhaps reflecting a competitive edge for bacteria better equipped at utilizing amino acids in a habitat where this particular substrate is scarce. Similarly, the imputed potential for lipid and fatty acid biosynthesis was increased in the vegan microbiome. Increased in vegans were also the pentose phosphate pathway, pyruvate metabolism, and the potential for biosynthesis of the short-chain fatty acids butyrate and propionate. This pattern of enriched carbohydrate metabolism might reflect the higher intake of dietary fibre. 

They concluded: “…our study of the salivary microbiome in vegans and omnivores suggest that long-term dietary patterns and specific nutrients contribute in shaping the salivary microbiota. Our finding that certain oral bacteria are associated with circulating inflammatory markers provide further evidence to the proposed link between the oral microbiota and systemic disease.

Many question remain about this specific area of salivary microbiota and how it relates to/affects our overall health. There were, to the best of my knowledge, no saliva samples taken from individuals to analyse salivary microbiota in the individuals in wide-reaching population studies such as the China Study8 or the Nurses’s Health Study9 . However. my guess (and it’s just that that – until it’s put to the test) is that the oral health of those who eat a non-SOS WFPBD will be the healthiest human saliva.

We’ll just have to wait until the researchers spit out the results…


  1. Two Types of Gut Bacteria: Plant Eaters’ & Meat Eaters’ []
  2. Urinary Microbiome & Psychological Issues in Women with Overactive Bladder []
  3. Sci Rep. 2018; 8: 5847. Impact of a vegan diet on the human salivary microbiota. Tue H. Hansen, corresponding author Timo Kern, Emilie G. Bak, Alireza Kashani, Kristine H. Allin, Trine Nielsen, Torben Hansen, and Oluf Pedersen. []
  4. Dietary Fiber Intake Is Inversely Associated with Periodontal Disease among US Adults. Nielsen SJ, Trak-Fellermeier MA, Joshipura K, Dye BA. J Nutr. 2016 Dec; 146(12):2530-2536. []
  5. Whole-grain and fiber intakes and periodontitis risk in men. Merchant AT, Pitiphat W, Franz M, Joshipura KJ. Am J Clin Nutr. 2006 Jun; 83(6):1395-400. []
  6. How Does Meat Cause Inflammation? Written By Michael Greger M.D. FACLM on September 20th, 2012 []
  7. Salivary infectious agents and periodontal disease status. Saygun I, Nizam N, Keskiner I, Bal V, Kubar A, Açıkel C, Serdar M, Slots J. J Periodontal Res. 2011 Apr; 46(2):235-9. []
  8. The China Study []
  9. Nurse’s Health Study []