The mouth is known to harbor many different types of bacteria, including actinomyces, bacteroides, bifidobacterium, lactobacillus, peptostreptococcus, selenomomas, treponema, veilonella1, and fungi, such as candida, cladosporum, fusarium, aspergillus, penicillium and cryptococcus.2

Modern research would suggest (but not prove, hence the lack of a reference in this case) that anomalies in the ratios of these microorganisms can wreak havoc on oral health, and potentially lead to issues like tooth decay, periodontal disease, halitosis, cavities, even cardiovascular issues.

Considering these organisms are able to survive and thrive in the mouth by feeding on the food we eat, and the immune system should theoretically be keeping these organisms from feeding on live tissue, could fasting be used as a method of resetting the playing field, so to speak, and allowing for subsequent recolonization by a healthier mix?


  1. http://cid.oxfordjournals.org/content/6/Supplement_1/S62
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3978422/figure/F2/

2 Answers 2


Oral bacteria requires tiny amounts of carbohidrates to survive. In long term fast, the glicoproteins from the saliva brings necessary carbohidrates to them to survive. But the main actor from diet, from the bacteria perspective, is the sugar, so, a sugar fast could change the composition of oral microbiota.

Now, we have the evidence that is the disbalance the ones that is associated with oral diseases and that a healthy mouth is a mouth with many different bacteria

So, the answer to your question is a partial yes: a sugar fast is the only required to change a "bad microbiome" to a "good" one. If you increase also the consumption of fruits, vegetables and some wine. The U of Rochester has some examples of good and bad food for your mouth here

TL;DR: a fast of sugar can change your oral microbiome


I didn't find any study about fasting and oral flora but in this study (PubMed Central, 2005), fasting for 8 days did not significantly change the intestinal flora in patients with fibromyalgia and rheumatoid arthritis.

Even if the mouth flora can change after fasting, it sounds logical that it would change back when you start to eat (the same foods) again.

Certain mouth bacteria, when fed by certain sugars (sucrose, trehalulose, glucose, fructose) produce acids that can cause dental caries. So, a partial fast (avoiding mentioned sugars) could theoretically decrease the risk of dental caries, but it seems that genetics and the time between sugar eating and tooth brushing are more important than the amount of sugar consumed (Nutrients Review).

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