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Tooth decay is a serious health problem around the world in both developed and developing nations and is caused by the breakdown of the tooth’s enamel. The breakdown is the result of bacteria on teeth producing acid that destroys the enamel. Bacteria’s fuel source for the production of acid are available carbohydrates from the foods and drinks that we consume throughout the day.

While the relationship between frequent consumption of free sugars and risk of tooth decay is well known, the relationship between other sources of available carbohydrate and risk of tooth decay is not.

Perhaps surprising for some, our saliva contains the enzyme amylase, which is able to break down the sugar maltose into glucose, and it is also able to breakdown some starches into glucose as well. This is particularly the case if the starchy food sticks to or is trapped between the teeth, providing adequate time for the salivary amylase to do its job. In other words, some starches may also cause tooth decay.

With this in mind, the World Health Organisation (WHO) commissioned a systematic review on starch and its effects on oral health as part of its guideline development process in 2014 and the results were published in 2019. Oral health included risk of developing dental caries (e.g., tooth decay, missing or filled teeth), periodontal disease (bleeding, periodontal, gingival indices, and periodontal pocket depth) or oral cancers (mouth, pharynx (oropharynx), throat, oesophagus and nasopharynx). The objectives were to systematically review all available published evidence pertaining to the effect on oral health outcomes of replacing rapidly digestible starch (RDS) with slowly digestible starch (SDS) in the diet, and also the impact of total starch intake on oral health.

After searching 6 electronic databases, 33 papers (28 studies) were included for the RDS versus SDS comparison, and for total starch, 23 papers (22 studies) were included. Overall, there were few studies in each particular disease category, and most were observational in nature. Therefore, there was limited evidence overall to answer the specific questions, and the evidence that does exist was judged to be of low quality.

Tooth decay

  • There was a positive association between RDS consumption and risk of developing dental caries. In other words, the more RDS consumed, the higher the number of dental caries.
  • There was no association with total starch consumption and tooth decay.
  • However, total starch increased risk of dental caries when it was combined with sugars. In other words, when biscuits, cakes, cookies, sweet pastries, etc…were consumed.

Periodontal disease

  • Only one study investigated the effect of RDS vs. SDS on the risk of periodontitis, and it found that consumption of SDS (in the form of wholegrains) reduced the risk.


  • There was a positive association between consumption of RDS and risk of oral cancer.
  • Only one included study investigated the association between total starch consumption and oral cancer, and it found no association.

The overall conclusions were that RDS intake, but not total starch intake, is associated with increased risk of dental caries. There is limited evidence suggesting that whole grains (i.e., SDS) may protect against oral cancers. In line with advice for general health, dental health professionals should promote consumption of SDS, and advocate limiting RDS, especially when combined with free sugars. While it may sound like a cliché, given the importance of dental health, more high-quality research is definitely needed into this important issue.

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Dr Alan Barclay, PhD, is a consultant dietitian and chef with a particular interest in carbohydrates and diabetes. He is author of Reversing Diabetes (Murdoch Books), and co-author of 30-plus scientific publications, The Good Carbs Cookbook (Murdoch Books), Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment Publishing).

Contact: Follow him on Twitter, LinkedIn or check out his website.