Crunch Time for Digestion: Teeth and Saliva Matter

Although digestion begins with the cephalic phase, a lot goes on in the mouth at mealtime:

• Chemical digestion 
• Mechanical digestion
• Immune interactions with microbial and food antigens 
• Oral microbiota interactions with host cells and food 
• Sublingual B12 absorption 
• Taste perception
• Swallow preparation..and more! 

Two key players for digestive health in the mouth are saliva and teeth. 

Saliva is designed for its important multifunctional role: protection, pH balance, lubrication, and chemical digestion. 

It is mostly water with protein, especially lubricating mucin glycoproteins and both digestive and antimicrobial enzymes.[1] Saliva has defensive immunoglobulins like secretory IgA that keep too many microbes from getting too close, and a small amount of buffering salts, minerals, and carbohydrates.[1] While we chew, the water and enzymes in saliva dissolve food components so that they can reach and stimulate taste receptors on the tongue.[1]

Outside of meals, saliva works round-the-clock protecting us by trapping and removing food debris and microbes from the mouth, while adding a constant protective layer.[1] As if all that was not enough, saliva contains certain hormones, and might promote wound healing.[1] 

So don’t ignore a dry mouth! 

Dry mouth can be a pharmaceutical side effect, or it can signal dehydration or other serious health conditions such as Sjrogren’s syndrome. If slowing down to promote the cephalic phase response is not enough, there is no need to leave your body lacking. Doctors and dietitians can recommend lubricating tablets and mouthwashes--or even tart foods--to help. A dry mouth can also hurt your teeth and gums since saliva helps to protect them.

Teeth are responsible for mechanical digestion--the mashing and slicing of food so it can be better mixed with saliva. When we cannot or do not chew well, not only is there less interaction with taste receptors and a greater risk of problems swallowing, but we are kicking more digestive responsibility to the rest of the GI tract while giving it less time to prepare.[2-4] Insufficient chewing means less mixing with saliva and less gastric secretion.[4]

In fact, IBS and various digestive disturbances appear associated with tooth loss and chewing insufficiency.[3-4] Factors such as the cause for missing teeth, like periodontitis, or the consequences of missing teeth, such as diet changes, can both play roles in IBS and more research is needed.[3-4] Thankfully, there is a lot we can do with oral hygiene and dental care to keep healthy teeth and gums. 

So…should we “chew 30 times per bite” (or any other number) as a rule? 

This would be an extremely practical guideline and should not be harmful, but it is not generalizable. The number of necessary chews depends on the food and the individual: blended butternut squash soup and steak are not the same, and individuals with GI surgeries like bariatric procedures can require more thoroughly chewed food. Naturally over the course of a meal, the rate and weight of mouthfuls tends to decrease [5] and this could also affect the number of chews necessary. Time matters, too, for interaction with taste receptors and saliva, and likely for satisfaction. Chewing bites for 30 seconds decreased snack consumption in one study.[6]

So without a generalizable guideline, to benefit from more chewing, get curious about your habits, dental health, and digestion. Set reasonable goals to promote cephalic phase responses and chewing, such as extending a meal by 5 minutes or chewing 10 more times per bite from your baseline. And take at least three daily actions that would make your dentist smile.  

1. _{Kumar B, Kashyap N, Avinash A, et al. The composition, function and role of saliva in maintaining oral health: A review. Int J Contemp Dent Med Rev. 2017;2017: 1-6. doi: 10.15713/ins.ijcdmr.12.}
2. _{Furuta M, Yamashita Y. Oral Health and Swallowing Problems. Curr Phys Med Rehabil Rep. 2013;1(4):216-222. Published 2013 Sep 15. doi:10.1007/s40141-013-0026-x}
3. _{Esmaillzadeh A, Keshteli AH, Saneei T, Saneei P, Savabi O, Adibi P. Is tooth loss associated with irritable bowel syndrome?. J Oral Rehabil. 2015;42(7):503-511. doi:10.1111/joor.12277}
4. _{Khayyatzadeh SS, Kazemi-Bajestani SMR, Mirmousavi SJ, et al. Dietary behaviors in relation to prevalence of irritable bowel syndrome in adolescent girls. J Gastroenterol Hepatol. 2018;33(2):404-410. doi:10.1111/jgh.13908}
5. _{Ioakimidis I, Zandian M, Eriksson-Marklund L, Bergh C, Grigoriadis A, Södersten P. Description of chewing and food intake over the course of a meal. Physiol Behav. 2011;104(5):761-769. doi:10.1016/j.physbeh.2011.07.021}
6. _{Higgs S, Jones A. Prolonged chewing at lunch decreases later snack intake [published correction appears in Appetite. 2017 Sep 1;116:616. Appetite. 2013;62:91-95. doi:10.1016/j.appet.2012.11.019}