Can You Brush Your Teeth While Fasting?

Brushing teeth while fasting will not break the fast. Combined with intermittent fasting, brushing will improve oral health and hygiene.
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If you’re wondering, Can I brush my teeth while fasting? The answer is yes. There may be a small chance of breaking the fast due to the sweetness of the toothpaste flavor on the tongue (triggering insulin release) or if the toothpaste is swallowed. But the benefits of brushing your teeth while intermittent fasting outweigh this minute risk.

Written by
Jill Lebofsky
15+yr Women's Wellness Expert, Holistic Menopause Support, Intermittent Fasting, Midlife, Essential Oil, Author, Speaker

Since childhood, dentists have impressed upon us the importance of teeth brushing. We were told that we should – at the very least – brush our teeth when we wake up and before bed.

Plus … morning breath … yuk!

If you’re beginning the intermittent fasting journey, you’ve been told not to eat or drink anything (or consume minimal items) during the fasting period, so you don’t break your fast and discontinue fat burning.

But many wonder whether brushing teeth while fasting breaks the fast.


What breaks a fast?

There are different thoughts on what foods and drinks may break a fast when intermittent fasting. If your goal with intermittent fasting is to burn fat then learning to stay in a fasted state for a set amount of time is vital for success.

Regardless of the method of intermittent fasting, the body gets into fat-burning mode when blood sugar and insulin levels are significantly lowered and stay there for a period. At this point, the body has used up the fuel from the last meal and turns to stored fat for energy. Carbohydrates spike insulin levels. However, research shows that consuming fewer than 50 grams of carbohydrates a day won’t raise blood sugar levels enough to trigger insulin release (1). Increased insulin levels are what break the fast.

There are two schools of thought on calorie consumption while fasting. Technically, any number of calories breaks a fast. Some people adhere to a “clean” fast, drinking only water or possibly adding in black coffee or unsweetened tea. Others follow a “dirty fast” and allow a few high-fat items such as coconut oil or butter or allow a tiny amount of lemon or lime juice.

Some people say it is OK to chew sugarless gum or use an artificial sweetener during a fast if it contains zero calories. The issue with this is that the mere taste of sweetness on the tongue receptors may enhance insulin release, regardless of calories (2). This is where the question of can you brush your teeth while fasting arises.


Does toothpaste contain carbohydrates or sugar that would break the fast?

blue-white toothpaste on a blue toothbrush.

Toothpaste doesn’t contain sugar, but many commercial toothpastes are sweetened with artificial sweeteners, so technically, brushing your teeth could break your fast. Realistically, unless you swallow the toothpaste, the small amount used will most likely not raise blood sugar and insulin levels and will not break the fast.

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Should you be brushing teeth while fasting?

You need to weigh the pros and cons and decide for yourself about brushing teeth while fasting.


Intermittent fasting by itself naturally improves oral health (3). Combining intermittent fasting with regular teeth brushing will not only help you lose weight, but can also improve tooth decay and gum disease.

When intermittent fasting, dry mouth may occur. Dry mouth encourages harmful acids, plaque, and food remnants to stay on the teeth, often resulting in tooth decay, enamel erosion, and gingivitis (gum disease). Dry mouth may lead to bad breath. Brushing your teeth removes the odor-causing bacteria and freshens your breath so you can converse with others confidently.

Some intermittent fasters report a metallic taste in their mouth while fasting. This is due to the byproduct acetone being released into the blood and breath during the fat-burning process (4). Brushing teeth while fasting will ultimately reduce the bad taste in the mouth. 


The slim possibility of breaking your fast.


Natural toothpastes

White toothpaste on a turquoise toothbrush.

Although toothpaste doesn’t have added sugar, the artificial sweeteners used for flavor may impact your general health and weight-loss efforts (5). Seek out natural toothpaste substitutes for the well-known commercial brands. Find ones that are free of dyes, artificial sweeteners, and artificial flavors. Consider making your own or using alternative toothpaste containing baking soda, coconut oil, herbs, essential oils, and other natural healthy teeth or fresh breath promoting items.


The bottom line

For the sake of everyone around you and for your own dental health benefits, continue brushing your teeth at least twice a day when intermittent fasting. Have no fears about breaking your fast while brushing your teeth. Unless you swallow toothpaste, the chances of it spiking your insulin and breaking your fast are slim. Intermittent fasting and teeth brushing are important for improving and maintaining your oral health and hygiene.

Check out these intermittent fasting mistakes you should avoid.

Get the answers to other important questions for success with intermittent fasting by joining this online group of intermittent fasting women.


  1. Masood W, Annamaraju P, Uppaluri KR. Ketogenic Diet. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan.
  2. Takai S, Yasumatsu K, Inoue M, et al. Glucagon-like peptide-1 is specifically involved in sweet taste transmission. FASEB J. 2015;29(6):2268-2280. doi:10.1096/fj.14-265355
  3. Branch-Mays GL, Dawson DR, Gunsolley JC, et al. The effects of a calorie-reduced diet on periodontal inflammation and disease in a non-human primate model. J Periodontol. 2008;79(7):1184-1191. doi:10.1902/jop.2008.070629
  4. Anderson JC. Measuring breath acetone for monitoring fat loss: Review. Obesity (Silver Spring). 2015;23(12):2327-2334. doi:10.1002/oby.21242
  5. Shepard P, Nudi L, Tozzo E, Yang H, Leach F, Kahn B. Adipose cell hyperplasia and enhanced glucose disposal in transgenic mice overexpressing GLUT4 selectively in adipose tissue. Journal of Biological Chemistry. 1993;268(30):22243-22246. doi:10.1016/S0021-9258(18)41516-5

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