Why Low-Carb Diets Cause Keto Breath

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Bad breath is one of the possible side effects of a low-carb diet, such as the Atkins Diet, South Beach Diet or Dukan Diet. Known as ketosis breath, or simply keto breath, the condition is often accompanied by a foul taste in the mouth. Symptoms like these can be distressing, but there are things you can do to overcome them without undermining the goals of your diet.


There are many causes of bad breath. However, with low-carb diets, there are two primary culprits: ketosis (the metabolic state achieved with a low-carb diet) and protein metabolism.


One of the body's primary sources of energy is glucose. Glucose is created when the digestive tract breaks down carbohydrates from complex sugars to simple glucose molecules.

When you reduce the number of carbs you eat, your body has to find alternative fuel sources (namely fat) for energy—a metabolic state known as ketosis.

When the body breaks down fatty acids, it creates a byproduct known as ketones. Common ketone bodies come in three forms: acetoacetate, beta-hydroxybutyrate, and acetone. These ketone bodies are regularly removed from your body through urination and exhalation.

If you're on a low-carb diet, your body is relying more on fatty acids for energy because you aren't eating as many carbohydrates. As your body uses up more fat, more ketones will be released as a byproduct of the metabolic process at work.

The excessive accumulation of ketones in your body can contribute to bad breath. However, the ketones you exhale have very distinctive scents—most of which are unlike what you would experience with everyday bad breath (halitosis).

Protein Metabolism

Changes in your diet can also trigger changes in your breath. With a low-carb diet, the sudden switch from carbs to proteins alters how your body metabolizes food. The breakdown of protein in the body creates ammonia. A sudden surge in dietary protein will only amplify this effect, increasing the amount of ammonia in both your stomach gases and urine.

Because it takes a lot of water to excrete ammonia, inadequate hydration can lead to a worsening of your bad breath as ammonia rapidly accumulates in the body.


Keto breath varies from person to person but is generally not the same as halitosis. The bad breath most of us experience from time to time is caused by bacteria in our mouths.

When these bacteria start to break down the food we eat, they create volatile sulfur compounds (VSCs). Usually, these compounds have a sulfurous odor (similar to rotten eggs).

With keto breath, characteristics of the smell vary based on which byproducts of protein and fat metabolism are produced. For example:

  • Acetoacetate and beta-hydroxybutyrate can cause your breath to smell sweet and fruity. Some people describe the odor as similar to bruised or rotting apples.
  • Acetone on the breath creates more of a resiny smell (like nail polish).
  • Excess protein metabolism can cause both your breath and urine to have an aroma of ammonia.


In most cases, keto breath disappears on its own—though it may take several weeks to a month. If you've committed to a low-carb diet, here are a few ways to mitigate the symptoms of keto breath while your metabolism adjusts.

  • Drink more water. Aim for no less than eight 8-ounce glasses of water per day. This not only helps flush excess ketones and VSC from your body, but it also aids in digestion and prevents constipation.
  • Change the balance of proteins you consume. While this is a trial-and-error process, a change of protein sources—say, from chicken to meat or meat to fish—can sometimes alter which ketone bodies are being produced (mainly by the types of fatty acids begin broken down).
  • Increase fat intake. Research suggests that increasing fat while reducing protein consumption can help minimize both acetone and ammonia emissions.
  • Don't undercut the carbs. Don't be overzealous and cut out more carbs than you need. The South Beach Diet, for example, is not as strict on the carb count as the Atkins Diet. Neither, however, aims for a zero-carbs policy. If you suspect you've gone overboard on carb cutting, try increasing your intake of healthy carbs within the prescribed limit.
  • Practice good oral hygiene. Brush your teeth, floss, and rinse with an antibacterial mouthwash. Regular tongue scraping can also help.
  • Mask your breath. Try natural breath fresheners (such as mint, parsley, cloves, cinnamon, or fennel seeds) or breath capsules made from parsley oil or chlorophyll.

Sugar-free mints and gums made with xylitol can help mask bad breath while exerting mild antibacterial properties to control VSC.

A Word From Verywell

If your bad breath persists for more than a couple of months despite good oral hygiene practices and your best efforts to staunch it, speak with your doctor or dentist. In some cases, bad breath may have nothing to do with your low-carb diet. It could be related to dry mouth, gum disease, or medical conditions such as acid reflux, diabetes, sinus problems, or liver or kidney disease.

5 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Dhillon KK, Gupta S. Biochemistry, Ketogenesis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-.

  3. Levitt DG, Levitt MD. A model of blood-ammonia homeostasis based on a quantitative analysis of nitrogen metabolism in the multiple organs involved in the production, catabolism, and excretion of ammonia in humans. Clin Exp Gastroenterol. 2018;11:193-215. https://doi.org/10.2147/CEG.S160921

  4. Kapoor U, Sharma G, Juneja M, Nagpal A. Halitosis: Current concepts on etiology, diagnosis and management. Eur J Dent. 2016;10(2):292-300. https://doi.org/10.4103/1305-7456.178294

  5. Prabhakar A. Quach A. Zhang H et al. Acetone as biomarker for ketosis buildup capability - a study in healthy individuals under combined high fat and starvation diets. Nutr J. 2015;14:41. doi:10.1186/s12937-015-0028-x

Additional Reading

By Laura Dolson
Laura Dolson is a health and food writer who develops low-carb and gluten-free recipes for home cooks.