Yes, the ketogenic diet can cause a noticeable change in body odor, often called “keto odor” or “keto breath.” This temporary side effect occurs when the body transitions into ketosis, the metabolic state achieved by following the high-fat, very low-carbohydrate eating plan. By restricting carbohydrates, the body is forced to find an alternative fuel source and begins burning fat for energy. The odor is generally strongest during the initial adaptation phase and subsides as the body becomes more efficient at utilizing this new fuel source.
The Metabolic Cause of Keto Odor
The unique odor stems from the body’s shift from using glucose to burning stored fat. When carbohydrates are restricted, the liver breaks down fatty acids, converting them into ketone bodies: acetoacetate, beta-hydroxybutyrate, and acetone. Acetone is the simplest ketone body and the primary volatile compound responsible for the distinctive odor. Unlike the other two ketones, acetone is a waste product that cannot be metabolized and must be excreted. The buildup of this compound leads to its expulsion through various routes. The characteristic scent is often described as fruity, sweet, or similar to nail polish remover. This metabolic process is a sign of nutritional ketosis, which is distinct from diabetic ketoacidosis.
Where the Odor Comes From
The odor manifests in three primary locations as the body works to eliminate excess acetone.
Keto Breath
The most recognized form is “keto breath,” which occurs when volatile acetone is expelled through the lungs during respiration. This results in a persistent, noticeable scent separate from typical bad breath caused by oral hygiene issues.
Keto Sweat
Acetone is also excreted through the skin’s sweat glands, contributing to a generalized body odor known as “keto sweat.” As this compound is released through perspiration, it changes the scent profile of the sweat itself, which is particularly noticeable during exercise or in warm conditions.
Urine Excretion
Finally, excess ketone bodies, including acetoacetate and beta-hydroxybutyrate, are flushed out through the kidneys and excreted in the urine. The presence of these compounds can give the urine a stronger, more pungent smell.
Practical Strategies for Reducing the Smell
While the odor is temporary, several practical steps can help mitigate the smell while the body adjusts.
Increase Hydration
Increasing water intake is an effective strategy, as adequate hydration helps dilute the concentration of ketones and encourages their faster excretion through the urine. Drinking plenty of water helps the kidneys flush out the excess byproducts more efficiently.
Improve Oral Hygiene
Improving oral hygiene can directly address the breath odor, even though the cause is metabolic, not bacterial. Brushing, flossing regularly, and using mouthwash can help mask the acetone being expelled from the lungs. Chewing sugar-free gum or mints can also provide a temporary solution by stimulating saliva production.
Adjust Macronutrients
Slightly adjusting the macronutrient balance may offer relief. Marginally increasing carbohydrate intake, perhaps by five to ten grams, can slow the rate of ketone production, easing the adaptation phase. Moderating protein consumption is also helpful, as high protein intake can lead to the production of ammonia, which contributes to a strong body odor.
The odor is most pronounced in the first few weeks. As the body becomes “keto-adapted,” tissues utilize acetoacetate and beta-hydroxybutyrate more efficiently. This increased utilization reduces the amount of excess acetone that needs to be expelled, causing the noticeable odor to diminish or disappear completely.