Eating a low-carbohydrate diet (such as the Atkins diet, ketogenic diet, South Beach diet) may cause some side effects. Although not everyone may suffer from keto breath, it is one of the most common symptoms.
Some people describe bad breath as a rotten fruit or metallic taste, while others describe it as the smell of nail polish.
The good news is that this unpleasant smell is actually a good sign. It indicates that your body has entered a state of ketosis, which means that you are starting to burn fat.
What Are The Causes Of Keto Breath?
There are many causes of bad breath, such as oral bacteria, periodontitis and gastrointestinal problems.
However, if you have bad breath after following a low-carb diet, there are basically two reasons:
- Your body produces a lot of nutritional ketone bodies which are products of metabolizing fat.
- Your body produces a large amount of ammonia which is a product of metabolizing protein.
1. Ketosis
One of the main energy sources of your body is glucose. When you eat carbohydrates, they are broken down from complex sugars into simple glucose molecules during digestion.
If you drastically reduce your carbohydrate intake, your body will look for alternative energy sources (in this case, fat) to obtain energy. This metabolic state is called ketosis.
When your body breaks down fatty acids, it produces a by-product called ketones [*]. Common ketone bodies appear in three forms:
- acetoacetate
- beta-hydroxybutyrate
- acetone
These ketone bodies are regularly eliminated from your body through urination and breathing.
As your body consumes more fat, more ketones are released. Therefore, excessive accumulation of ketones in your body may cause bad breath.
2. Protein metabolism
Any major changes in your diet will more or less affect the way your body metabolizes food. The ketogenic diet is a good example.
We know that when protein is broken down in the body, it produces ammonia.
The ketogenic diet requires a strict restriction of the intake of carbohydrates while increasing protein and fat intake.
This sudden increase in protein will inevitably increase the amount of ammonia in both your stomach gases and urine. [*]
In addition, your body needs a lot of water to excrete ammonia. Therefore, a lack of water in the body can cause ammonia to accumulate rapidly. As a result, you may experience bad breath.

What Does Keto Breath Smell Like?
Generally speaking, bad breath is very common. It is usually caused by bacteria in the mouth.
When oral bacteria start to decompose the food you eat, they produce volatile sulfur compounds (VSC). These compounds have a sulfur smell (smells like rotten eggs). [*]
However, keto breath is different. The smell may vary depending on the by-products of protein or fat metabolism.
For example,
- Acetoacetate and β-hydroxybutyrate may make your breath smell fruity, which some people describe as similar to rotten apples.
- Acetone produces a more resinous smell when breathing (like nail polish).
- Excessive protein metabolism can cause ammonia gas in your breath and urine.
How To Get Rid Of Keto Breath?
In most cases, bad breath caused by eating a ketogenic diet will disappear on its own. However, it may last for several weeks.
This kind of breath can certainly make you feel uncomfortable and even affect your social interaction.
You can use some simple methods to dilute and cover up your keto breath.
1. Drink plenty of water
Try to drink at least 8 glasses of water a day.
This not only helps to remove excess ketones and ammonia from your body but also helps your digestion and prevents constipation.
2. Reduce protein intake and eat more fat
This may require repeated experimentation.
First, eat enough protein according to the standard ratio of the keto diet.
Then gradually reduce your protein. In addition, you can increase the intake of healthy fats (such as avocado and macadamia nuts), and then you can increase your protein intake again.
This simple conversion and circulation from high protein to high fat can reduce excessive ammonia and acetone emissions. After a while, you should notice a fresher breath.
3. Maintain good oral hygiene
Brush your teeth often and develop the habit of using dental floss and antibacterial mouthwash. Regular tongue scraping can also help.
4. Try natural breath fresheners:
Some natural breath fresheners, such as mint, parsley, cloves, cinnamon and anise can help you reduce the bad breath.
If you can tolerate the taste, you can chew them.
5. Sugar-free gum
Gum is always a good choice when you have bad breath.
However, you must be cautious to choose “sugar-free” gum if you follow a keto diet.
6. Slightly increase your carb intake
If you currently eat 20 grams of net carbs per day, you can try to increase it to 25 grams to see if there are any changes.
This should reduce the amount of excess ketone bodies, thereby reducing bad breath.
Summary:
Keto breath is one of the common side effects during the early stage of a low-carb diet. In addition to bad breath, most people also experience other symptoms of keto flu.
Although this discomfort will only last for a while, the good news is that once these symptoms appear, it means that your body has entered a state of ketosis, that is, you are starting burning fat.
Also, these side effects are temporary. As long as you stick to a healthy low-carb diet, these symptoms will slowly disappear.
Your body needs time to adapt to any major changes in diet. A healthy diet can not only help you lose weight, it can also improve your overall health.