13 Ketosis Symptoms: How to Know When It Is Working

Physical changes are normal when getting into ketosis as the body adapts to the new source of energy. Dry mouth, keto flu, fatigue, muscle cramps, sleep changes, exercise performance and digestion changes, weight loss, and a more stable energy source are often noticeable ketosis symptoms.

This article will help you understand why these changes occur and provide tips on dealing with them.

1. Increased Ketone Levels

Although not technically a symptom, an increased blood ketone level is the most accurate way to know that you have entered ketosis. Moreover, breath breath and urine acetone1 also indicate ketosis.

Ketones, specifically beta-hydroxybutyrate (BHB), acetoacetate, and acetone, are byproducts of fat metabolism. As your body shifts from utilizing glucose to breaking down fats for energy, these ketones become increasingly prevalent in the bloodstream.

Typically, ketone levels ranging from 0.5 to 3.0 mmol/L indicate nutritional ketosis.2 This range ensures your body efficiently uses fats for energy without entering potentially harmful levels of ketosis.

2. Dry Mouth and Keto Breath

Two common side effects associated with ketosis are dry mouth and what is commonly referred to as keto breath, which people describe as similar to nail polish.

Ketosis is a natural diuretic, which means increased kidney water excretion.3 This can contribute to a sensation of dryness in the mouth.

Moreover, acetone, a type of ketone, is a natural byproduct of fat metabolism in ketosis. It can be released through breath,4 which could also be used to measure one’s state of ketosis.

Maintaining meticulous oral hygiene, including regular brushing, flossing, and hydration, can help manage the keto breath. Chewing sugar-free gum or mint leaves may also provide temporary relief.

3. Keto Flu

headache is among the ketosis symptoms

Keto flu is one of the most commonly experienced symptoms of ketosis. As the name implies, keto flu consists of flu-like symptoms,5 which may be due to the following:

  • Carbohydrate Withdrawal: The keto flu arises primarily due to the withdrawal of carbohydrates, leading to a temporary shortage of glucose—the body’s primary energy source.
  • Electrolyte Imbalance: During the initial stages of ketosis, the body excretes excess water and essential electrolytes. This can result in imbalances, contributing to fatigue, headaches, and muscle cramps.

The duration and intensity of keto flu symptoms vary among individuals. While some may experience it for a few days, others may navigate this phase relatively unscathed. Hydration and electrolyte supplementation help manage keto flu.

4. Fatigue

In the early stages of ketosis, the body adjusts to utilizing fats and ketones for energy instead of glucose. This transition can temporarily result in feelings of fatigue and lethargy.6

As the body depletes its glycogen stores (the storage form of glucose), energy levels may initially dip before stabilizing with the increased utilization of fats.

Ensuring adequate hydration is crucial during ketosis. Dehydration can exacerbate feelings of fatigue, so consistent water intake is essential. Electrolyte supplements could also help manage fatigue.

5. Muscle Cramps

Ketosis can increase electrolytes’ excretion, particularly sodium, potassium, and magnesium. Insufficient levels of these minerals may contribute to muscle cramps.7

Hydration, engaging in moderate exercise, and incorporating foods rich in electrolytes, such as leafy greens, low-carb nuts, and seeds, can help maintain balance. Consider supplements if necessary, especially during the initial stages of ketosis.

6. Sleep Changes

Entering ketosis can influence sleep patterns, with some individuals experiencing improvements while others may initially face disruptions. This is mainly due to the body adapting to the low-carb diet.

Ketosis can impact the production of neurotransmitters such as serotonin8 and melatonin,9 influencing sleep-wake cycles. However, individual responses may vary, and long-term following of the keto diet shows promise in improving sleep patterns.10

Maintaining a regular sleep schedule promotes circadian rhythm alignment. Pay attention to your sleep patterns and make adjustments as needed. If disruptions persist, consider consulting with a healthcare professional.

7. Temporary Decrease in Exercise Performance

Your energy production mechanisms may not be optimized for high-intensity workouts as the body transitions from relying on glycogen stores to efficiently utilizing fat and ketones.

This happens due to decreased glycogen, a primary fuel source for intense, anaerobic exercise.11

However, note that this decrease is often temporary. As your body becomes more adept at utilizing ketones and sparing glycogen, exercise performance tends to stabilize and, in some cases, improve.12

8. Changes in Digestion

You may experience changes in digestion due to the reduction in carbohydrate intake, often accompanied by a decrease in fiber from grains and certain fruits, which can influence the composition and diversity of gut microbiota,13 causing either constipation or diarrhea.

Incorporate fiber-rich, low-carb vegetables, nuts, and seeds to maintain gut health. Consider incorporating probiotics and fermented foods to support a healthy gut microbiome.

Lastly, ensure proper hydration and electrolyte balance.

9. Reduced Cravings

While some may experience increased hunger on the first days of getting into ketosis, this decreases immensely as you continue the diet.14 The low-carbohydrate intake helps regulate insulin and ghrelin, a hormone involved in hunger and satiety.15

Ketosis tends to increase the production of satiety hormones, such as leptin.16 This hormonal balance contributes to a feeling of fullness, reducing the desire for frequent snacking.

Focus on whole, nutrient-dense foods rich in fats, proteins, and fibrous vegetables. These choices contribute to sustained energy levels and satiety.

10. More Stable Energy

As your body adjusts, you will notice a more stable energy. The liver produces ketones, a highly efficient and consistent energy source, especially for the brain and muscles.17

The body experiences reduced fatigue throughout the day with a continuous fuel source. Individuals often report sustained energy levels without frequent snacks or meals.14

11. Improved Focus

During the maintenance phase of ketosis, you will likely notice an increase in mental clarity, focus, and concentration.18 Steady energy levels are particularly beneficial for the brain, which thrives on a consistent energy supply.

Subjects also do not experience brain fog, which most people suffer from after taking a high-carbohydrate meal. Some subjects also manifest better sleep patterns, especially among children with therapy-resistant epilepsy.19

12. Weight Loss

Weight loss is one of the most sought-after effects of ketosis, which becomes visible as early as 2 weeks after following the keto diet. Research suggests the keto diet is far more effective than a low-fat diet.20

Studies suggest that weight loss is mainly due to a low carbohydrate intake. A low-carb diet lowers blood sugar and insulin levels, which warrants fat burning.

It’s vital to note that the weight loss following ketosis varies among individuals, and a calorie-deficit diet21 and regular exercise help you get a more sustainable weight loss.

13. Sustained Fat Loss

Beyond initial weight loss, ketosis supports sustained fat loss, emphasizing the long-term benefits of the ketogenic lifestyle. Moreover, the keto diet also preserves muscle mass,22 which is crucial in maintaining a healthy physique.

With prolonged adherence to ketosis, the body becomes more efficient at oxidizing fat for energy.23 This metabolic flexibility enhances the ability to utilize fat stores, facilitating sustained fat loss.

Among obese subjects, the keto diet has been shown to reduce BMI, and waist circumference and improve cholesterol and triglyceride levels.24


Experiencing temporary symptoms during ketosis is common and should mean that your body is undergoing adjustments and necessary changes. Patience is vital with all the ketosis symptoms, hydration, and a well-balanced meal.

While common, you should seek professional help if you experience these symptoms for prolonged periods.

Frequently Asked Questions (FAQ)

Is it good for your body to be in ketosis?

Yes, for many individuals, entering and maintaining a state of ketosis can have numerous health benefits. From improved metabolic markers to enhanced mental clarity, ketosis is considered a safe and effective nutritional strategy when implemented appropriately.

How long is it safe to be in ketosis?

Experts suggest that it’s safe to stay in ketosis for up to 12 months, but the safety and duration of ketosis can vary from person to person. While short-term ketosis is generally safe for most individuals, long-term adherence to a ketogenic diet should be done under medical supervision, especially for those with underlying health conditions.

What are the stages of ketosis?

The stages of ketosis typically include the initiation phase, where the body adapts to low-carbohydrate intake, followed by the adaptation phase, where it becomes efficient at utilizing ketones for energy. Lastly, the maintenance stage is where the body continuously uses ketones for energy following a low-carbohydrate intake.

Is it healthy to be in ketosis all the time?

While short-term and intermittent ketosis can have health benefits, the long-term sustainability of a continuous state of ketosis may result in kidney stones and vitamin deficiencies. Regular health check-ups and consultation with healthcare professionals are essential for those considering prolonged adherence to a ketogenic lifestyle.


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Mag. Stephan Lederer, MSc.

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

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