10 Signs and Symptoms of Ketosis

The ketogenic diet deprives your body of carbohydrates, which results in ketosis — a metabolic state where your body burns ketones for fuel (1).

Sustained ketosis can help you attain weight loss and reduce feelings of hunger, among other benefits supported by various research studies (2)(3)(4).

However, entering ketosis for the first time may cause you to experience both positive and negative symptoms like headaches, bad breath, and stomach upset. These indicate that your glycogen levels have dropped and your ketone levels have increased.

Signs and Symptoms of Ketosis

Below are the ten common signs and symptoms that suggest you’re in ketosis, and what you can do.

1. Bad Breath

A lot of people in ketosis get bad breath, also known as “keto breath” as it has a distinct fruity-smelling odor.

Some may even describe it as nail polish, and this is due to the production of acetone, one of the ketones in ketosis. Your body expels acetone through the breath (5).

The good news is that bad breath goes away after some time as keto adaptation occurs — meaning, your body is now more capable of using ketones for energy.

In the meantime, you can reduce ketosis breath by chewing on a sugar-free gum, especially in social situations. Also, make sure to brush your teeth multiple times daily and stay hydrated with lots of water.

2. Weight Loss

Studies show that following a keto diet can lead to rapid and sustained weight loss (6)(7).

When it comes to rapid weight loss, a person can expect to lose a lot of water weight at the start of their diet. Reducing carbs leads to a reduction of glycogen stores, and glycogen happens to be bound to water (8).

This initial water weight loss will be followed by a loss of body fat as long as you adhere to the diet while also paying attention to your macros and calorie needs, which may change over time.

Since losing water can increase your risk of electrolyte losses such as potassium, consider replenishing electrolytes through a nutrient-dense keto diet. Taking electrolyte supplements also helps to effectively restore lost electrolytes.

3. Increased Ketone Levels in Blood, Breath, and Urine

The best way to tell whether you’re in ketosis or not is to measure ketones, which are present in your blood, breath, and urine.

Testing blood ketones is the most accurate method because it checks levels of beta-hydroxybutyrate (BHB), the most abundant ketone in mammals (9). However, a downside is that blood ketone testing may cause discomfort since it involves pricking and drawing blood, and devices can be costly.

Urine testing is a more convenient and affordable approach. It entails using over-the-counter reagent strips that change color when passed through a stream of urine. In a study done on subjects with stable ketosis, researchers have found that urine test results are more reliable in the early morning and after dinner time (10).

Breath testing is also easy and cost-effective. It specifically measures acetone, the third and least abundant ketone body (11)(12).

Note that if you’re diagnosed with diabetes, your doctor may recommend testing your ketone levels more than once daily.

4. Decreased Hunger

There’s evidence that a keto diet reduces or prevents hunger, causing a person to lose weight. However, the exact mechanisms behind this decreased hunger still needs more research.

Some recent findings suggest that the keto diet suppresses the hunger hormone ghrelin while also increasing satiety. In one review, it was found that consuming a ketone ester drink reduced hunger and increased satiety compared to a glucose drink (13)(14).

In other words, ketones as an energy source are better for controlling hunger than glucose.

Thus, taking advantage of nutritional ketosis can be beneficial for those who are looking to keep off the weight long term.

5. Increased Focus and Energy

You may read about the positive effects of the keto diet on brain health, cognitive performance, and sustained energy (15)(16).

But when you enter ketosis as a beginner, you’re likely to experience low energy levels and brain fog, even irritability and headaches. These symptoms are expected to last for a few days to weeks until your body adjusts to its new fuel source — ketones.

In times of low insulin, ketones can meet most of your tissues’ basal energy requirements up to 50%, while they can meet up to 70% of your brain’s energy requirements (17).

Research shows that ketones don’t just serve as an alternative fuel, but they also offer protection in both normal and injured brains (17).

To achieve better focus and energy on keto sooner, consider speeding up the adaptation process by keeping carbohydrates low, exercising, or intermittent fasting (or all of the above).

6. Short-Term Weakness and Fatigue

Weakness and fatigue are common symptoms of ketosis for new dieters, but they last only for a while. You may feel more tired than usual, and struggle to perform most of your activities without feeling the urge to take breaks.

If you’ve been used to getting most of your calories from high-carb foods, it’s normal to experience a loss of energy as a side effect.

Sometimes, tiredness can also result from water losses (glycogen depletion) and electrolyte losses as part of the keto flu (18).

While these symptoms eventually subside, make sure to allow yourself to get lots of rest. If you’re struggling to follow your usual workout, go for a lighter workout such as walking outside, swimming, or doing simple house chores.

7. Digestive Issues

Changing your macros, such as increasing your dietary fat and protein, can trigger diarrhea or constipation. These digestive issues are normal and subside over time as your body becomes more effective in their breakdown and absorption.

Some people have more trouble digesting fat than others and may benefit by taking digestive enzymes. Furthermore, it’s important to cut back on the bad fats and prioritize healthy fats instead.

In addition, consider increasing your fiber intake by incorporating low-carb vegetables in every meal to help relieve constipation. Examples of keto-friendly veggies include spinach, lettuce, cucumbers, and other leafy greens.

To help prevent other gut problems like gas and bloating, you might want to avoid consuming sugar alcohols commonly found in a lot of keto snacks.

8. Difficulty Sleeping

Insomnia is another possible consequence of reducing carbs and increasing your fat and protein. Aside from this macronutrient shift, keto flu symptoms can also make it difficult for you to sleep soundly at night (19).

It also helps to note other things that could be interfering with sleep that aren’t keto related. Things like stress, illness, tea, caffeine, room temperature, and noise can impact sleep (20).

If you’re struggling with insomnia, take simple steps such as putting away your devices before bed time, following a consistent sleep schedule, and avoiding caffeine later during the day.

There are also low-carb foods that promote a good night’s sleep, such as fatty fish, almonds, and lettuce. Include these in your keto diet shopping list and daily meals.

More importantly, know that insomnia goes away, and you’ll start experiencing the effect of keto on improving sleep quality (20).

9. Flu-like Symptoms

The keto flu or carb flu is a collection of symptoms such as nausea, vomiting, muscle cramps, muscle soreness, increased sugar or carb cravings, and irritability.

Along with other signs and symptoms listed above, the keto flu is common during the initial stages of ketosis. Usually, keto flu starts a few days after doing keto. Symptoms may last up to a week (or longer) depending on the person.

Strategies like taking electrolytes, getting adequate sleep, and increasing your fat intake can help improve your symptoms so you’ll feel better (21)(22).

10. Decreased Exercise Performance

Exercising depletes your glycogen stores, allowing you to enter ketosis faster.

However, during the first few days of ketosis, you’ll likely feel the need to scale back on your workouts due to increased tiredness and fatigue.

Study shows that keto-adaptation improves your exercise endurance (23). But until that happens, in the meantime, make adjustments to your routine. Don’t overexert yourself.

The Bottom Line

These are the signs and symptoms common in people who are new to ketosis. Note that each person may experience them differently, and that the time it takes to enter ketosis varies as well.

Knowing these temporary ketosis side effects allows you to plan ahead. You might need to adjust your schedule and habits to help ease negative signs and symptoms.

And if you’re diagnosed with a medical condition like diabetes, be sure to get support from a health professional.

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Evidence based

This article is based on scientific evidence, written and reviewed by experts.

The founders of Ketogenic Buddies are health care professionals. As we grow, we include other qualified subject matter experts as part of our content team.

This article contains scientific references. The numbers in the parentheses (1, 2, 3) are clickable links to peer-reviewed scientific papers.