The ketogenic diet aims to induce ketosis to burn more body fat. In immediate periods of ketosis, a person may experience increased thirst, muscle cramps, and headaches.

Ketosis is a metabolic process that occurs when the body begins to burn fat for energy because it does not have enough carbohydrates to burn. During this process, the liver produces chemicals called ketones.

The ketogenic, or keto, diet aims to induce ketosis in order to burn more fat. Proponents of the ketogenic diet claim that it boosts weight loss and improves overall health.

According to one 2018 study, people following a “well-formulated” ketogenic diet typically eat less than 50 grams (g) of carbohydrates per day and around 1.5 g of protein per kilogram of body weight.

Despite these guidelines, some people following the diet may not know when they are in ketosis.

In this article, we list 10 signs of ketosis that may help a person determine whether the ketogenic diet is working for them.

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Having ketones in the blood is probably the most definitive sign that someone is in ketosis. Doctors may also use urine and breath tests to check for ketone levels, but these are less reliable than blood samples.

A special home testing kit allows people to measure their own blood ketone levels. Or, a doctor may take a blood sample and send it away for testing. When a person is in nutritional ketosis, they will have blood ketone levels of 0.5–3 millimoles per liter.

Alternatively, people can use a breath analyzer to test for ketones in their breath, or they may use indicator strips to check their urinary levels.

Some research suggests that this type of very low-carbohydrate diet is effective for weight loss. Therefore, people should expect to lose some weight when in ketosis.

The results of a 2013 meta-analysis that examined the findings from several randomized controlled trials suggest that people following a ketogenic diet may lose more weight in the long term than people following a low-fat diet.

People on a ketogenic diet may notice weight loss in the first few days, but this is typically just a reduction in water weight. True fat loss may not occur for several weeks.

Ketosis may cause some people to feel thirstier than usual, which may occur as a side effect of water loss. However, high levels of ketones in the body can also lead to dehydration and an electrolyte imbalance. Both of these reactions can cause complications.

Research into ketogenic diets for sports performance lists dehydration as a side effect of ketosis. Athletes may also have a higher risk of kidney stones, which is a complication of dehydration.

To avoid dehydration, drink plenty of water and other liquids. See a doctor if symptoms of dehydration, such as extreme thirst or dark-colored urine, occur.

Dehydration and electrolyte imbalances can cause muscle cramps. Electrolytes are substances that carry electrical signals between the body’s cells. Imbalances in these substances lead to disrupted electrical messages that may cause muscle contractions and spasms.

People following the ketogenic diet should ensure that they are getting enough electrolytes from the food they eat to avoid muscle pains and other symptoms of an imbalance.

Electrolytes include calcium, magnesium, potassium, and sodium. A person can get these from eating a balanced diet. However, if symptoms persist, a doctor may recommend supplements or other dietary changes.

Headaches can be a common side effect of switching to a ketogenic diet. They may occur as a result of consuming fewer carbohydrates, especially sugar. Dehydration and electrolyte imbalances can also cause headaches.

Ketosis headaches typically last from 1 day to 1 week, although some people may experience pain for longer. See a doctor if headaches persist.

Interestingly, some recent research suggests the ketogenic diet as a potential treatment for migraines and cluster headaches.

For example, a 2017 study proposes the diet for people with episodic and chronic migraine. Also, one 2018 study suggests the ketosis diet as a possible treatment for those with drug-resistant cluster headaches.

However, more research is necessary to confirm the diet’s effectiveness for treating or preventing these types of headaches.

In the initial stages of a ketosis diet, people may feel more tired and weaker than usual. This fatigue occurs as the body switches from burning carbohydrates to burning fat for energy. Carbohydrates provide a quicker burst of energy to the body.

A small 2017 study involving athletes found tiredness to be a common side effect of the ketosis diet. Participants typically observed this during the first few weeks.

After several weeks on the diet, people should notice an increase in their energy levels. If not, they should seek medical attention, as fatigue is also a symptom of dehydration and nutrient deficiencies.

Making any dietary changes can raise the risk of stomach upset and other digestive complaints. This may also occur when a person switches to the ketogenic diet.

To reduce the risk of experiencing stomach complaints, drink plenty of water and other fluids. Eat non-starchy vegetables and other fiber-rich foods to alleviate constipation, and consider taking a probiotic supplement to encourage a healthy gut.

Following a ketogenic diet may disrupt a person’s sleeping habits. Initially, they may experience difficulty falling asleep or nighttime waking. These symptoms typically go away within a few weeks.

Bad breath is among the most common side effects of ketosis. This is because ketones leave the body through the breath as well as the urine. People on the diet, or those around them, may notice that their breath smells sweet or fruity.

A ketone called acetone is usually responsible for the odor, but other ketones, such as benzophenone and acetophenone, may also contribute to bad breath.

There is no way to reduce ketosis breath, but it may improve with time. Some people use sugar-free gum or brush their teeth several times per day to mask the smell.

Initially, the ketogenic diet may cause headaches and concentration difficulties. However, these symptoms should fade over time. People following a long-term ketogenic diet often report better clarity and focus, and some research supports this.

According to the results of a 2018 systematic review, people with epilepsy who follow the ketogenic diet report better alertness and attention. Also, these people showed greater alertness in some cognitive tests.

Other studies suggest that the ketogenic diet may enhance cognitive function and provide neuroprotective effects.

What does ketosis feel like?

When the body first enters ketosis, some people may experience what is known as ‘keto flu‘. A person may feel nauseous, fatigued, dizzy, and constipated. However, anecdotal reports suggest ketosis could be linked with feelings of well-being and mild euphoria.

How long do ketosis symptoms last?

Symptoms of ketosis may last for a few days but could persist for up to a few weeks.

People in ketosis may experience a variety of side effects and symptoms, including headaches, stomach upset, and changes to their sleep and energy levels.

For a more accurate way of determining ketosis, people can check the levels of ketones in their blood, breath, or urine.

Those who wish to try a ketogenic diet should always speak to their doctor first, as a very low-carbohydrate diet may not be suitable for everyone. It is also vital to seek medical advice for persistent or severe symptoms of ketosis.

It is worth noting that researchers run most scientific studies into the ketogenic diet for less than a year, so the long-term health outcomes are not yet fully known.