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What is ketosis, and is it healthy?

Definition, benefits, downsides, and more

Ketosis is a natural metabolic state that your body enters when following a very low carb diet or during starvation. This article explores ketosis and health.

This article is based on scientific evidence, written by experts, and fact-checked by experts.
We look at both sides of the argument and strive to be objective, unbiased, and honest.
Ketosis: Definition, benefits, downsides, and more
Last updated on July 9, 2023, and last reviewed by an expert on June 26, 2022.

Ketosis is an elevation of ketone levels in the body. Ketone production is increased in several situations, including when you follow a very low-carb diet.

Ketosis: Definition, benefits, downsides, and more

Normally, your body prefers to use blood sugar, also called glucose, for energy. However, during ketosis, your body gets more of its energy from ketones, which are produced from fat.

While research is mixed, ketosis may have several health benefits, such as fewer seizures in children with epilepsy, weight loss, and improved blood sugar management.

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Nevertheless, the diet can be difficult to follow and may not be suitable for everyone. As such, you may wonder whether you should try it.

This article explains all you need to know about ketosis, its purported benefits, downsides, and risks.

In this article

What is ketosis?

Ketosis is a metabolic state in which your blood has a high concentration of ketones, namely beta-Hydroxybutyrate.

It occurs when your body starts using fat as its main fuel source due to limited access to glucose, or blood sugar, typically caused by starvation, fasting, or following a very low carb diet.

Many cells in the body prefer using glucose for fuel. When your body doesn’t have enough glucose to power these cells, levels of the hormone insulin decrease, causing fatty acids to be released from body fat stores in large amounts.

Many of these fatty acids are transported to the liver, where they’re oxidized and turned into ketones, also called ketone bodies. These are then used as an alternative energy source throughout the body.

Unlike fatty acids, ketones can cross the blood-brain barrier and provide energy for your brain in the absence of glucose.

Summary: Ketosis is a metabolic state in which ketones become an important source of energy for the body and brain. It occurs when carb intake and insulin levels are low.

Ketosis and the ketogenic diet

To enter a state of ketosis, you may need to eat fewer than 50 grams of carbs per day, sometimes as little as 20 grams. The exact carb intake that will cause ketosis varies by individual.

To achieve this, you need to remove or greatly reduce most carbohydrate-rich foods from your diet, including:

To put this into perspective, 1 slice (32 grams) of bread contains roughly 15 grams of carbs, while 1 cup (186 grams) of cooked rice contains around 53 grams of carbs.

How long does it take to enter ketosis?
Suggested read: How long does it take to enter ketosis?

People may choose to follow a keto diet to lose weight, better manage their blood sugar levels, or reduce the incidence of epilepsy-related seizures, among other reasons.

Summary: You can achieve ketosis by eating no more than 20–50 grams of carbs per day. This is commonly known as a ketogenic diet.

Common signs and symptoms of ketosis

If you’re intentionally following a ketogenic diet, you may wonder whether you’ve achieved ketosis. Here are some common signs and symptoms:

It’s common for a person new to ketosis to experience a myriad of symptoms known as the keto flu, such as headache, tiredness, nausea, and stomach upset.

To know for certain that you’re in ketosis, it’s best to check your blood ketone levels using a urine or blood measurer. You’ve achieved ketosis if your blood ketones are between 0.5–3.0 millimoles per liter (mmol/L).

Summary: Common symptoms of ketosis include bad breath, weight loss, reduced appetite, and temporary fatigue or brain fog. Testing your blood ketone levels is the best way to know for certain.

Health benefits of ketosis

There are some potential health benefits to being in ketosis, especially long-term. Still, it’s worth noting that not all experts agree, and many call for higher quality research.


Epilepsy is a brain disorder characterized by recurring seizures. It’s a neurological condition and affects around 50 million people worldwide.

Most people with epilepsy use medications to manage their seizures, although this treatment option is ineffective in around 30% of people.

Suggested read: Is ketosis safe and does it have side effects?

In the early 1920s, the ketogenic diet was introduced as a treatment for epilepsy in those who didn’t respond to drug treatment.

The diet has primarily been used in children. Many studies in both children and adults with epilepsy have found that it can significantly reduce seizures and sometimes even cause remission.

That said, the diet is difficult to follow long-term and is usually reserved for people who don’t respond to conventional treatments.

Weight loss

In recent years, the ketogenic diet has soared in popularity for its potential to promote weight loss.

When eating a very low-carb diet, your body relies on fat-derived ketones produced in the liver to fuel itself. Over time, this can lead to meaningful weight and fat loss.

What’s more, people tend to feel less hungry and more full on a ketogenic diet, which is attributed to ketosis. For this reason, it’s generally unnecessary to count calories when following the diet.

However, it’s widely recognized that strict adherence is critical for long-term success. Some individuals may find it easy to stick to the ketogenic diet, while others may find it unsustainable.

It’s also worth noting that some research suggests that the keto diet might not be the best way to lose weight.

For example, one review concluded that it didn’t promote weight loss more than other diets. Furthermore, they found that it likely doesn’t have specific advantages for people with metabolic disorders like diabetes.

Type 2 diabetes

Following the ketogenic diet may benefit those with diabetes.

Research has shown that following a ketogenic diet is an effective strategy for managing blood sugar levels in those with type 2 diabetes.

It may also be effective for those with type 1 diabetes.

But again, adhering to the ketogenic diet may be difficult long term, so it may not be a suitable strategy for many people with this condition. Additionally, it could put you at greater risk of hypoglycemia, or low blood sugar levels.

Ultimately, it’s important to work closely with a healthcare professional. They can help you find a way to manage your diabetes that suits your health, lifestyle, and preferences.

Suggested read: How many carbs should you eat if you have diabetes?

Summary: The ketogenic diet may be an effective strategy to manage epilepsy, type 2 diabetes, and weight. However, the diet is difficult to follow long term and may not be suitable for everyone.

Downsides and risks of ketosis

While a ketogenic diet may provide some benefits, it can also trigger several side effects and is not suitable for everyone.

Short-term side effects include headache, fatigue, constipation, dehydration, and bad breath. These usually disappear within a few days or weeks of starting the diet.

The diet is also associated with a risk of developing kidney stones, high LDL (bad) cholesterol, and nutrient deficiencies.

What’s more, because the diet is highly restrictive, it may not be suitable for those with a history of disordered eating. Also, following such a strict diet can feel socially isolating for some, since food options are often limited in social settings.

It’s likewise important to note that there have been reports of ketoacidosis, a potentially life-threatening condition, in breastfeeding mothers who follow a low carb or keto diet. If you’re breastfeeding, speak with a healthcare professional before trying this diet.

People who are taking hypoglycemic, or blood-sugar-lowering drugs, should also consult a healthcare professional before trying a ketogenic diet, as it may reduce their need for medication.

Sometimes ketogenic diets are low in fiber. For this reason, it’s a good idea to eat plenty of high-fiber, low-carb vegetables to maintain good digestive health and prevent constipation.

Finally, while some people enjoy the ketogenic diet, it’s not necessary for most people. You don’t need to try the diet to lose weight or manage your diabetes if you don’t want to.

If you’re interested in switching to a very low-carb diet, consult a healthcare professional first in case it’s not suitable for you.

Summary: The ketogenic diet is not appropriate or safe for everyone. Before starting a ketogenic diet, be sure to consult your healthcare provider.

Ketosis vs. ketoacidosis

People often confuse ketosis and ketoacidosis.

While ketosis is a normal part of your metabolism, ketoacidosis is a dangerous metabolic condition that can be fatal if left untreated.

In ketoacidosis, the bloodstream is flooded with extremely high levels of glucose and ketones. This makes the blood acidic, which is life-threatening.

Ketoacidosis is most often associated with uncontrolled type 1 diabetes. It can also occur in those with type 2 diabetes or severe alcohol abuse.

Symptoms of ketoacidosis include but are not limited to:

If you’re experiencing any of these symptoms, seek immediate medical attention.

Suggested read: The ketogenic diet: A detailed beginner's guide to keto

Summary: Ketosis is a natural metabolic state caused by consuming a very low-carb diet, while ketoacidosis is a life-threatening medical emergency that requires immediate medical attention.


Ketosis is a metabolic state that you can achieve by following a ketogenic diet.

Possible benefits of ketosis include weight loss, improved blood sugar management, and reduced seizures in children with epilepsy.

However, following a strict ketogenic diet to induce ketosis can be difficult and lead to unwanted short-term side effects like headaches, stomach upset, dehydration, and bad breath.

Long-term side effects may include kidney stones, increased LDL (bad) cholesterol, and nutrient deficiencies.

While the ketogenic diet can be enjoyable and beneficial for some people, it may not be for others. Therefore, speak with a healthcare professional before trying it.

Quick tip

If you’re interested in trying the ketogenic diet, schedule an appointment with a registered dietitian or another healthcare professional who can help you weigh the pros and cons to determine whether it’s right for you.

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