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Page last reviewed: 13/07/2011

Ketosis is a potentially serious condition that occurs when there are raised levels of chemicals called ketones in the blood.

Ketosis is often caused by a diet that is very low in carbohydrate. Carbohydrate is the main food group that is required by the body for producing energy, and it plays a key part in a healthy, balanced diet.

Fat metabolism

Carbohydrates are normally broken down into glucose, which is then converted into energy and transported to the body's muscles and organs.

However, if there is a lack of glucose, or if it is not possible for glucose to be broken down - for example, if your body does not produce enough insulin - the body will have to break down stored fat in order to convert it into energy. This is known as fat metabolism.

Fat metabolism causes a build-up of ketones in the blood, resulting in ketosis. Ketosis can occur during:

  • starvation
  • diabetes mellitus (type 1 diabetes)
  • alcoholism


As your body starts to break down fat rather than glucose, the levels of ketones in your blood will begin to rise. Ketones are acidic chemicals such as:

  • acetone
  • acetoacetate
  • beta-hydroxybutyrate

If left to build up, ketones can increase the acidity levels of your blood, which can affect your urine and may eventually cause serious damage to your liver and kidneys.

Your body may try to get rid of the excess amount of acetone through your lungs, which can give your breath a sweet, fruity smell that is sometimes mistaken for alcohol.


Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.


Glucose (or dextrose) is a type of sugar that is used by the body to produce energy.


Insulin is a hormone released by the pancreas that helps the body to control blood sugar levels.


Kidneys are a pair of bean-shaped organs located at the back of the abdomen. They remove waste and extra fluid from the blood and pass them out of the body as urine.


The liver is the largest organ in the body. Its main jobs are to secrete bile (to help digestion), detoxify the blood and change food into energy.

Page last reviewed: 13/07/2011

The ketogenic diet is high in fat, has an adequate amount of protein, and is low in carbohydrate. It was first designed in the early 1900s for treating children with epileptic seizures (fits).

Early research suggested that prolonged periods of fasting could help control severe epilepsy in children more effectively than the limited medication that was available at the time.

Since the ketogenic diet was first introduced, there have been significant advancements in the anticonvulsant medications that are used to control epileptic seizures in children.

However, in recent years, the ketogenic diet has been used successfully in cases where controlling seizures using medication has proven difficult.

How does the ketogenic diet work?

The ketogenic diet is a carefully controlled diet that works by stimulating the biochemical effects of starvation. The low amount of carbohydrate in the diet leads to the build-up of ketones in the blood, and it is the high levels of ketones that have been found to suppress epileptic seizures.

The calories that are consumed are restricted in accordance with the age and activity levels of the child. If calculated properly, the child will not lose or gain weight, but will be close to the ideal weight for their height and build.

For overweight children, calories are limited until their ideal weight is obtained. The diet must be supplemented with calcium and vitamins.

The ketogenic diet is an alternative treatment method for children who have epilepsy that is difficult to control using medication (in cases where the child has two or more epileptic seizures a week, despite using two or more appropriate anticonvulsant medications).

Medical supervision is required

The ketogenic diet should not be used without medical supervision, and its effects have not been adequately studied in adults or children under one year of age.

If you think your child could benefit from using a ketogenic diet to control their epileptic seizures, speak to your GP.

If you are trying to lose weight, ask your GP or a qualified dietitian for information about healthy eating and advice about how to lose weight safely.

Page last reviewed: 13/07/2011

If you are diabetic and do not take your insulin injections for a prolonged period of time, you may experience ketoacidosis.

Ketoacidosis is caused by uncontrolled diabetes mellitus (type 1 diabetes). It is a combination of ketosis (the build-up of ketones in the blood) and acidosis (increased blood acidity).

The lack of insulin means that your body will start to break down fats instead of glucose, leading to an increased production of ketones and raising the acidity level of your blood.

The symptoms of ketoacidosis include:

  • loss of appetite
  • nausea
  • vomiting
  • the need to urinate frequently (polyuria)
  • high temperature
  • stomach pain
  • a fruity smell on your breath, which may smell like pear drops or nail varnish

If left untreated, ketoacidosis will lead to coma and, eventually, death. Therefore, the condition must be treated as a medical emergency. Seek immediate medical attention if you have the above symptoms.

You may need to be admitted to hospital in order to receive intravenous fluids (administered directly into a vein), as well as insulin and glucose. Dietary changes may also be recommended.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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