What is the Ketogenic Diet?

The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet primarily used to treat difficult-to-control (refractory) epilepsy in children. The diet mimics aspects of starvation by forcing the body to burn fats rather than carbohydrates. Normally, the carbohydrates contained in food are converted into glucose, which is then transported around the body and is particularly important in fuelling brain function. However, if there is very little carbohydrate in the diet, the liver converts fat into fatty acids and ketone bodies. The ketone bodies pass into the brain and replace glucose as an energy source. An elevated level of ketone bodies in the blood, a state known as ketosis, leads to a reduction in the frequency of epileptic seizures.

The diet provides just enough protein for body growth and repair, and sufficient calories to maintain the correct weight for age and height. The classic ketogenic diet contains a 4:1 ratio by weight of fat to combined protein and carbohydrate. This is achieved by excluding high-carbohydrate foods such as starchy fruits and vegetables, bread, pasta, grains and sugar, while increasing the consumption of foods high in fat such as cream and butter.

Most dietary fat is made of molecules called long-chain triglycerides (LCTs). However, medium-chain triglycerides (MCTs)—made from fatty acids with shorter carbon chains than LCTs—are more ketogenic. A variant of the diet known as the MCT ketogenic diet uses a form of coconut oil, which is rich in MCTs, to provide around half the calories. As less overall fat is needed in this variant of the diet, a greater proportion of carbohydrate and protein can be consumed, allowing a greater variety of food choices.

Developed in the 1920s, the ketogenic diet was widely used into the next decade, but its popularity waned with the introduction of effective anticonvulsant drugs. In the mid 1990s, Hollywood producer Jim Abrahams, whose son's severe epilepsy was effectively controlled by the diet, created the Charlie Foundation to promote it. Publicity included an appearance on NBC's ''Dateline'' programme and ''...First Do No Harm'' (1997), a made-for-television film starring Meryl Streep. The foundation sponsored a multicentre research study, the results of which—announced in 1996—marked the beginning of renewed scientific interest in the diet.

The diet is effective in half of the patients who try it, and very effective in one third of patients. In 2008, a randomised controlled trial showed a clear benefit for treating refractory epilepsy in children with the ketogenic diet. There is some evidence that adults with epilepsy may benefit from the diet, and that a less strict regime, such as a modified Atkins diet, is similarly effective. The ketogenic diet has also been proposed as a treatment for a number of neurological conditions other than epilepsy; as of 2008, research in this area has yet to produce sufficient positive data to warrant clinical use.

The ketogenic diet is a medical nutrition therapy that involves participants from various disciplines. Team members include a registered paediatric dietitian who coordinates the diet programme; a paediatric neurologist who is experienced in offering the ketogenic diet; and a registered nurse who is familiar with childhood epilepsy. Additional help may come from a medical social worker who works with the family and a pharmacist who can advise on the carbohydrate content of medicines. Lastly, the parents and other caregivers must be educated in many aspects of the diet in order for it to be safely implemented.

Initiation

The Johns Hopkins Hospital protocol for initiating the ketogenic diet has been widely adopted. It involves a consultation with the patient and their caregivers and, later, a short hospital admission. Because of the risk of complications during ketogenic diet initiation, most centres begin the diet under close medical supervision in hospital.

At the initial consultation, patients are screened for conditions that may contraindicate the diet. A dietary history is obtained and the parameters of the diet selected: the ketogenic ratio of fat to combined protein and carbohydrate, the calorie requirements, and the fluid intake.

The day before admission to hospital, the proportion of carbohydrate in the diet may be decreased and the patient begins fasting after his or her evening meal. On admission, only calorie- and caffeine-free fluids are allowed until dinner, which consists of "eggnog" restricted to one-third of the typical calories for a meal. The following breakfast and lunch are similar, and on the second day, the "eggnog" dinner is increased to two-thirds of a typical meal's caloric content. By the third day, dinner contains the full calorie quota and is a standard ketogenic meal (not "eggnog"). After a ketogenic breakfast on the fourth day, the patient is discharged. Where possible, the patient's current medicines are changed to carbohydrate-free formulations.

When in the hospital, glucose levels are checked several times daily and the patient is monitored for signs of symptomatic ketosis (which can be treated with a small quantity of orange juice). Lack of energy and lethargy are common but disappear within two weeks. The parents attend classes over the first three full days, which cover nutrition, managing the diet, preparing meals, avoiding sugar and handling illness. The level of parental education and commitment required is higher than with medication.

Variations on the Johns Hopkins protocol are common. The initiation can be performed using outpatient clinics rather than requiring a stay in hospital. Often there is no initial fast (fasting increases the risk of acidosis and hypoglycaemia and weight loss). Rather than increasing meal sizes over the three-day initiation, some institutions maintain meal size but alter the ketogenic ratio from 2:1 to 4:1.

For patients who benefit, half achieve a seizure reduction within five days (if the diet starts with an initial fast of one to two days), three-quarters achieve a reduction within two weeks, and 90% achieve a reduction within 23 days. If the diet does not begin with a fast, the time for half of the patients to achieve an improvement is longer (two weeks) but the long-term seizure reduction rates are unaffected. Parents are encouraged to persist with the diet for at least three months before any final consideration is made regarding efficacy.

Maintenance

After initiation, the child regularly visits the hospital outpatient clinic where they are seen by the dietitian and neurologist, and various tests and examinations are performed. These are held every three months for the first year and then every six months thereafter. Infants under one year old are seen more frequently, with the initial visit held after just two to four weeks. A period of minor adjustments is necessary to ensure consistent ketosis is maintained and to better adapt the meal plans to the patient. This fine-tuning is typically done over the telephone with the hospital dietitian and includes changing the number of calories, altering the ketogenic ratio, or adding some MCT or coconut oils to a classic diet. Urinary ketone levels are checked daily to detect whether ketosis has been achieved and to confirm that the patient is following the diet, though the level of ketones does not correlate with an anticonvulsant effect. This is performed using ketone test strips containing nitroprusside, which change colour from buff-pink to maroon in the presence of acetoacetate (one of the three ketone bodies).

A short-lived increase in seizure frequency may occur during illness or if ketone levels fluctuate. The diet may be modified if seizure frequency remains high, or the child is losing weight. Loss of seizure-control may come from unexpected sources. Even "sugar-free" food can contain carbohydrates such as maltodextrin, sorbitol, starch and fructose. The sorbitol content of suntan lotion and other skincare products may be high enough for some to be absorbed through the skin and thus negate ketosis.

Discontinuation

About 10% of children on the ketogenic diet achieve freedom from seizures, and many are able to reduce the use of anticonvulsant drugs or eliminate them altogether. Traditionally, at around two years on the diet, or after six months of being seizure-free, the diet may be gradually discontinued over two or three months. This is done by lowering the ketogenic ratio until urinary ketosis is no longer detected, and then lifting all calorie restrictions. This timing and method of discontinuation mimics that of anticonvulsant drug therapy in children, where the child has become seizure free. When the diet is required to treat certain metabolic diseases, the duration will be longer. The total diet duration is up to the treating ketogenic diet team and parents; durations up to 12 years have been studied and found beneficial.

Children who discontinue the diet after achieving seizure freedom have about a 20% risk of seizures returning. The length of time until recurrence is highly variable but averages two years. This risk of recurrence compares with 10% for resective surgery (where part of the brain is removed) and 30–50% for anticonvulsant therapy. Of those that have a recurrence, just over half can regain freedom from seizures either with anticonvulsants or by returning to the ketogenic diet. Recurrence is more likely if, despite seizure freedom, an electroencephalogram (EEG) shows epileptiform spikes, which indicate epileptic activity in the brain but are below the level that will cause a seizure. Recurrence is also likely if an MRI scan shows focal abnormalities (for example, as in children with tuberous sclerosis). Such children may remain on the diet longer than average, and it has been suggested that children with tuberous sclerosis who achieve seizure freedom could remain on the ketogenic diet indefinitely.

The ketogenic diet may be a successful treatment for several rare metabolic diseases. Case reports of two children indicate that it may be a possible treatment for astrocytomas, a type of brain tumour. Autism, depression, migraine headaches, polycystic ovary syndrome, and type 2 diabetes mellitus have also been shown to improve in small case studies. There is evidence from uncontrolled clinical trials and studies in animal models that the ketogenic diet can provide symptomatic and disease-modifying activity in a broad range of neurodegenerative disorders including amyotrophic lateral sclerosis, Alzheimer's disease and Parkinson's disease, and may be protective in traumatic brain injury and stroke. Because tumour cells are inefficient in processing ketone bodies for energy, the ketogenic diet has also been suggested as a treatment for cancer. , there is insufficient evidence to support the use of the ketogenic diet as a treatment for these conditions; however, clinical trials for many of them are ongoing.

In March 2009, caprylidene (Axona) was approved as a medical food by the US Food and Drug Administration for the "dietary management of the metabolic processes and nutritional requirements associated with mild to moderate Alzheimer's disease". Glucose metabolism by the brain is impaired in Alzheimer's disease, and it is proposed that ketone bodies may provide an alternative energy source. Caprylidene is a powdered form of the MCT caprylic triglyceride.

Further Reading


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Comments
  1. Cleusa Nogueira de Castro Cleusa Nogueira de Castro Brazil says:

    Achei muito interessante essa dieta e pretendo me aprofundar no estudo dela, pois tenho urgência em adotá-la para pessoa de minha família.

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