The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet. 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 an increase of fat burn.
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.
Lack of energy and lethargy are common but disappear within two weeks. The ketogenic diet is not a balanced diet and only contains tiny portions of fresh fruit and vegetables, fortified cereals and calcium-rich foods. In particular, the B vitamins, calcium and vitamin D must be artificially supplemented. This is achieved by taking two sugar-free supplements designed for the patient’s age: a multivitamin with minerals, and calcium with vitamin D.
MCT oil – Normal dietary fat contains mostly long-chain triglycerides (LCT). Medium-chain triglycerides are more ketogenic than LCTs because they generate more ketones per unit of energy when metabolised. Their use allows for a diet with a lower proportion of fat and a greater proportion of protein and carbohydrate,leading to more food choices and larger portion sizes. The original MCT diet developed by Peter Huttenlocher in the 1970s derived 60% of its calories from MCT oil. Consuming that quantity of MCT oil caused abdominal cramps, diarrhoea and vomiting in some. A figure of 45% is regarded as a balance between achieving good ketosis and minimising gastrointestinal complaints. The classical and modified MCT ketogenic diets are equally effective and differences in tolerability are not statistically significant.
Modified Atkins – Compared with the ketogenic diet, the modified Atkins diet (MAD) places no limit on calories or protein, and the lower overall ketogenic ratio (approximately 1:1) does not need to be consistently maintained by all meals of the day.
The MAD requires less dietitian support than the ketogenic diet. Carbohydrates are initially limited to 15 g per day in adults, and increased to 20–30 g per day after a month or so. Like the ketogenic diet, the MAD requires vitamin and mineral supplements.
Low glycemic index – The low glycemic index treatment (LGIT) is an attempt to achieve the stable blood glucose levels as seen on the classic ketogenic diet while using a much less restrictive regime. The hypothesis is that stable blood glucose may be one of the mechanisms of action involved in the ketogenic diet, which occurs because the absorption of the limited carbohydrates is slowed by the high fat content. Although it is also a high-fat diet (with approximately 60% calories from fat), the LGIT allows more carbohydrate than either the classic ketogenic diet or the modified Atkins diet, approximately 40–60 g per day. However, the types of carbohydrates consumed are restricted to those that have a glycemic index lower than 50.
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