A ketogenic diet, or keto diet, is a very low carbohydrate eating plan that forces the body to use fat rather than glucose as a primary energy source. When you follow the plan, you build meals around fatty foods and significantly restrict your intake of carbohydrates and protein. As a result of that macronutrient balance, acids called ketones are produced in the body. When ketone levels are high enough, the dieter is in a state of ketosis.
On the ketogenic diet, carbohydrates are restricted and so cannot provide for all the metabolic needs of the body. Instead, fatty acids are used as the major source of fuel. These are used through fatty-acid oxidation in the cell's mitochondria (the energy-producing parts of the cell). Humans can convert some amino acids into glucose by a process called gluconeogenesis, but cannot do this by using fatty acids. Since amino acids are needed to make proteins, which are essential for growth and repair of body tissues, these cannot be used only to produce glucose. This could pose a problem for the brain, since it is normally fuelled solely by glucose, and most fatty acids do not cross the blood–brain barrier. However, the liver can use long-chain fatty acids to synthesise the three ketone bodies β-hydroxybutyrate, acetoacetate and acetone. These ketone bodies enter the brain and partially substitute for blood glucose as a source of energy.
In the 1960s, it was discovered that medium-chain triglycerides (MCTs) produce more ketone bodies per unit of energy than normal dietary fats (which are mostly long-chain triglycerides). MCTs are more efficiently absorbed and are rapidly transported to the liver via the hepatic portal system rather than the lymphatic system. The severe carbohydrate restrictions of the classic ketogenic diet made it difficult for parents to produce palatable meals that their children would tolerate. In 1971, Peter Huttenlocher devised a ketogenic diet where about 60% of the calories came from the MCT oil, and this allowed more protein and up to three times as much carbohydrate as the classic ketogenic diet. The oil was mixed with at least twice its volume of skimmed milk, chilled, and sipped during the meal or incorporated into food. He tested it on twelve children and adolescents with intractable seizures. Most children improved in both seizure control and alertness, results that were similar to the classic ketogenic diet. Gastrointestinal upset was a problem, which led one patient to abandon the diet, but meals were easier to prepare and better accepted by the children. The MCT diet replaced the classic ketogenic diet in many hospitals, though some devised diets that were a combination of the two.
Ketogenic diets are very, very powerful, metabolically speaking and this is especially important if you take any kind of medication for blood pressure, diabetes, cholesterol or triglycerides. The amount taken of these medications will most likely need to be sharply reduced while on a ketogenic diet to avoid negative effects such as excessively low blood sugar or blood pressure.
You may also want to buy some Ketostix Reagent Strips so that you can check to see if you are in ketosis for the first few weeks. However, after the first 3-4 weeks on the plan, the goal is to become "keto-adapted". Once adapted, the body should be burning the ketones for fuel. The stick shouldn't register as deep purple if you are using the ketones as a fuel source. And they now have blood ketone meters available to track blood ketones at home. This is a much more accurate way to track your individual ketone levels. See my ketosis page for more information.
When you eat foods high in carbohydrates and fat, your body naturally produces glucose. Carbohydrates are the easiest thing for the body to process, and therefore it will use them first – resulting in the excess fats to be stored immediately. In turn, this causes weight gain and health problems that are associated with high fat, high carbohydrate diets (NOT keto).