Classical & MCT Ketogenic Diets (Traditional Diets)

A high fat, low carbohydrate diet was first described in the medical literature in 1921 as a treatment for epilepsy in children, following other reports of the beneficial effects of fasting on seizure control. The diet was designed to mimic the metabolic changes that occur in the body during starvation, i.e. adaption to spare muscle protein breakdown and draw on energy reserves of body fat. Muscles and other tissues progressively switch energy source from glucose to free fatty acids which are converted to ketone bodies (acetoacetate and b-hydroxybutyrate); these become the primary energy substrate for brain and other metabolically active tissues in the absence of adequate glucose supply. This state of ketosis is characterized by the rising levels of ketone bodies which can be measured in the blood or urine. The diet became known as the ‘ketogenic diet’ and is the basis of the classical ketogenic diet still used today.

This classical diet is based on a ratio of ketone producing foods in the diet (fat) to foods that reduce ketone production (carbohydrate and protein). A ‘ketogenic’ ratio of at least 3:1 is usually needed for maintenance of a good state of ketosis and optimal seizure control, although this varies between individuals and some will need a lower 2:1 ratio or a higher 4:1 ratio. In a 3:1 diet, 87% of the energy is provided by fat, in a 4:1 diet this increases to 90%. Fat is usually provided from food sources such as butter, mayonnaise, margarine, oil, cream, or a supplement that is available on medical prescription. Protein intake is based on minimum requirements for growth and is generally provided by a high-biological value source at each meal such as meat, fish, eggs or cheese. Carbohydrate is very restricted; starchy foods are not allowed, the main sources being a limited portion of vegetables or fruit.

The medium chain triglyceride (MCT) ketogenic diet was developed in the 1970s as an alternative to the classical diet. MCT is absorbed and transported more efficiently in the body than other types of fat and will yield more ketones per unit of dietary energy. Therefore less total fat is needed on the MCT diet allowing more protein and carbohydrate food sources to be included. The traditional MCT diet provided a higher amount of energy from MCT however led to reports of gastro-intestinal problems in some children, and a modified version with less MCT was suggested. In practice a starting MCT level is now chosen that will allow good ketosis but avoid risk of side effects; this can be increased as needed and tolerated. MCT should be included in all meals and snacks; this is provided from an oil or emulsion, both available on medical prescription. The remaining energy in the MCT diet is provided from carbohydrate, protein and fat from foods. Larger portions of carbohydrate and protein will allow increased choice. A randomized controlled trial of both classical and MCT ketogenic diets was reported in 2009 and did not find either type of diet to be significantly better in terms of efficacy or tolerability, concluding both diets have their place in the treatment of childhood epilepsy.

Both the classical and MCT ketogenic diet involve strict dietary calculation and weighing of all foods. The dietitian will calculate an individual diet prescription, based on energy and protein requirements. This is likely to be started at a lower ratio or MCT content and built up over a few days as tolerated. From this prescription, recipes can be developed; this is usually done using a computer program. Exchange lists may be used as an alternative means to implement the prescription; this method is commonly used in the MCT diet. Vitamin and mineral supplementation will be needed with classical and MCT ketogenic diets due to their restrictions; this will be prescribed by the dietitian after assessment of individual requirements and dietary provision. On-going diets will need careful fine-tuning to achieve optimal results.