This diet is reported to give the most favourable results, but it is very restrictive and requires a large amount of dietetic involvement in terms of calculations, monitoring, patient support and motivation of the family to adhere to the diet [7]. The diet contains a ratio of 4g fat to each 1g protein and carbohydrate combined; in children under the age of 18 months a ratio of 3:1 may be used. Children on this diet are unlikely to achieve a normal height or weight velocity, although there will be a compensatory growth spurt when the diet is discontinued. The dietary energy content is 75 kcal/kg and the protein content is 1g/kg body weight.

Calculation of daily amounts
If the patient's weight is Wkg then:

Energy content (kcal) = 75 x W

4:1 ratio

Fat content (g) = 7.5 x W
Protein content (g) = W
Carbohydrate content (g) = 0.875 x W

3: I ratio

Fat content (g) = 7.25 * x W
Protein content (g) = W
Carbohydrate content (g) = 1.44* x W

* rounded to two decimal places

Table 2 Example of a calculation of a 4:1 classical ketogenic diet
for a patient of weight (W) 31.4kg

Construction of the diet

• When the quantity of protein, fat and carbohydrate has been calculated the totals are divided into three to give the amounts for each meal (see Table 2).

• Meals are calculated which provide the necessary proportions of protein, fat and carbohydrate.

• To provide variation in the diet other 'whole' meals can be calculated which contain the required amounts of nutrients and one whole meal can be exchanged for any other whole meal.10ml double cream or 10ml Calogen can be utilised instead of 5g fat within any whole meal if this is more palatable.

Table 3 - 6g protein and 10g carbohydrate exchanges for ketogenic diets

Table 4 - 15g fat and 100 kcalorie exchanges for ketogenic diets

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