Classical Diet The Classical Diet is based on a ratio of fat to protein and carbohydrate. Most of the fat on the diet comes from butter, cream, oil and other naturally fatty foods. Each meal has the same balance of fat, protein and carbohydrate and each part needs to be carefully weighed to the nearest gram. The diet is particularly useful for young children and tube-fed children. A normal diet should contain around 50% carbohydrate, 35% fat and 15% protein but the classical diet contains up to 90% fat, 6% protein and 4% carbohydrate.