The Ketogenic Diet (KD) is a medically managed and carefully calculated high-fat, low carbohydrate diet, designed to mimic a fasting state over a long period of time. It is available as a treatment option for children with difficult-to-control epilepsy and some neuro-metabolic disorders.
When on the Ketogenic Diet, a simulated ‘fasting state’ is achieved by forcing the body to burn fats to produce ketones rather than carbohydrates. When there is very little dietary carbohydrate, the liver converts fat into fatty acids and ketone bodies. The ketone bodies then pass into the brain, replacing glucose as the primary energy source. This elevated level of ketone bodies in the blood is referred to as ketosis.
Although the exact mechanism of action remains unclear, when ketone bodies become the main energy source for the brain, it is thought to mimic the biochemical response to starvation, 1 a practice used historically to control seizures.
Process for achieving ketosis
- Carbohydrate consumption is limited to deplete carbohydrate stores
- Fats are subsequently burnt without carbohydrates
- Mitochondrial beta oxidation transforms fatty acids into ketone bodies
- Ketone bodies (acetone, acetoacetate, and beta-hydroxybutyrate) accumulate in the blood, urine, and CSF
- This process affects seizure onset and propagation, and
- In many cases, leads to reduction/cessation of seizures
The classical Ketogenic Diet
Uses four grams of long chain fat to every one gram of carbohydrate and protein combined. This is described as the 4:1 ratio:
- 90% of total energy comes from long chain fats
- 5-7% of total energy comes from protein
- 3-5% of total energy comes from carbohydrate
Variations on the classical Ketogenic Diet
- Medium Chain Triglyceride Diet (uses medium chain triglycerides which produce higher ketones compared with long chain fatty acids and has the benefit of being absorbed faster. Products used = MCT oil, Liquigen, or Coconut Oil)
- Modified Atkins Diet (total fat required as energy source is 60-65% rather than 90% as per the Classical diet variant. No limit on calories or protein) 
- Low glycaemic Index Diet (attempts to achieve stable blood glucose levels) 2