Epilepsy is a disorder where recurrent seizures (fits) are caused by abnormal electrical discharges from the brain. Most seizures can be controlled by one or more antiepileptic medicines but seizures may not be helped by these medicines after a while (called drug-resistant epilepsy). For people who have drug-resistant epilepsy a special diet (called a ketogenic diet) may be considered. Ketogenic diets are high in fat and low in carbohydrate.
This review aimed to investigate the effect of a ketogenic diet on seizure control, cognition (e.g., learning, concentration and academic performance in children; learning, concentration and memory in adults) and behaviour. We also investigated the side effects of the diet and the number of participants who dropped out of the studies and the reasons for this.
This evidence is current to March 2015.
We searched medical databases for randomised controlled trials (clinical studies where people are randomly put into one of two or more treatment groups) of adults or children with epilepsy where a ketogenic diet was compared with other treatments. We found seven randomised controlled trials, with 427 participants. The trials were between three and six months long.
The short-term side effects of ketogenic diets included diarrhoea, constipation and vomiting. In the long term, heart heath could be affected.
All studies reported participants dropping out, due to lack of improvement in seizures and poor tolerance of the diet.
No studies reported upon the effect of ketogenic diets on cognition and behaviour.
Recently, other, more agreeable, ketogenic diets, such as the modified Atkins ketogenic diet, found similar effects on seizure control as those more restrictive ketogenic diets. However, more research is required.
Quality of the evidence
The studies included in this review were limited by small numbers of participants and they only included children; therefore, the quality of the evidence was low.
There is little research at present into the use of these diets in adults, therefore, more research is required in this area.
The randomised controlled trials discussed in this review show promising results for the use of KDs in epilepsy. However, the limited number of studies, small sample sizes and a sole paediatric population resulted in a poor overall quality of evidence.
There were adverse effects within all of the studies and for all KD variations, such as short-term gastrointestinal-related disturbances, to longer-term cardiovascular complications. Attrition rates remained a problem with all KDs and across all studies, reasons for this being lack of observed efficacy and dietary tolerance.
There was a lack of evidence to support the clinical use of KD in adults with epilepsy, therefore, further research would be of benefit.
Other more palatable but related diets, such as the MAD ketogenic diet, may have a similar effect on seizure control as classical KD but this assumption requires more investigation. For people who have medically intractable epilepsy or people who are not suitable for surgical intervention, a KD remains a valid option; however, further research is required.
The ketogenic diet (KD), being high in fat and low in carbohydrates, has been suggested to reduce seizure frequency. It is currently used mainly for children who continue to have seizures despite treatment with antiepileptic drugs. Recently, there has been interest in less restrictive KDs including the modified Atkins diet (MAD) and the use of these diets has extended into adult practice.
To review the evidence for efficacy and tolerability from randomised controlled trials regarding the effects of KD and similar diets.
We searched the Cochrane Epilepsy Group's Specialized Register (30 March 2015), the Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies Online (CRSO, 30 March 2015), MEDLINE (Ovid, 30 March 2015), ClinicalTrials.gov (30 March 2015) and the WHO International Clinical Trials Registry Platform (ICTRP, 30 March 2015). We imposed no language restrictions. We checked the reference lists of retrieved studies for additional reports of relevant studies.
Studies of KDs and similar diets for people with epilepsy.
Two review authors independently applied pre-defined criteria to extract data and assessed study quality.
We identified seven randomised controlled trials that generated eight publications.
All trials applied an intention-to-treat analysis with varied randomisation methods. The seven studies recruited 427 children and adolescents and no adults. We could not conduct a meta-analysis due to the heterogeneity of the studies.
Reported rates of seizure freedom reached as high as 55% in a 4 : 1 KD group after three months and reported rates of seizure reduction reached as high as 85% in a 4 : 1 KD group after three months.
One trial found no significant difference between the fasting-onset and gradual-onset KD for rates of seizure freedom and reported a greater rate of seizure reduction in the gradual-onset KD group.
Studies assessing the efficacy of the MAD reported seizure freedom rates of up to 10% and seizure reduction rates of up to 60%. One study compared the MAD to a 4 : 1 KD, but did not report rates of seizure freedom or seizure reduction.
Adverse effects were fairly consistent across different dietary interventions. The most commonly reported adverse effects were gastrointestinal syndromes. It was common that adverse effects were the reason for participants dropping out of trials. Other reasons for drop-out included lack of efficacy and non-acceptance of the diet.
Although there was some evidence for greater antiepileptic efficacy for a 4 : 1 KD over lower ratios, the 4 : 1 KD was consistently associated with more adverse effects.
No studies assessed the effect of dietary interventions on quality of life, or cognitive or behavioural functioning.