A ketogenic diet that's high in fat and low in carbohydrate has been used to treat seizures in children for over 90 years. In June 2008 the Journal Lancet Neurology published the results of the first randomised control trial of the ketogenic diet, in which it showed efficacy in children between 2 and 16 years of age, who had failed to respond to two anti-epileptic drugs (AEDs). This provided the first definitive evidence that it was effective.

In the short-term the ketogenic diet can cause bowel disturbance, raise cholesterol and, in rare cases, lead to kidney stones. These effects are usually temporary, however, and the diet is generally regarded as safe in the long term. Yet up to now there has been no scientific evidence to support or dispute this.

Researchers at John Hopkins Children Centre (JHCC), in Baltimore, USA, have now completed the first follow-up study into the lasting effects of the ketogenic diet, once this treatment is stopped.

The study looked at 101 patients, 2-26 years of age, who had been treated with the ketogenic diet at JHCC for periods of 16 months to eight years, between 1993 and 2008. All had stopped the diet between eight months and 14 years before follow-up. In addition to examining their clinical records, the scientists gave each person a detailed interview, to find out any medical problems that they were experiencing. Random groups of people also underwent biochemical tests, to assess liver and kidney function or cholesterol levels.

The results were very encouraging. Almost 80 percent of participants remained either seizure-free or had their seizures reduced by half after stopping the ketogenic diet. In addition, most children did not deteriorate in seizure control, even if the treatment had finished many years earlier.

During the interviews, no one reported cardiovascular problems such as heart attacks, enlargement of the heart or abnormal plaque build-up in their arteries, and only one person said that they had developed high blood pressure following the diet.

Among the 26 patients who had their blood cholesterol tested, the average level found was 157mg/dl (less than 200 is considered normal), and only three of the 26 had abnormal levels. Most patients' cholesterol levels increase whilst following the diet, but doctors generally believe that levels return to normal when the diet is stopped. These results study provide clinical evidence to support this.

Two participants experienced kidney stones after stopping the diet, but the researchers state that this is the same rate as that found in the general population not treated with the ketogenic diet.

None of the 25 patients who had liver and kidney function tests had abnormal results.

Most people who were older than 18 at the time of the study were found to have a normal body mass index, 22 on average (25 and below is considered normal). In addition, most of them were within a few inches of their expected heights, based on their parents' heights.

Those participants who were 18 years and younger at the time of the study were below average for height and weight, but less so than when they were following the ketogenic diet.

These findings are encouraging, because they suggest that most children who are treated with the ketogenic diet will catch up with their peers in terms of height and weight once the diet has been discontinued.

Finally, one fear of parents is that the ketogenic diet will alter their child's food preferences. However in the current study, only 8 percent of those in the study said they continued to eat predominantly high-fat foods.

The researchers wisely encourage people to view these results with caution, because there may be some effects that won't present for decades. However, the evidence found by these scientists, especially in people who had discontinued the diet for more than 10 years, suggests that the ketogenic diet does not cause long-term harm.

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Professor Helen Cross, Chair of Trustees for Epilepsy Research UK, is one of the world's leaders in paediatric epilepsy and the ketogenic diet. Click here to see the presentation about the ketogenic diet that she gave at our 2008 Evening Lecture.