An introduction to the ketogenic diet  




The ketogenic diet is a high fat diet which appears to benefit some people with epilepsy, particularly children. It is not a magic cure and is just one alternative to the various anti-epileptic drugs. The ketogenic diet may offer the advantages of more benign side effects and reduced impact on the mental development of children.

The ketogenic diet is often regarded as a difficult regime; however, with some care and a basic understanding of what the diet aims to achieve, it can be reduced to a readily manageable routine. The basic aim is to switch the primary fuel used by the body from carbohydrates (like bread and sugar) to fats; this is done by increasing the intake of fats and greatly reducing the intake of carbohydrates. The difficulty is that the level of carbohydrates must be very low, and the temptation of a single sweet can upset the diet for a small child.

A typical meal might include fish and green vegetables with a mayonnaise sauce followed by fresh fruit with lashings of cream, or bacon and eggs followed by coffee and yet more cream - so the diet is not as bad as you might have feared. There are a number of variants of the diet; in the US, a very high ratio of fats to carbohydrates is maintained, together with a low total calorie and fluid intake; in the UK it has been usual to adopt a more relaxed regime, supplemented by MCT oil (an extract from coconuts).

The reason why the ketogenic diet should reduce the level of fits is not understood; indeed many aspects of the ketogenic diet are less science and rather more black magic, and there is a need for much more research into the subject.

But isn't fat bad for you? . . .

Fats have had a bad press on the dietary front for many years. Diets (to reduce weight, that is) are mostly based on a low fat content. . . many "healthy" foods are advertised with a low fat content. . . cholesterol "kills". . .

The reality is a whole lot more complex. What makes people fat is not fats, but too many calories. Fats have an important role to play in nutritional health. Even cholesterol is not as bad as people believe. The role of fats and their dietary importance is discussed fully in the section   Understanding the ketogenic diet  . For the moment, be reassured, the high fat content of the ketogenic diet is not harmful, even if it may be somewhat indigestible.

Historical perspective

The ketogenic diet is not a new treatment. There is even a reference to fasting as a cure for fits in the Bible. Other early attempts at a diet for epilepsy include salt restriction, protein restriction, acid-ash diets and dehydration.

The first scientific study on fasting for the treatment of epilepsy was done in France in 1910; this reported that fits stopped during absolute fasting. Later, other investigators observed cessation of fits and improvement in mental activity during starvation. These results prompted the use of a high fat - low carbohydrate diet in 1921 by Wilder at the Mayo Clinic, although he was trying to prolong the state of ketosis in diabetics. At about the same time, Howland and Gamble at the Johns Hopkins Department of Pediatrics, observed that "prayer and a water diet which involved starvation for three to four weeks" reduced the fits of the nephew of a professor of paediatrics. They decided to investigate the diet because they thought prayer alone was ineffective. Others like Lennox and Cobb at Harvard University also started to study the ketogenic diet.

By 1924, Peterman at the Mayo Clinic was using the diet largely in its present form, and the treatment became widely used in the 1930s. After the second world war, Livingston at Johns Hopkins studied almost one thousand patients using the ketogenic diet and reported excellent fit control. But subsequently, interest in the ketogenic diet declined as the newer anti-epileptic drugs were introduced.

At the end of the 1980's, interest in the diet was revived by John Freeman at Johns Hopkins, who reported a study in 1992 showing that the diet produced complete fit control in 30% of children with previously uncontrollable fits, and that an additional 38% showed marked improvement .

One of the children treated successfully by the Johns Hopkins team was Charlie Abrahams. In gratitude, his parents have created the Charlie Foundation, which has given widespread publicity to the diet, in part by making available a free video tape.

How does the ketogenic diet work?

The food we eat provides the fuel used by our bodies for everyday activities; it also provides the raw materials to manufacture and replenish the body itself. Unlike the motor car, which can only run on petrol, our bodies are designed to use a variety of fuels, as they are available.

The three main types of fuel for the body are carbohydrates, fats and protein. Carbohydrates are things like sugars, starch and flour which come mostly from plants. Fats come in two broad types - saturated fats, like butter, which mostly come from animals and unsaturated fats, like corn oil, which mostly come from plants. Finally, protein comes mainly from animals and is represented by meat and fish. The preceding is a broad generalisation and there are many variations - nuts, for example, often contain more than 50% fat.

All the fuels work in the same way. They undergo a chemical reaction with the oxygen we breathe, and this releases energy for use in the body and creates waste products including carbon dioxide and water. This is just the same reaction that happens with petrol in a car, or when we have a fire and burn coal or wood. The body is far more efficient, and the food metabolises (oxidises) at body temperatures, whereas the petrol in a car or the wood for a fire will only burn (oxidise) when they are raised to a very high temperature.

The three fuels are used by the body in different ways. The fuel of preference is carbohydrate, and the body will use up its store of carbohydrate before using other fuels. Carbohydrates are quick acting - athletes take glucose tablets to provide energy - typically carbohydrates will be used within a few hours of eating, which is why we eat so frequently. By contrast, the primary role of fats is to store energy - animals fatten up to prepare for the rigor of winter. The body normally tries to store the fats we eat, but will use them as fuel if there is not enough available from carbohydrates; first it will use the fats in the food, and if these are insufficient it will start to deplete the fat storage in our body tissue. Fats metabolise more slowly and typically it will take a day or so for the fat content of food to be used. That is why we feel full after a fatty meal, and why it really is a good thing to line to stomach with milk before drinking - the fat slows down the metabolism of the alcohol. The third fuel, protein, is primarily used to build and replenish body materials, any excess being metabolised as fuel.

In a typical western diet, the proportion (by weight) of the three fuels that is used will be about 10%+/-5% protein, 15%+/-5% fats and 75%+/-10% carbohydrates; if there is any excess it will be wasted by the body, in order to maintain the correct input, so that it is not necessary to be all that precise about the food we eat. By contrast, in the ketogenic diet, the proportion of fats is raised significantly and the proportion of carbohydrate is greatly reduced. It is also necessary to control the total intake of food, since if the body is given excess, it will discard the fats preferentially, in an attempt to get back to its preferred balance of fuels; by restricting the total fuel intake, the body is forced to use fats in place of carbohydrates.

In normal operation, the human body converts the various fuels into glucose, which is the preferred fuel for use in individual cells and ketones. If there is insufficient fuel to meet its needs the body uses its stored resources. First the body burns any glucose stored as glycogen, and then it burns body fat; it also burns protein from muscle tissue specifically to provide glucose for use in the brain. As fasting continues, the pattern changes again, and the brain starts to use ketones manufactured from body fat instead of the glucose manufactured from muscle tissue as its source of fuel. It is this change which appears central to the success of the ketogenic diet. When the change occurs the body is said to be in ketosis and some of the ketones are excreted and can be detected in the urine. Ketones are just another class of organic chemicals; the simplest and most widely known is acetone which has a very recognisable smell and is used as a solvent in dry cleaning and glues.

The ketogenic diet mimics the effect of fasting by denying the body the carbohydrate it requires to metabolise normally. It may take as long as a week for the body to switch into ketosis after starting the diet. Ketosis is readily recognised, because the ketones that are excreted in the urine can be detected by a simple test; ketosis can also be recognised by the characteristic acetone smell in the breath or the urine.

It appears that the prophylactic properties of the ketogenic diet build up with time and it may be several weeks before the full effects of ketosis are achieved. There is often a similar pattern when the ketogenic diet is stopped, the effects of the diet persisting for several weeks.

While ketosis may help reduce fits, it has other less desirable effects. Ketosis will increase the acidity of the blood, and can reduce appetite; there may also be some continued loss of protein from muscle tissue.

So, the reason why the ketogenic diet works is that it induces a state of ketosis - but why that should have a beneficial effect on fits is not understood.

Who can use the diet?

The diet has mostly been used for children aged between one and six years. The reasons for this seem to be practical - the diet is seen to be difficult to implement with smaller children, and difficult to maintain with older children, given the temptations of more interesting foods. However, this may be changing; there has been a trend towards using the diet on even younger children, while its use is also being considered for older children and for adults.

Studies on the use of the diet report success rates comparable with most forms of drug treatment: about 30% of patients show a marked improvement (reduction of fits by 50% or more), 40% show a small or no significant improvement and 30% show an adverse effect. These results are surprisingly good given two factors:

There are no indications that the diet is more effective for some types of fits than others, although it may be more easy to administer when fits are more frequent.

Comments from some satisfied customers

Of course, these comments are anecdotal, and there are many others who have not benefited from the diet in the same way.

So. . . what is this diet?

Unlike most diets, the ketogenic diet is not very prescriptive about the actual foods that are used; it is solely concerned with maintaining a particular ratio of fat to carbohydrate and protein.

There are a number of variant diets. The classical 4 to 1 diet contains four times as much fat as carbohydrate plus protein. (For comparison, in a normal diet there is less than half as much fat as carbohydrate plus protein.) As well as maintaining this ratio, the total energy intake is restricted to about three quarters of the normal, and liquid intake may also be controlled. It should be noted that the 4 to 1 ratio is the ratio by weight.  Because a gram of fat produces more than twice the number of calories produced by a gram of carbohydrate or protein, this is a 9 to 1 ratio by calories, so that 90% of the energy intake of the body is coming from fat.

The diet is normally introduced by a period of hospitalisation. Prior to going to hospital, the victim is starved for 12 hours. On entry to hospital, a reference EEG will be taken, and the child continues to fast. By the next day, ketosis should be achieved, and the diet will start at one third of the recommended calorie (fuel) intake. On day four the calorie intake will be increased to two thirds the recommended level, and on day five the full intake will be achieved. Providing there are no complications the child will then be discharged. Meanwhile during the period of hospitalisation a suitable diet will have been designed and the parents will have been briefed on its operation.

In variants of the diet, the ratio of fat to carbohydrate plus protein may be reduced below 4 to 1, to 3.5 to 1 or 3 to 1, or it may be increased to as much as 5 to 1. Typically the lower ratios are used with younger children. Also, once the diet is in operation successfully, the ratio may be reduced over time as far as possible, providing the beneficial results continue.

A much more significant variant is the MCT oil diet. MCT stand for medium chain triglycerides, which are a particular type of saturated fat found in coconut oil. MCT oil is one of the wonder ingredients of the nineties, being used by athletes to improve their performance. MCT oil is special because although it is a fat, it metabolises quickly, like carbohydrate.  In the typical MCT diet, the proportions will be 35% fat, 35% MCT oil, 20% carbohydrate and 10% protein (a 2.3:1 ratio). Also, the total calorie intake is set at the normal level, rather than three quarters of normal, so the MCT diet is far less rigorous than the classical diet. There does not seem to be any very clear rationale for these variations from the classical diet, except the pragmatic one that it is claimed they work, although this claim is hotly disputed.

return to   The ketogenic diet


(checked: 13 November 2002)
(update 2.5: 31 February 2003)
(issue 2: 20 February 2000)