The ketogenic diet, itself, is not prescriptive about fats, and largely regards all fats as equal, although the protocols from individual hospitals may make rather stronger recommendations about which fats to use.

There is, however, more general dietary information about fats, most of which should be directly applicable to the ketogenic diet. Indeed, because of the very high content of fat in the ketogenic diet, general dietary concerns about fats should be regarded very seriously.

Some more chemistry

Fats and oils are organic chemicals (ie contain carbon and hydrogen atoms) which are not soluble in water. This is an important factor for biochemistry. It means that fats cannot be directly transported through the blood stream, and that they can be used to make the skin for miniature bubbles in the body containing all sorts of chemical goodies – these bubbles are, of course, the various types of cells in the body.

The most relevant group of fats and oils is called the triglycerides. Each triglyceride consists of a short back bone connecting three chains of carbon atoms. A triglyceride can be represented schematically, using a C to represent each carbon atom, an H to represent each hydrogen atom and an O to represent each oxygen atom, and a – to represent a bond between each atom. Thus a typical triglyceride might be:

..H.. O H H H H H H H H H H H H H H
..|...N | | | | | | | | | | | | | |
H-C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H
..|.....| | | | | | | | | | | | | |
..|.....H H H H H H H H H H H H H H
..|
..|...O H H H H H H H H H H H H H H
..|...N | | | | | | | | | | | | | |
H-C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H
..|.....| | | | | | | | | | | | | |
..|.....H H H H H H H H H H H H H H
..|
..|...O.H H H H H H H H H H H H H H
..|...N | | | | | | | | | | | | | |
H-C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H
..|.....| | | | | | | | | | | | | |
..H.....H H H H H H H H H H H H H H

Although triglycerides are the normal form of fats and oils that are found in foods, within the body a triglyceride is usually broken down into its three separate chains, so the triglyceride above would give three molecules of the fatty acid:

... O H H H H H H H H H H H H H H
... N | | | | | | | | | | | | | |
H-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H
......| | | | | | | | | | | | | |
......H H H H H H H H H H H H H H

This is the myristate fatty acid, so called because it occurs in nuts. The formal chemical name is n-tetradecanoate (because the chain has 14 carbon atoms).

Note that the fats and oils that we use in cooking are triglycerides. During digestion, these are broken down by the enzyme lipase into their component fatty acid chains. Common parlance is not very pecise and often uses the terms fats, oils and fatty acids interchangeably. When you buy essential fatty acids at a health food store, what you actually buy is an unsaturated triglyceride oil; it is only when it is metabolised that it actually turns into fatty acids. Sorry if that is confusing.

There are three important things to remember about molecules:

• They are three dimensional.
• Most of their physical properties are determined by shape.
• They are flexible, and each of the links can bend and rotate.

Thus, the rigid two dimensional diagrams that I have given are somewhat misleading. A triglyceride is not so much like a fork with three prongs, but rather more like a piece of seaweed with three fronds waving in the sea.

Now we need another bit of chemistry. The fatty acid we have been looking at is a saturated fatty acid, which means that every carbon atom (except at the two ends) has two hydrogen atoms connected to it. There are also unsaturated fatty acids, in which a pair of hydrogen molecules are taken away, giving a "double bond" between a pair of carbon atoms:

... O H H H H H H H H H H ... H H
... N | | | | | | | | | | ... | |
H-O-C-C-C-C-C-C-C-C-C-C-C-C=C-C-C-H
......| | | | | | | | | | | | | |
......H H H H H H H H H H H H H H

This is an omega 3 fatty acid – omega 3 tetradecanoate. All that the words omega 3 do is to tell us the position in the chain of carbon atoms of the double bond. The left hand end of the molecule is called the alpha end, the right hand end is called the omega end. So, omega 3 means there is a double bond between the third and fourth carbon atoms from the omega end. It is called an unsaturated fatty acid, because it is chemically possible to remove the double bond by replacing it with two hydrogen atoms, getting back to the saturated acid (ie with the maximum number of hydrogen atoms.

We now need to know something else. Unlike the single bond, which is like a flexible hinge, the double bond is rigid. This means that there is a second form of this fatty acid, with a hydrogen atom on either side of the double bond:

... O H H H H H H H H H H H ..H H
... N | | | | | | | | | | | ..| |
H-O-C-C-C-C-C-C-C-C-C-C-C-C=C-C-C-H
......| | | | | | | | | | . | | |
......H H H H H H H H H H . H H H

The first version of the fatty acid, with both hydrogens on the same side is called the cis- form and the second version with a hydrogen on either side is called the trans- form.

While the general chemical properties of the cis- and trans- forms are the same, their physical properties are different. When the two hydrogen atoms are on the same side (cis-) the molecule is asymmetric, and a kink is formed in the chain of carbon atoms, because the missing hydrogen atoms create a gap where the molecule can bend. Where the two hydrogens are on different sides, the molecule is symmetrical, and the carbon chain remains straight.

One of the features of biochemistry is that not all the possible variants occur naturally. Double bonds only occur in nature in the omega 3, omega 6 and omega 9 positions (and occasionally the omega 7 position). It is also possible to have unsaturated fatty acids with more than one double bond. They are even more kinky, and are the poly-unsaturated acids. Another quirk of nature is that only the cis- forms are found naturally, never the trans- forms of unsaturated fats.

You might wonder what all this has to do with nutrition and the ketogenic diet. the answer is everything.

Butter and margarine

We all know what butter is. It is a soft spreadable food, which softens further, and eventually melts as it is heated. Butter is a saturated triglyceride. What I did not tell you before is that the typical triglyceride does not have three identical chains, but rather each chain is a different fatty acid. Butter is actually a complex mixture of different saturated triglycerides. This is why butter does not melt suddenly, but gradually softens as it is heated. The temperature at which a particular triglyceride melts depends on the length of the fatty acid chain. The longer the chain, the higher the melting temperature. The gradual softening of butter as it is heated is caused by the melting of the different triglycerides at different temperatures.

Something else affects the melting point of a fat - the shape of the molecule. The more irregular the shape, the higher the melting point. Obvious, really - the regular saturated triglycerides are rather like sticks and pack together readily to form a solid. The kinky unsaturated triglycerides are like twigs, they will not conveniently pack together into a solid and therefore tend to melt at a lower temperature.

So saturated triglycerides are usually solid, ie fats, whereas unsaturated triglycerides are usually liquid – ie oils. It is also the case that most saturated fats come from animal produce, while most unsaturated oils come from vegetable produce.

Now we get to hydrogenation. We like to eat butter. It is an animal fat, and expensive. Vegetable oils, by contrast are much cheaper. Wouldn’t it be nice to make a spreadable fat out of cheap vegetable oil. Chemists can do this by heating the oil to a high temperature in an atmosphere of hydrogen using a metal catalyst. This breaks the carbon double bond and replaces the bond with two hydrogen atoms - hydrogenation. Sounds great. Unfortunately, the result of hydrogenation is a very hard fat, not at all like butter. But wait a moment, suppose we did not hydrogenate the oil for so long? Success! we get a soft spreadable fat, whose properties we can control, depending on the degree of hydrogenation. This is margarine.

Unfortunately, margarine is a soup of all sorts of triglycerides; it contains both saturated and unsaturated fats. More seriously, the process of hydrogenation tends to convert the cis- fatty acids to trans- fatty acids. Now, why should that matter?

The answer is that biochemistry is selective. As I have already said, not all the possible variants of organic chemicals occur in nature. Biochemical systems consist preferentially of certain types of molecules:

• The number of carbon atoms in a triglyceride chain is always even.
• Double bonds in triglycerides usually only occur at omega 3, omega 6 and omega 9 positions.
• Unsaturated fatty acids occur in the cis- form rather than the trans- form of triglycerides, and it is only the cis- form that the body requires.

Hydrogenation is a very crude chemical process and the resulting triglyceride soup breaks all these rules; in particular hydrogenated fats contain significant proportions of trans- fatty acids. The figures are approximately:

• Margarine 10% - 50% trans- fatty acids.
• Vegetable oils 10% -40%
• Salad oils 5 –10%

Now we come to the contentious bit. What is not so clear is what effect these trans- fatty acids have on the body. Some biochemists believe that they have no effect on the body, some believe that in large quantities they can make some of the biochemical systems less effective, and some believe that they can be seriously harmful. You can take your choice.

There is another thing about margarine. I said that the process of hydrogenation used a metal catalyst (that is, a chemical which facilitates a chemical reaction without itself being used up). The metal catalyst is a combination of platinum and aluminium, and margarine is contaminated, particularly with aluminium. And aluminium is one of the possible causative agents for Alzheimer’s disease.

So there is it. Margarine and other hydrogenated fats contain trans- fatty acids and aluminium. Both are substances which may be significantly harmful to our metabolism. Under these circumstances, the prudent person would not use margarine or other hydrogenated fats whenever these could be avoided.

The ketogenic diet itself has a very high fat content, so the concern about hydrogenated fats is even more important. My recommendation would be to play safe, and do not use hydrogenated fats.

Fat as a fuel

Metabolically, fats have two main roles. The primary role is to act as a source and as a store for energy in the body. The energy comes from the body burning, that is oxidising, the fat. Unlike a car burning petrol, or a fire burning wood, this is a very efficient process which is done at body temperature, using a complicated chemical process which oxides the two carbon atoms at the omega end of a fatty acid chain. Oxidising means that oxygen from the air we breathe is combined with the two carbon and four hydrogen atoms at the end of the chain, to create two molecules of carbon dioxide (CO₂) and two atoms of water (H₂O). The fifth hydrogen atom is replaced at the end of the fatty acid chain, leaving a fatty acid that is now shorter by two carbon atoms. This process can be carried out repeatedly until the fatty acid chain is completely used up.

I said the chemical process for metabolising fats was complicated. It is, and it involves a number of other organic chemicals to make it work. In particular, it involves carnitine and various co-enzymes, including co-enzyme Q10.

Because fats consist almost solely of simple chains of CH₂ links, fats are the ideal source or store for energy. This can be seen from the fact that they deliver about 9Kcal per gram, more than twice as much as carbohydrates or protein. Since the oxidation process operates on the end of the fatty acid chain, it does not matter how long the chain is, nor the sort of fat that is used – saturated, unsaturated, cis- or trans-, they all work as well. The only difference between fats is that there is a waste residue in each fat molecule (the glycerol head at the alpha end), so that the shorter molecules deliver slightly less energy per gram – which is why MCT oil has a lower energy value than average fats.

From this we can deduce a number of things relevant to the ketogenic diet. The first is that as a source of energy, it does not matter what sort of fat we eat – they are all broadly equivalent. We can also deduce that the availability of the organic chemicals which facilitate the oxidation of fats may be important to the operation of the ketogenic diet. In particular, because the body is metabolising far more fat than normal (by a factor of as much as three), it may be necessary to supplement these organic chemicals to ensure the oxidation process operates properly.

Other fats

The second role for fats is quite different. They are used as the source for the building blocks of the cell membrane. The building block is a phospholipid - which is a triglyceride in which one of the outside chains has been removed and replaced by a phosphate group (a simple organic chemical containing an atom of phosphorus).

......H.. O H H H H H H H H H H H H H H
......|.. N | | | | | | | | | | | | | |
....H-C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H
......|.....| | | | | | | | | | | | | |
......|.....H H H H H H H H H H H H H H
......|
......|...O H H H H H H H H H H H H H H
......|...N | | | | | | | | | | | | | |
....H-C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H
......|.....| | | | | | | | | | | | | |
......|.....H H H H H H H H H H H H H H
......|
..O...|
..N...|
R-P-O-C-H
..|...|
..O^-..H

Since phospholipids are the basic building blocks of cell membranes, they are present in all organic matter, particularly meat. They can also be readily created in the body from triglycerides, and this is the normal source.

The reason that phospholipids can be used as the building block for cell membranes is that they are very different in their behaviour in relation to water. Triglyceride fats are completely insoluble in water. Put some fat (oil) into water, and it remains in little globules. Put a phospholipid into water and it will rapidly spread out and form a thin skin over the surface of the water. The skin is very thin - it is exactly one molecule thick. This is because, unlike triglycerides, one end of the phospholipid (the alpha end) is attracted to water, while the other end (the omega end) is repelled. Thus, the skin consists of all the stick like phospholipid molecules upended, with their heads sticking to the surface of the water and their tails as far away as possible. The best analogy I can think of is tadpoles clustering in the water when the sun is shining, except that these are the other way up, with their heads on the surface of the water, and their tails sticking down into the water.

Now, just imagine taking a second skin of phospholipid molecules, and putting it back to back with the first, so that the omega end tails are together, and the phosphate alpha end heads are on the outside. What we get is a thin membrane, exactly two molecules thick, which can have water on either side, and through which the water cannot pass. Curl this membrane around on itself to create a hollow ball with the phospholipid skin as the shell, and we have exactly what nature wants, a little container (the cell) that can hold all sorts of chemical goodies (exactly what depending on the type of cell).

So, the second major role of fats is to create the cell membrane. It is here that the unsaturated fats have an important role to play. You will remember that the saturated fats are stick like, and pack together efficiently, whereas the cis- unsaturated fats have kinks, and do not pack together so well. This is key to the operation of the cell membrane. It is all very well to create a barrier between the outside and the inside of a cell, but this is no use if selected molecules cannot pass in and out through the membrane. This is achieved by making the membrane semi-permeable, using a mixture of saturated and unsaturated phospholipids, the kinked unsaturated phospholipids creating gaps in the membrane. This allows selected small molecules to pass through the membrane and also allows selected proteins to become embedded in the membrane which can act as controlling gateways allowing specific types of molecule to enter or exit the cell. Thus, essential fatty acids are required to create the right properties in the cell membrane for each different type of cell.

This is highly relevant to epilepsy, because the underlying problem in epilepsy is the avalanche firing of neurons in the brain. The neurons are, of course, a particular type of cell, which can communicate with other neurons. They do this by the synaptic junction, the point where two nerves cells touch (remember, a nerve cell is not a globule, it is something with a body (the soma) and a lot of tentacles which reach out to touch the soma of other neurons. All of the outer structure of a neuron is cell membrane, and the synaptic junction is the most critical area of cell membrane in the body, since it has to precisely control the chemical messengers that pass form one neuron to another to make up the signalling system which enables the brain to work. The synaptic membrane is the most complex and subtle membrane in the body. One possibility for the underlying mechanism of epilepsy is that the neuron synaptic membrane is defective in some way.

The quantities of essential fatty acids required in the human diet are not well established. This is true for most other things as well, including vitamins, but it is worse with essential fatty acids. The quantity is of the order of 1% of dietary intake - that is, it is rather more than 0.1% and less than 10%. So, quite small quantities of essential fatty acids are sufficient in a normal diet. If the quantity is not well known in a normal diet, you can be sure that it is even more uncertain for children, or for the ketogenic diet.

Thus, essential fatty acids are just that and play a very important role in the body, which is closely related to the problem of epilepsy, and it is very possible that the types of fat used in the ketogenic diet may have an important influence on its operation and success.

Are essential fatty acids always the good guys?

However, it is not quite that simple. There are two problems associated with essential fatty acids - trans- fatty acids and free radicals.

Essential fatty acids are fragile; if you buy them, they will come in a brown bottle inside a container, and there will be instructions to keep them in the refrigerator and away from light. That is because the double bond, which makes a fatty acid essential, is easily damaged, by stray rays of light or gentle heating. When the bond is damaged, the benefit of the molecule is destroyed and worse, it may become positively harmful, turning into a trans- fatty acid, or creating free radicals, or other undesirable organic fragments. The precise extent to which these things are harmful is a matter of debate, but it does seem desirable to avoid any risk. In the context of epilepsy and the ketogenic diet, the main thing to be concerned about seems to be avoiding trans- fatty acids.

There is a risk with essential fatty acids is that they may already contain trans- fatty acids. It is very easy for the cis- fatty acids to be damaged by the extraction processes, which usually involve heat and pressure, and so there is a likelihood that the bonds will be damaged. To quote from Efamol (which obviously has a commercial interest in the matter):

The secret of extraction is how to penetrate the seed without impairing the oil. Regrettably, traditional techniques, such as cold pressing, though effective with culinary oils, generate heat that may destroy irreplaceable ingredients. The process requires so much pressure that the resulting oil is often dirty and of poor quality. Chemical refining is usually used to clean up the oil, but it often causes more damage than it repairs and increases the degradation of the oil.

The extent to which trans- fatty acids are a problem is not reliably established. The fear is that they will poison various of the metabolic processes, being used by the body instead of the cis- fatty acids. In the case of the membrane, if a trans- fatty acid is used in place of a cis- fatty acid, because the trans- fatty acid is not kinked, it is much the same as using a saturated fatty acid, and the permeability of the membrane won’t be increased. It does seem that the body has some protective mechanisms to reject trans- fatty acids, but that these may be inadequate to cope with large quantities of trans- fatty acids. Also, these protective mechanisms may not apply to all the metabolic processes which use cis- fatty acids.

Free radicals are a very different issue. Both cis- and trans- fatty acids contain the oxygen double bond, which connects the oxygen atom to a carbon atom. Double bonds are under a lot of stress, and are very easily broken. If you have ever made models of chemical molecules, using little balls connected by springs, you will remember how difficult it is to put together a double bond, and how easily it breaks, because the two springs representing the double bond have to be bent round to fit between the carbon and oxygen atoms. It is just the same in the real molecule, the double bond, and the hydrogen bonds nearby are under stress, and are easily broken. Stray photons of light, for example, can break the bonds in the area of stress, causing the fatty acid to break up into a variety of fragments. This is a chain reaction, because it releases a free radical (containing an unpaired electron), which can go off and wreak the same havoc elsewhere. Damage of a single bond is not important - there are an awful lot of bonds in a bottle of oil; however, when one is damaged, the problem can propagate via free radicals to damage hundreds of thousands of other bonds. Free radicals are why essential fatty acids should be kept in brown bottles in the refrigerator, and is why fats go rancid.

Free radicals are thought by some to be the causative factor in degenerative diseases; their generation is promoted in the body by the presence of essential fatty acids with their highly stressed bonds. Again, however, the body has protective measures to deal with free radicals (the primary role of vitamin C), so the extent to which free radicals are a real problem is not established.

Thus. while essential fatty acids are essential, their use carries the risk of contamination by trans- fatty acids. They are also biologically active (generate free radicals) which is undesirable. As a result, it is necessary to think carefully about the use of essential fatty acids in the ketogenic diet.

Fats and the ketogenic diet

What does all this mean in the context of the ketogenic diet? The answer is complex and unsatisfactory. It is possible that the precise types of fat used in the diet are important, particularly because the synaptic membrane is at the centre of whatever goes wrong in epilepsy. But there is no information to guide us.

There is also the general dietary consideration, that the body must have an adequate supply of all the relevant nutrients. Our genes give us the constitution of a scavenger, capable of subsisting on a wide variety of diet. This means that, on the whole, we should be fairly tolerant to the details of diet, providing it does not deviate excessively from a broad variety of ordinary foods. The risk is less that we miss some essential nutrient and more that we ingest some man made organic chemical which does not occur naturally, and which interferes with our normal metabolism. In this respect, essential fatty acids are very much a two edged sword. Most essential fatty acids contain at least some trans- fatty acids, and if they are poorly prepared, or are not handled carefully, they may contain significant quantities of trans- fatty acids. Also, essential fatty acids will generate free radicals, which may be a possible cause of various degenerative diseases. Thus, while it is necessary to have sufficient essential fatty acids in our diet, excess quantities may be positively harmful - this risk is increased with the ketogenic diet, because the level of fat intake is so much higher.

A philosophy for the use of fat in the ketogenic diet

• Use natural foods and avoid as much processed food as possible, particularly foods that might contain hydrogenated fats.

• Use as varied a range of fats as possible, avoiding hydrogenated fats and being very careful when using essential fatty acids that these are not contaminated by trans- fatty acids.

• Remember that it is wrong to think of saturated fats as bad. They are at least as essential to the diet as unsaturated fats.

• When buying essential fatty acids, it is essential that they are prepared by a reputable supplier to ensure that they are pure and do not contain trans- fatty acids

• Do not use margarine.

• Avoid other hydrogenated oils like cooking oils and salad oils, and certainly do not cook with them.

• Do not use essential fatty acids for cooking (ie don't heat essential fatty acids).

• Do not use more essential fatty acids than you believe to be necessary - while the diet should include essential fatty acids, an excess may be positively harmful.

• Finally, it may be necessary to supplement the diet with special nutrients like lipase, carnitine and co-enzyme Q10 in order to facilitate the additional burden of fat processing imposed by the ketogenic diet.

continue to   Trans-fats
return to   Understanding the ketogenic diet

(checked: )
(update 2.2: 18 July 2002)
(issue 2: 26 January 1998)