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A Healthy Diet
The idea that diet may play a role in MS has been around for at lweast 40 years. One study in the 1980s showed that as any as two-thirds of people altered their diet after they found out they had MS. Now Dr Laurence Harbige and Dr Lorna Layward look at the facts.
There are a myriad of diets around for MS; some sensible, some bizarre and some downright dangerous. The reasons why people change their diet are many and complex. However the following are common motivations; firstly it is one way that people can take some control over the disease in the absence of other effective treaments and secondly the idea that diet may in some way be responsible for MS. While there is no convincing evidence that diet is responsible for MS, this idea may be attractive as it can provide an easy and tangible explanation to what is really a very complex and confusing disease. Just about every component of our diet has been put forward at some stage as being involved in MS. For most dietary ingredients, there is no objective, scientific evidence that they play any role in MS.
This article will concentrate on only one dietary component - fat - which has been implicated in MS for many years from the immune system attacking and destroying myelin as it would an invading micro-organism. It is not clear why the immune system turns on its own tissue, but ways to dampen down this harmful immune response are being developed and used as treatments for MS. There is scientific evidence that PUFAs can have an effect on the immune system. Animals with an experimentally induced disease resembling MS (called experimental autoimmune encephalomyelitis - EAE for short) are often used by researchers to study the mechanisms of myelin damage and to evaluate new treatments. When these animals are fed certain n-6 PUFAs they have either reduced or absent symptoms.
'It makes sense to maintain good nutrition for a healthy immune response. PUFAs, mainly fish oils, have also been used to alleviate the symptoms of animal models of other autoimmune diseases such as systemic lupus erythematosus ISLE) and rheumatoid arthritis. Trials in people with both these conditions, as well as in Crohn's disease, have also shown that PUFA supplements in their diet can help reduce symptoms.
The fact that dietary lipids can prevent symptoms in experimental animal models of autoinumme disease has been known for some time. However, the mechanisms by which lipids control disease have been obscure. Researchers have been looking at how dietary lipids work in EAE and have found that molecules called eicosanoids, made from dietary lipids, can alter the levels of cytokines which in turn affect the body's immune response. The particular type and balance of PUFAs that are beneficial in the animal model of MS (EAE) are being determined and purified.
A clinical trial is to be undertaken shortly at St Thomas' Hospital in London to see whether certain purified lipids are of benefit when people with MS take them as a supplement to their normal diet. The researchers have recruited all the people they need and the results will be known in two years time.
Nutrients need another look
While a role for other nutrients such as minerals and vitamins in MS has been suggested, there is no consistent evidence as yet for this. Similarly, allergies to certain foods have not been proven to be relevant to MS, although some people with MS will also have allergies purely by chance. There is no evidence that diets that exclude foods such as milk products or gluten have any beneficial effect on MS and diets that exclude certain foods may he harmful to general health. However, recent research has revealed new roles for nutrients such as some vitamins and minerals in the immune system. An understanding of the mechanisms by which nutrients interact with the immune system is needed before any possible role in MS may emerge. Only then can clinical trials be designed and undertaken and recommendations eventually made, based on their results.
So what diet should I follow?
We know that the immune system is sensitive to changes in nutrition, particularly when people are ill and do not eat properly. Poor nutrition can lead to poor immune responses. Since infections can trigger relapses in some people with MS, it makes sense to maintain good nutrition to support a healthy immune response. The World Health Organisation (WHO) recommends that we increase our daily intake of a variety of fruits and vegetables. They also recommend that we reduce saturated fats such as animal fats (e.g. dairy products) and increase intake of fibre-rich foods and complex carbohydrates such as pasta. These recommendations are aimed primarily at reducing heart disease and certain cancers in the general population and not specifically for MS. Other expert committees from the WHO, along with the British Nutrition Foundation, have taken thew guidelines further and recommended an increase in our diets of PUFAs from green leafy vegetables, fatty fish (such as salmon and mackerel) and other seafoods. It is therefore prudent to adopt these guidelines in MS despite the fact that such dietary changes have not been proven to be clinically beneficial in people with MS. Many people with MS supplement their diet with PUFAs, which in general has no harmful side effects. However, it is advisable to speak to your GP before making any changes to your diet.
A fat lot of good
But what do we mean by fat and what evidence exists for a link between MS and dietary fat? Fats, lipids or oils in our diet are used by our bodies in a number of ways: for storing energy; as an essential part of the structure and function of cell membranes; and for the production of substances called eicosanoids, which have a variety of biological functions. Fats are made up of fatty acids which come in two main forms: Saturated fats - which are solid at room temperature, such as animal fats (for example, lard); and unsaturated fats - which are liquid at room temperature, such as vegetable oils (for example, sunflower oil).
Saturated fats, used mainly for the storage of energy, are usually the first things we think about cutting out when we want to lose weight. There is some evidence that saturated fat may be a factor in MS.
Is the incidence of MS related to fat?
The incidence of MS differs with geography. In general, it is more common in countries further away from the Equator. the reasons for this are likely to be due to a combination of factors which include genetics, nutrition and exposure to viruses (see MS Matters 16). However, not all studies have shown that the geographic variations in MS are related to latitude. Studies in Norway revealed that there was less incidence of MS in coastal regions than in rural, inland, farming areas.
There was a difference in diet between these two regions,with a higher consumption of animal fat inland. Studies such as this, as well as others showing that consumption of unsaturated fats seem to be related to a lower incidence of MS, alerted people to the idea that dietary fat may play some role in MS.
Why are unsaturated fats so important?
As unsaturated forms of fats are important for many of the biological functions which could play a role in MS, people with MS and scientists have turned their attention to these. Unsaturated fatty acids are fats with at least one double bond linking molecules together. If they have more than one double bond they are called polyunsaturated fatty acids (PUFAs). There are two main families of PUFAs, n-6 and n-3. N-6 PUFAs am mainly found in vegetables and vegetable oils such as sunflower, safflower and evening primrose. N-3 PUFAs are found in some vegetables such as broccoli and spinach as well as in fish and fish oils.
The parent molecules of the PUFA families cannot be made by our bodies and so have to be obtained from diet and they are termed "essential fatty acids". It is very difficult to become deficient in essential fatty acids and there is no evidence that people with MS have gross essential fatty acid deficiency. However; reduced levels of linoleic acid (an n-6 PUFA) have been seen in people with MS, but it is hard to know whether this is a fundamental problem in MS or a result of having the disease.
Dietary studies and results
Over the years more than 30 studies have been published in scientific journals looking at various dietary components around the world and seeing if anything has a positive or negative effect on MS.These sum of studies are notoriously difficult to interpret and not all the studies are in agreement with one another However, when all these studies are looked at as a whole, it seems that MS repeatedly occurs where diets are high in saturated fat and seems to be less common in areas where PUFAs are consumed.
This evidence, along with the lowered blood levels of linoleic acid, was the basis of three Controlled clinical trials in the 1970s to see, whether adding n-6 PUFAs (sunflower oil) to the diet was of benefit for people with MS. Two of the trials showed a beneficial effect of Iinoleic acid whereas the third did not. However, a re-analysis of the trials all together found that there was a beneficial effect in reducing the numbers and severity of relapses and a slowing of disease progression in people with fairly mild MS. Another controlled trial looked at n-3 PUFAs (fish oil) in MS but no difference was found between those who took fish oil and those who did not.
Many people with MS supplement their diet with oil of evening primrose, but to date there have been no controlled trials carried our to determine whether evening primrose oil is of benefit in MS. Some people have been following a diet where they reduced the intake of fats (the Swank diet) for many decades. When these people were studied, it seemed that this diet had a beneficial long-term effect on their MS. However, this type of study must he treated with scepticism - by its very nature it is not controlled and less weight should be given to it compared to controlled trials.
What is the significance of polyunsaturated fats?
PUFAs have many different functions in our bodies beyond that of purely providing energy, some of which could have a bearing on MS. Because PUFAs are important for the structure and function of cell membranes they could be important in the make-up of myelin - which is made from the cell membrane of oligodendrocytes (see MS Matters 12 for further information on how myeIin is made).
This could result in faulty myelin, or leave it particularly susceptible to attack. Although there is experimental evidence that this can occur in animals, there is no firm evidence for this in people with MS.
Source - MS Insight March/April 1998 Supplement no 15. Reproduced with permission.