Q:My understanding is that linoleic acid (and linolenic acid) are particularly important to health, provided certain co-factors are present in the diet.
This seems to contradict the article in WDDTY (Vol 5, No 4) on margarine which says that vegetable oils, rich in linoleic acid, were "potent promoters" of tumour growth.
There must be plenty of readers like myself who are confused by the apparent contradictions. Could you possibly shed some light on this issue and tell me whether margarines which have no hydrogenated oils are dangerous. My children and I are allergic to dairy products so I need to know the healthiest alternative to butter. Deborah Fox, Oxon.........
A:A great deal of confusion still reins about essential fatty acids (EFAs). An essential nutrient is one that must come from the diet, because the body cannot manufacture it. In order to metabolize fatty acids certain co-nutrients must be present these are B6, A, C and E and the minerals magnesium, zinc, copper and selenium. But this is not enough.
There are two main families of EFAs omega-6 (to which linoleic acid and arachidonic acid belong) and omega-3 (of which alpha linolenic acid is the most important). While it is true that, under optimum conditions, provided all the necessary co-nutrients are present, the body can manufacture alpha linolenic acid, our modern diets are far from perfect and it is thought in any case that the body does not manufacture it in adequate amounts. Thus in practical terms it is an essential fatty acid.
All EFAs are unsaturated which is to say they are liquid at room temperature and tend to go off quickly. This is why in modern food manufacture they are hydrogenated or partially hydrogenated to make them more solid (as in the case of margarines and spreads) and give them a longer shelf life. Hydrogenation is linked with heart and circulatory problems.
But the factor which plays the most crucial role in the development of many degenerative diseases such as breast and colon cancer is not hydrogenation but the ratio of omega-3 to omega-6.
The best ratio of omega-3 to omega-6 is one to one (Prev Med, 1987; 16:493-500). In the western diet the ratio is around one to 20.
Because of the popularity of using vegetable oils in cooking, salad dressings, margarines and spreads, most of us get plenty of omega-6 oils safflower, sunflower and corn oils are rich in omega-6 EFAs.
But only one vegetable oil is really rich in omega-3s food grade flaxseed oil (also known as linseed oil), which contains 60 per cent omega-3 and 20 per cent omega-6 (soybean, walnut and wheat germ oil may also contain useful amounts of omega-3, if their source plants were grown in a cold climate and if they are fresh, cold pressed and not hydrogenated). Other important sources of omega-3s are cod liver oil and fresh, oily, cold water fish such as salmon, tuna, mackerel, herring and sardines. The key word here is fresh since canning and deep frying destroys EFAs. Linseed oil has been shown to raise the body's level of HDL the 'good' cholesterol to a greater degree than soya or fish oil (Br J Cancer, 1990; 62:897-902).
Both omega-6 and omega-3 EFAs can also be found in dried beans such as kidney, navy and soybeans.
Recent evidence suggests that chemicals derived from arachidonic acid, a member of the omega-6 family, can produce a variety of metabolites that can initiate and promote the formation and spread of tumours, cell proliferation, tissue invasiveness and suppression of the immune system (see Ross Pelton and Lee Overholser, Alternatives in Cancer Therapy, Fireside Books, 1994).
The imbalance in EFAs is thought to be significant because these nutrients are the precursors for prostaglandin production in the body. Prostaglandins are a very important group of hormone like chemicals that regulate every major bodily function blood pressure, digestion, body temperature, fluid retention, blood cell stickiness, and the functioning of the reproductive vascular and immune systems to name a few. Over 50 different prostaglandins have been identified and scientists speculate that hundreds more will eventually be found.
Prostaglandins can have both a positive and negative effect on health. For example, they can both thin the blood and cause clotting. Too much platelet stickiness produces blood clots and can cause stroke and heart attacks but, if you cut yourself, you want to have some of that stickiness to form a scab so that you don't bleed to death. In a healthy system the functions of prostaglandins balance each other out.
There is an increasing amount of evidence to show that raising omega-3 fatty levels acts as a preventative especially for cancer. Fish oil has been shown to slow the progress of pancreatic and other cancers (J Natl Cancer Inst, 1985; 75:959-62) and can prevent breast cancer (Nutri and Cancer, 1989; 12:61-68). Animal experiments have shown that mice given a one to one ratio of omega-3 to omega-6 developed the least number of tumours (Cancer, 1990; 66:2350-56).
If you are avoiding hydrogenated oils in margarine and processed foods, you have taken the first step towards protecting your heart. The next step to ensure the rest of your body is healthy is to balance out the omega-6 intake with foods rich in omega-3 and that means fresh, unprocessed food like those listed above. Using olive oil can minimize omega-6 overkill.
If you are taking supplements, the oils of cold water fish may be preferable as supplements; not only do they supply the equivalent omega-3 fatty acids, eicosapentaenoic (EPA) and docosahexaenoic (DHA), but these substances are structurally closer to prostaglandins and past the biggest biochemical hurdle for their conversion. But even here there is disagreement since some experts believe that essential fatty acids in the form of EPA and DHA are so unstable that in supplement form they are unlikely to deliver the hoped for results (Udo Erasmus, Fats That Heal, Fats That Kill, Alive Books, Burnaby 1994).