Q:I have Dr Leo Galland's fascinating book Allergy Prevention for Kids in which he recommends linoleic acid (and linolenic acid) as particularly important to health, provided certain key co-factors are also present in the diet.
This seems to contradict the article (in WDDTY vol 5 no 4 ) on margarine which says that Professor Raymond Kearney of Sydney University stated in 1987 that vegetable oils, rich in linoleic acid, were "potent promoters" of tumour growth. You also quoted two studies from 1991 confirming that linoleic acid increases the likelihood of developing breast cancer.
There must be many other readers, like myself, who feel confused by these apparent contradictions. Could you possibly ask Dr Galland to give a response to this? Also can you explain whether a margarine such as Vitaquel, which has no hydrogenated vegetable oils, is also dangerous? My children and I are allergic to dairy products so I need to know the healthiest alternative to butter. D F, Oxon.
A:Lately, everybody is getting in on the butter vs margarine debate without shedding much light on the subject. After decades of government exhortation to consume more margarine to prevent heart attacks, most consumers are understandably left shaken by the recent revelations about the dangers of margarine.
The problem is not so much polyunsaturated oils per se; soy and safflower oils, after all, are rich in omega-6 fatty acids, which are essential to human health. The problem begins when they are heated, processed or otherwise tampered with.
According to our panelist Leo Galland, these oils present problems when they are overly refined. "Most commercial oils are extracted with extra heat added to enhance the extraction process," he writes. "This can create high temperatures, which damage the EFAs." Most refined oils are then further refined with solvents, using hexane-petrol to produce a lighter colour, taste and clarity, and even bleached, which removes many of the EFAs, trace minerals and vitamins, including antioxidants. Although all extraction processes generate heat to some degree, damaging some EFAs, those with the most nutrients left in are unrefined and coldpressed.
The second problem with polyunsaturates occurs when they are heated, particularly in a frying pan. These fatty acids can be easily damaged by heat. The oxidation caused by these heat-damaged oils creates free radicals in the body, damaging cell membranes and dramatically increasing your need for vitamins and minerals. This process has been implicated in cancer, hardening of the arteries and other degenerative diseases.
But the biggest threat to human health appears to be the manufacturing process of hydrogenation (or partial hydrogenation), done to prolong the shelf life of products. This is performed by heating up the oil to a high temperature and sending hydrogen through it. Dr George V Mann, in a recent review article hypothesizing about the likely role of partially hydrogenated foods and disease (The Lancet, 21 May 1994), explained that hydrogenation began after 1912, so that polyunsaturated fats could compete with butter and lard. During hydrogenation, trans fatty acids are produced; these artificial unsaturated fatty acids have a different molecular structure to those found in the tissues of humans and other mammals. "The amounts of TFA in commercial products vary from
5 per cent to as much as 75 per cent in the total fat," writes Dr Mann, particularly as neither America nor Britain requires that manufacturers state the amount of hydrogenated fat, only its presence. These substances can have a "disastrous" effect on your body's ability to use EFAs, says Dr Galland. They are even worse when heated, turning into something akin to the polymers in plastic.
Dr Mann argues that lipoprotein receptors in cells are impaired by TFAs. Since the body cannot process cholesterol-bearing low-density lipoproteins, the cells crank up their rate of synthesizing cholesterol, eventually leading to high levels in the blood. The amount of TFAs deposited in the body fat tissues reflects dietary intake. One study in Wales showed a strong association between TFA content in body fat and death from cardiovascular disease (Br J Preven Soc Med, 1975; 29: 82-90). In other studies, says Mann, blood cholesterol quickly increased in people fed TFAs (J Lipid Res 1992; 33: 399-410). He notes that coronary heart disease is high in northern European countries, where consumption of TFA is high, and low in the Mediterranean countries where the main dietary fat is olive oil and TFA intake is low.
There may also be another issue here. In his own studies of the African Maasai, young men consistently had low cholesterol concentrations, even though their diets were high in saturated fats, mainly from milk and beef. Dr Mann concluded that the Maasai, who got about 4-7g TFAs from cow milk, were below the threshold of where impairment of fat metabolism occurs. In America, the average daily intake of TFA is 12-20g daily. Or the story could be more complicated. Maasai could be protected because they are eating whole foods albeit containing saturated fats and not the adulterated ones consumed by most people in the West.
The bottom line is that researchers are only beginning to get to grips with the dangers of trans fatty acids. Until we are enlightened further, Dr Galland and others advise that you follow a number of basic principles. Cook with small amounts of olive oil. Although it contains non-essential fatty acids, it doesn't break down during storage or cooking to create substances that harm EFAs in your body. It also has been demonstrated in numerous studies to lower blood cholesterol and risk of heart disease.
As much as possible, eat whole foods and eschew anything that has been hydrogenated, processed or in any way interfered with. This would include most processed baked goods, canned sauces, commercial peanut butter, candy, "cheese" foods, crisps and corn chips. Small amounts of
margarine like Vitaquel, which are not hydrogenerated, may be okay as long as you don't cook with it.
Finally, look to getting your EFAs from oils that are not used in heating. This includes beans (soy, kidney and haricot beans, freshly soaked and cooked), salad oils loke safflower and sunflower oil, fatty fish, walnuts and linseed. Or take supplements like linseed oil (not heated), fish oils for omega-3 fatty acids and either evening primrose oil or blackcurrent seed oil for omega-6 EFAs.