The Facts About Fat - Can It Really Be Good For Us?
Various aspects of food and health are in the media all the time, but there is quite a bit of technical jargon which can be confusing. Most people will have heard of omega-3 fatty acids and have some idea that they are good for us. But what do they actually refer to and are they really good for us?
Approximately 95% of the fat in our diet is composed of molecules called triglycerides. Each molecule has a glycerol 'backbone' with three fatty acids attached. The glycerol never varies, but the fatty acids can vary considerably depending on the food source. Each fatty acid has a carbon chain which can be completely 'saturated' with hydrogens (saturated fatty acids) or partly saturated and having one double bond (monounsaturated) or two or more (polyunsaturated). There are two main classes of polyunsaturates - omega-3 and omega-6, the numbers relating to the position of the first double bond in the carbon chain.
On average, in the UK, our consumption of omega-6s, which help to lower blood cholesterol, has increased considerably in the last 20 or 30 years due partly to the widespread introduction and intake of polyunsaturated spreads and use of cooking oils. Sunflower and corn oils are rich sources, for example.
However, consumption of omega-3s has remained fairly stable and there is much scientific debate about whether increased consumption, particularly if replacing saturates, might benefit our health. Good sources are some nuts and seeds and oily fish. Early clues as to possible benefits came from studies on traditional Greenland Eskimos who, despite having high fat diets, had low incidence of heart disease.
Closer inspection revealed that the fat in their diet was largely 'marine' i.e. from marine mammals (such as seals and walrus) and oily fish. This marine fat is high in omega-3s, which we now know have strong anti-blood clotting properties and help to guard against clots which can precipitate heart attacks and strokes. Further research has also revealed that they can help to keep the heart beat regular and reduce risk of 'arrhythmias' which can sometimes escalate into heart attacks, particularly in middle and old age.
Fatty acids vary in their carbon chain length, but very long chain omega-3s (particularly eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids) are also important in brain structure and function. Although these can be made in the body from shorter chain omega-3s (e.g. from plant origin) the conversion is not very efficient and varies considerably between individuals.
One way of boosting supply is to eat oily fish, such as sardines, mackerel, herring, salmon, trout and fresh tuna (canned tuna has lost most of its fish oil in processing). So women in pregnancy are recommended to eat one or two portions of oily fish per week (apart from shark, swordfish and marlin) and other adults up to four.
Fish liver oil supplements are not recommended in pregnancy because of the high vitamin A content which could harm the baby, if in excess. However, some respectable studies in recent years have reported beneficial effects of fish oil supplementation in children with hyperactive-type disorders, although further research is needed to confirm this.
Omega-3s may also have benefits in ameliorating symptoms in some 'inflammatory' disorders such as inflammatory bowel disease, asthma, eczema and rheumatoid arthritis. Incidence of these is lower in high fish-eating populations but, again, further research is needed to confirm or deny any links. However, the UK population does not eat a lot of oily fish and some people are never likely to!
So possible alternative ways of supplying these fatty acids are being investigated by scientists, such as supplementing feeds of cattle and poultry with fish oils; fortification of foods with algal sources; and genetic engineering of certain oil-seed plants to boost content of these fatty acids.
Meanwhile, we should not lose sight of old nutritional wisdom, which is still as relevant as ever - moderation and variation lead to a healthy body!
University of Huddersfield
www.hud.ac.uk
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