Dietary fats are varied in origin, such as your obvious 'visible' fats like butter, margarine, cooking oils and the fat that surrounds your juicy steak.
There are also many 'invisible' fats such as those in nuts, cakes, biscuits, ice-cream, tinned or packet foods, cheese and many other animal and vegetable sources that you may sometimes forget about, not know of or choose to ignore.
Good fat or bad fat?
Polyunsaturated, saturated and monounsaturated generally are the three main categories of fat. All fats contain a mixture but predominantly contain one type; for example, virgin olive oil is mainly made up of monounsaturated fat.
We need fatty acids in the body to build new cells and essential for the communication of nerve impulses and for normal brain development. It's no surprise that it is said that takeaway food (I'll mention no leading names here) is fuel for 'dummies'.
Not that going to a takeaway on occasion will make you stupid, but replacing healthy fats from nuts, seeds, oily fish, lean meats and such with takeaway or processed foods too often is going to leave you undernourished in the essential fats required to feed your brain.
Essential fatty acids (EFA's) are fats that are essential to the body and that the body cannot produce (therefore essential). These are Linoleic acid (LA) which are Omega 6 fats, while Omega 3 fats are Linolenic (LNA). The body can then make other fatty acids from these. However, the ability of Omega 3's to make other fatty acids can be disrupted if the balance of Omega 6's are too high as while performing their conversions, they both require (and compete) for the same enzymes. Good sources of omega 3's are oily fish and flax oil. Omega 9 is also a good source of fat, more often used in the form of virgin olive oil.
The extensive use of polyunsaturated oils in cooking and food manufacturing make Omega 6's more prevalent in the diet. This is why the emphasis on the importance of Omega 3's in the media and by health professionals in recent years has become so prominent.
EFA's are essential for the movement and manufacture of energy in the body and regulating oxygen transport. They are also vital for blood clotting,maintaining cell structure and supporting the immune system as well as synthesizing hormones.
Triglycerides are a type of fat that circulates in the blood and are used for energy. A risk of heart disease is higher if triglyceride levels get too high, mostly from being overweight or eating too much of the wrong fats.
A study done at the Rockefeller University, New York, concluded that a diet high in saturated fat activates circulating triglycerides as well as stimulates subsequent food intake.
Cholesterol has a very important role in the body. It is made by the liver and used in the synthesis of hormones including testosterone, oestrogen and cortisone. Cholesterol gives cells their rigidity preventing collapse; while EFA's keep them pliable. Bile and vitamin D are both made from cholesterol.
Too much cholesterol in the body can have damaging effects and is the main component responsible for building up on artery walls. The build up can cause poor blood circulation, leading to strokes and heart attacks. Actual cholesterol in foods has a lesser effect on cholesterol levels than a diet high in saturated fats or refined carbohydrates.
High density lipoprotein (HDL) is known as the good cholesterol and carries the fat containing cholesterol & triglycerides to the liver where it is metabolised. Low density lipoproteins (LDL) are known as the bad cholesterol due to its damaging effects when too high. All the bodies cells have LDL receptors and will close when they have met their cholesterol & triglyceride requirements. The remainder then circulates in the blood and either stored as fat or returned to the liver.
Trans fatty acids (TFAs) can also raise cholesterol levels, damage the heart, immune system, hormones and promote cancer. These are unnatural forms of fatty acids formed from unsaturated fats are exposed to heat and light after extraction such as in the making of margarine.
References:
Barson, JR. Karatayev, O. Gaysinskaya, V, Chang, GQ. Leibowitz, SF. (2011) Effect of dietary fatty acid composition on food intake, triglycerides, and hypothalamic peptides, Laboratory of Behavioral Neurobiology, The Rockefeller UniversityNewYork. Available: http://www.sciencedirect.com/science/article/pii/S0167011511001601, [20/10/2011].
Dunne, J Lavon. (2002) Nutrition Almanac, Fifth Edition, New York: McGraw-Hill.
Ministry of Agriculture, Fisheries and Food. (1995) Manual of Nutrition, Tenth Edition, London: HMSO.
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