Tuesday, April 5, 2011

Dietary Fats

Fats provide energy and components for some structures, such as cell membranes and certain hormones. The basic building blocks of dietary fats are fatty acids, which consist of chains of carbon atoms with hydrogen atoms attached.

There are three main natural forms of fatty acid. Saturated fatty acids are so called because they have as many hydrogen atoms as they can hold.Monounsaturated fatty acids lack a pair of hydrogen atoms per molecule. Polyunsaturated fatty acids lack four or more hydrogen atoms per molecule.

Saturated fatty acids

These are found in animal products, such as butter, cheese, whole milk, ice cream and meat, and in some vegetable oils, such as coconut and palm oils. It is often said that eating a diet rich in saturated fatty acids can raise levels of cholesterol in the blood. However, more than one study has found that this may not be the case. Even the belief that such a diet is a major risk factor for coronary artery disease may be overstated, partly as a result of misquoting and misinterpretation of research studies. Saturated fatty acids

may be a factor in weight gain and obesity, although a comprehensive review of the subject concluded that dietary fat is not a major determinant in body weight, and eating less fat is unlikely to bring lasting weight loss.

So, on balance, it appears that saturated fatty acids might be less harmful than is often believed, and that eating them in moderate amounts may not be damaging to health.

Monounsaturated fatty acids

Food rich in monounsaturated fatty acids include olive oil, avocados, nuts and seeds. These fatty acids can lower blood levels of low-density lipoprotein (LDL) cholesterol, the type of cholesterol that is believed to increase the risk of heart disease.

They can also raise blood levels of highdensity lipoprotein (HDL) cholesterol, which is thought to protect against heart disease. A high intake of monounsaturated fatty acids is believed to be one of the reasons

certain populations, such as the southern Italians and the Greeks, have relatively low levels of heart disease.

Polyunsaturated fatty acids (PUFAs)

There are two main groups of PUFAs in the diet: omega-6 and omega-3. The major omega-6 fatty acid is linoleic acid – rich sources include plant oils, such as hemp, pumpkin, sunflower, safflower, sesame, corn, walnut and soya oil. Others are gamma linolenic acid (GLA), dihomogamma linolenic acid (DGLA) and arachidonic acid (AA).

The major omega-3 fatty acids are alpha-linolenic acid (from plants, such as flaxseed), eicosatetraenoic acid (ETA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA are mainly found in oily varieties of fish.Within the body, these fatty acids can be converted into other substances that may affect health.

The omega-6 and omega-3 balance

The omega-3 and omega-6 fatty acids have important roles in many body systems, including the brain, nerves, immune system, cardiovascular system, eyes and skin. They are converted into hormone-like substances called eicosanoids. Eicosanoids derived from omega-6 fatty acids tend to encourage inflammation, blood-vessel constriction and blood clotting.

Therefore, they increase the risk of coronary artery disease and stroke and inflammatory conditions,

such as arthritis. Eicosanoids derived from arachidonic acid are particularly potent. Those from omega-3 fatty acids, such as EPA, are less likely to encourage inflammation; some are positively anti-inflammatory.

They tend to reduce the risk of clotting and help to relax blood vessels, so helping to reduce the risk of coronary artery disease and stroke as well as inflammatory conditions, such as arthritis. The roughly opposing actions of omega-3 and omega-6 fatty acids mean that it is important to balance their intake.

A ratio of 1:1 is believed to be ideal. Over the past 40 years, however, the proportion of omega-6 to omega-3 in the average diet has increased to roughly six to one. This may be an important factor in the development of many chronic diseases, such as cardiovascular disease and cancer.

To reduce your intake of omega-6 fatty acids and increase your intake of omega-3 fatty acids:

Limit the intake of vegetable oils, such as sunflower oil, corn oil, rapeseed oil and maize oil, which contain omega-6 fatty acids. Processed foods labelled as containing “vegetable oil” contain these oils.

Sprinkle flaxseeds on cereals and take flaxseed oil, which is a rich source of omega-3 fatty acids.

Eat three portions a week of oily fish, such as mackerel, herring, salmon, trout and sardines.

Take a fish oil supplement each day.

Partially hydrogenated and trans fatty acids

Some margarines and vegetable shortenings (the fats added to many processed foods) are manufactured using a process known as hydrogenation. This can change the structure of fats, creating what are known as trans fatty acids. These are believed to have harmful effects on health, particularly with regard to heart disease.While trans fats do occur naturally in some foods (such as butter), there is evidence that it is only industrially produced, and not naturally occurring, trans fats that have a detrimental effect on heart health.You should consider avoiding margarines and processed foods listing partially hydrogenated oils (or

trans fatty acids) as an ingredient.

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