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Understanding Cholesterol

Everyone knows that having high cholesterol is bad... or is it? Health journalists talk about good cholesterol, bad cholesterol, saturated fats, poly un-saturated fats, mono-unsaturated fats and trans-fats; the list is endless. All this jargon makes cholesterol difficult to understand and can leave patients confused as to what a healthy diet really is.

Fats, or more accurately lipids (fats, cholesterol and other similar molecules), are crucial to life. In particular they are important in:

Forming the walls of every cell (the building blocks of life itself)
Storing energy
Producing hormones

Because fats are essential to life, the focus should be to ensure we eat the right types of fat in our diet, which promote health and wellbeing.

Lipids

When you see your doctor and request a cholesterol test, in actual fact they request something called a blood lipid profile. Lipids are a broad group of naturally occurring molecules. The lipid group is made up of the following subgroups:

Fats (Triglycerides)
Sterols (Cholesterol is an example)
Others (phosopholipids, glycolipids, fat soluble vitamins, waxes etc.)

Low Density Lipoproteins (LDL's or “bad cholesterol”)

We all know that oil and water don't mix. Blood is mainly water. Lipoproteins are rafts that carry fats through the blood to the different tissues in the body. LDL's are a type of lipoprotein that has been shown to increase the formation of atheroma (fatty plaques) inside arteries which increases your risk of angina or even heart attacks.

High Density Lipoproteins (HDL's or “good cholesterol”)

HDL's are another type of lipoprotein. They carry cholesterol from cells and take it back to the liver for further processing or removal from the body in bile. HDL's have been shown to decrease atheroma formation. Therefore HDL's are seen as being protective, preventing heart attacks and strokes. HDL's can be increased by exercise.

Triglycerides

Triglycerides are the main dietary fats. There are two main groups of triglycerides: saturated and unsaturated fats. Saturation refers to the amount of hydrogen stuck to the triglycerides. Your blood test will measure the total concentration of triglycerides but normally does not separate this into saturated and unsaturated sub-types.Generally speaking if your triglyceride level is very high and your HDL (good cholesterol) level is low, this can increase your risk of heart attacks and strokes.

Saturated fats

In general, saturated fats are found in animal and dairy sources. They tend to be solid at room temperature (like butter, ghee and lard). These fats are best avoided, as they raise all of your lipid levels (good and bad). This includes your total cholesterol, LDL, HDL and triglyceride levels.

Unsaturated fats

Naturally occurring unsaturated fats have a good effect on your blood lipid profile. They tend to be oils at room temperature. Unsaturated fats can be subcategorised into monounsaturated and polyunsaturated fats. Olive oil and canola oil are predominantly higher in monounsaturated fats. Monounsaturated fats help lower your total cholesterol, lower your LDL (bad cholesterol) and do not lower your HDL (good cholesterol). Oils high in polyunsaturated fats are a close second to monounsaturated fats. They also lower your LDL, but unfortunately, they will also lower your HDL.

Essential fatty acids

Other examples of healthy fats are the omega 6 and omega 3 essential fatty acids. Our bodies do not manufacture these, so they must be obtained through diet. Essential fatty acids can be found in oily fish and certain seed types (like flax seed). These fatty acids have a beneficial effect on our blood lipid profile and should be an essential part of our diet. According to the American heart association, they have been shown to:

Decrease risk of arrhythmias, which can lead to sudden cardiac death
Decrease total triglyceride levels
Decrease growth rate of atherosclerotic plaque (fatty plaques)
Lower blood pressure (slightly)

Trans-fats

The term “trans-fats” can be confusing. Trans fats are unsaturated fats that have undergone an industrial process known as partial hydrogenation. Partial hydrogenation chemically alters the shape of the unsaturated fats in such a manner that they tend to have a longer shelf life like saturated fats but remain oils like unsaturated fats at room temperature. That may be good for the fast food industry but it's not good for you heart.

While saturated fats and trans-fats both raise your LDL (bad cholesterol), trans fats also lower your HDL (good cholesterol). Trans fats are even worse than saturated fats, in terms of increasing your risk of heart disease(1). It would be wise to avoid trans-fats completely and some prominent doctors are recommending they should be banned from food production completely.

In the UK, companies are not obliged to state whether their produce contains trans-fats. If the food contains hydrogenated fats, like cakes and biscuits, then be wary. Try and avoid food labelled with the following words:

Hydrogenated
Partially hydrogenated
Shortening

Total cholesterol

Cholesterol is a molecule which is made in the liver. Humans produce an average of 1000 mg of cholesterol daily. Dietary sources of cholesterol are found in animal sources such as meat, liver, eggs and seafood (though eggs and seafood are low in saturated fats).

Studies show that our dietary intake of cholesterol has very little effect on our blood circulating cholesterol(2). In general, trying to alter your dietary cholesterol will be of minor significance unless you have diabetes or existing heart disease. It is much more important to concentrate on lowering your dietary intake of saturated fats, rather than to focus on the cholesterol levels in food.

So what changes can I make?

Don't focus on eliminating fats, which are crucial to life. Instead, concentrate on eating the right type of fats. Eating the right type of fats can actually lower the risk of cardiovascular disease. Here are some pointers:

No more than 1/3 of your daily calorie intake should come from fats.
Of those fats, 1/3 should be made predominantly of healthy unsaturated fats.
Stop cooking with animal fats like lard.Go easy on full-fat dairy and cheese.
Eat red meat only once a week and buy lean cuts.
Eat oily fish like salmon, mackerel and tuna, at least 3 times a week.
If you don't like fish, try adding flax seed in to your diet.
Use oils with high levels of monounsaturated fats, like olive oil.
When cooking, avoid deep-frying. Rely on baking and grilling instead.
Use healthy oils in dressings.
Avoid excessive carbohydrates (sugars/ starch). These are converted into excessive triglycerides.
If you are at high risk of heart disease, go for egg whites rather than whole eggs.

Prevention is the best cure. Our diet can play a significant part in our health and wellbeing. Learning more about what our foods contain should helps us make more informed health choices and reduce the incidence of cardiovascular diseases like heart attacks and strokes.

Sources

1. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Trans fatty acids and cardiovascular disease. New England Journal of Medicine, 354(15), 2006, pp.1601-13.

2. Kratz M. Dietary cholesterol, atherosclerosis and coronary heart disease. Handbook of Experimental Pharmacology, 170(2), 2005, pp.195-213.

3. Stryer, L. Berg, J.M. Tymoczko, J.L. Biochemistry. 5 ed. W.H.Freeman & Co Ltd, 2002.

Author: Dr Shazan Chughtai, MB BS

Editor: Dr Hanny Anwar BMedSci, MB BS, MRCS

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