What is cholesterol?
Cholesterol, like many food-related molecules, has previously been given a bad rap. Whilst there are ‘good’ and ‘bad’ types of cholesterol, cholesterol remains an essential molecule in the body, composing the cell membrane and maintaining its structural integrity, as well as being the precursor for steroid hormones, such as progesterone, testosterone, estradiol and cortisol.
“The human body produces around 80% of the cholesterol required to maintain vital processes, with the remaining 20% being consumed from the diet.”
Without cholesterol, our bodies would struggle to produce the aforementioned hormones, which could lead to issues with maintaining pregnancy, for example, whereby caucasian women with low serum cholesterol have an increased risk of premature birth, and low birth weight (1).
Types of Cholesterol
Cholesterol on its own is insoluble in blood, and so to be transported to where it needs to be in the body, it binds to molecules called lipoproteins. There are five types of lipoprotein in total, but only two are involved in the transport of cholesterol.
- High Density Lipoprotein (HDL) – “good cholesterol”.
- Low Density Lipoprotein (LDL) – ‘bad’ cholesterol”.
Both types are vital for day-to-function.
- HDL cholesterol transports cholesterol to the liver, where it is converted into bile salts, then bile, and then expelled from the body.
- LDL cholesterol circulates in the blood and transports cholesterol to where it is needed, so the body can produce sex hormones, vitamin D, and cell membranes – all vital processes for a healthy body.
However, the issue with LDL can lie when there is an excess of cholesterol.
Cholesterol in the Body
The human body produces around 80% of the cholesterol required to maintain these processes, with the remaining 20% being consumed from the diet (2). The liver synthesises cholesterol, and LDL transports it from the liver, to where it is needed, as outlined above.
If there is an excess of cholesterol consumed, the liver will produce more than what is needed. Cholesterol cannot stay in the liver, and so is exported by LDL. When the cells that require cholesterol have received all that is required, they cannot uptake more. This, therefore, requires the cholesterol to be eliminated in some way.
“An excess of cholesterol deposited by LDL, that is not able to be eliminated by HDL, can impose health risks.”
Unfortunately, it can’t be given straight to HDL to be taken back to the liver and expelled. LDL deposits the excess cholesterol in the lumen of the arteries. If there is a suitable level of HDL in the blood, the deposited cholesterol will be transported back to the liver and removed from the body. However, if there is a large amount of cholesterol deposited and/or insufficient HDL to get rid of it, it can result in the cholesterol hardening to form a plaque, which can restrict the flow of blood around the body, therefore also reducing the amount of oxygen to organs, hence why cholesterol has previously been linked to heart problems, clots and strokes, as plaque formation can often result in these (3).
So, while both HDL and LDL are essential, an excess of cholesterol deposited by LDL, that is not able to be eliminated by HDL, can impose health risks, hence when LDL is known as ‘bad’ cholesterol.
Changing your Cholesterol Levels
If you are worried that your cholesterol levels are too high, or have been explicitly told that they are, you can combat the issue yourself through diet and exercise.
“Dietary cholesterol (for example, from eggs) has a much smaller impact on your blood cholesterol levels than the fat it is eaten with.”
Reducing the amount of saturated and trans fats consumed (such as those in cake, red meat, and cream for example), replacing them with unsaturated fats (such as those in nuts, fish and olive oil) can make a huge impact on your cholesterol levels. Some fibre has also been found to reduce cholesterol levels, so aim to up the amount of fruit and veg consumed, too. And lastly, at least 150 minutes of moderate aerobic activity (i.e. enough to raise your heart rate and break a sweat) a week, can aid in reducing your cholesterol too. That’s only around 20 minutes a day!
What is important to note, is that dietary (for example, from eggs or prawns), has a much smaller impact on your blood cholesterol levels than the fat it is eaten with, hence why reducing your saturated fat intake can make such a big difference.
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References:
1. Adverse Birth Outcome Among Mothers With Low Serum Cholesterol. Robin J. Edison, Kate Berg, Alan Remaley, Richard Kelley, Charles Rotimi, Roger E. Stevenson, Maximilian Muenke. Pediatrics Oct 2007, 120 (4) 723-733; DOI: 10.1542/peds.2006-1939
2 How it’s made: Cholesterol production in your body. Julie Corliss. Harvard Heart Letter. [ONLINE] Accessed on: 13/07/20. Available here.
3. Biochemistry, 8th edition. Jeremy M. Berg, Lubert Stryer, John Tymoczko, Gregory Gatto. ISBN 10: 1319114652 / ISBN 13: 9781319114657 Published by WH Freeman, 2015
