Lets talk about the Cholesterol.. Is it good, is it bad or what about both good and bad. Definitely not fair to say it is ugly. After reading more and more about the stuff, I have come to the conclusion that it is not only good, but vital. However, it can be led astray by its chauffeur, giving it the bad reputation it has. Lets use a rubbish collection service and postal service analogy to explain, with some fly-tipping thrown in too!
First, we will start with explaining what cholesterol is and what it does?
Cholesterol is a fat and if you held it in your hand it would resemble very fine scrapings from a whitish-yellowish candle, i.e a waxy substance.
Due to its waxy nature, it is a terrible swimmer. If it were to jump into our rivers of blood it would quickly curdle up into useless blobs. This is the reason why the body has a postal service to transport cholesterol to its many destinations. The envelopes for cholesterol are protein covered molecules, lipoprotein being the major one and it has no problem mixing with blood and water.
Cholesterol is so important to our body that mother nature did not put all her eggs in one basket and rely on us humans to collect enough cholesterol from our diet, instead the body is able to manufacture the approximate 1000mg of cholesterol that it needs to function properly.
Cholesterol is a vital brick in the walls of cells. In liver cells, cholesterol accounts for 30% of the cell wall components. Within the cell walls, cholesterol plays a role in stability, allowing the cell to maintain its function over a wide range of temperatures. Cholesterol also acts as a cell wall insulator preventing the leakage of ions out through the cell wall.
Cholesterol is used in the production of bile acid, which is important for the breakdown and digestion of our food in the intestines.
Without Cholesterol, we would not exist. Now how do you feel about the C word that gets a lot of bad rep?
Lets quickly crack the myth that eating lots of eggs raises our cholesterol levels. As we mentioned earlier, most of the bodies cells can make their own cholesterol, the liver especially, it is a cholesterol powerhouse that can afford to export most of what it makes. So if the body brings in more cholesterol through the diet, in the form of eggs for eggsample, then the liver will decrease its production. Supply and Demand. This results in the total body cholesterol changing very little if at all.
How food becomes cholesterol and how it is transported around the body?
After eating a meal, the food is broken down by enzymes and acids throughout its journey. In the small intestine, fatty acids are bundled together to form triglycerides, these then hook onto a cholesterol and a protein to form a chylomicron. This is part of the postal service, building a package fit for export. There are two main post offices in the body, here in the small intestine and in the liver.
Escape to freedom! Chylomicrons, some spare fatty acids and glucose leave the small intestine, are absorbed into the blood and travel to every organ in the body. The Chylomicrons stop off at the liver to drop off some cholesterol for repackaging. This is of course when Insulin Incorporated dispatch the glucose sales team to encourage the uptake of glucose into the bodies cells. (See last month’s blog if you are slightly confused right now!).
Meanwhile, at the Central Post Office HQ in the liver, the staff are busy collecting the carbohydrates and proteins that were released by the small intestine. They have the machinery to convert these into tryglycerides (three fatty acids and a glycerol molecule) and then package the tryglycerides with proteins and cholesterol, to produce something transportable called a very low density lipoprotein (VLDL). These VLDLs or postal delivery vans enter the bloodstream and travel with the chylomicrons delivering triglycerides to the cells for storage. To do this, they pull into the driveway of the cell without crashing into the cell wall! The VLDL or Chylomicron driver hoots the horn to signal enzymes from the muscle cell or fatty tissue cells to come out and unpack most of the triglycerides and bring the load back into their cell. Triglycerides are used as energy in muscle cells and are stored as an energy source in fatty tissue cells.
Both chylomicrons and VLDLs become more and more dense as they give up their low density fatty cargo. Eventually, all that remains is the van, i.e the cholesterol and protein packaging, and a fraction of the original triglyceride. Chylomicron drivers stick an empty load sticker on the van so that the liver can recognise them. The liver takes these back and uses them again in the future.
Many of the triglyceride depleted VLDL vans keep circulating and eventually become Low density Lipoproteins (LDLs) once their triglyceride parcels have all but gone. LDLs are now transporting cholesterol as their main product, they consist of roughly 45% cholesterol at this stage and are responsible for transporting 60-70% of the body’s cholesterol. Virtually all cells in the body can take up and use LDLs for their individual needs.
It is this LDL cholesterol that is given the bad name, as you will have heard on many TV adverts. However, LDL’s come in different sizes and densities. The larger less dense are not as prone to fly-tipping as the smaller and more dense LDL’s. By fly-tipping, I mean leaving their luggage in the blood vessels, which can then lead to athersclerosis or hardening of the arteries. The reason why the more dense LDL’s can get stuck in the arteries and deemed “bad” cholesterol is because they are smaller and so can travel from the blood stream into the blood vessel a lot easier then the larger LDL. More importantly and unfortunately, they are more susceptible to oxidation, especially if there is consistent high blood sugar levels (check out the December blog for info on oxidation and January blog for tips on controlling blood sugar levels) which can result in them sticking to the arterial walls and becoming an unsightly mark on the landscape, hence the fly-tipping analogy. The body then releases its immune defense cells called macrophages to clean up the mess, they operate like pac-men and engulf the oxidised LDL’s. They over-indulge and become too enlarged to escape back through the blood vessel cell wall and so become trapped along with the LDL’s. The LDL’s undergo more oxidation and so more Macrophages come to the rescue, which leads to a build up of plaque deposits. These deposits can narrow the artery over time.
What can be done about this?
The body has a rubbish collection service by the name of HDL cholesterol. The rubbish trucks or HDL are made in the liver and intestine and have two main jobs. They get out there and give the chylomicrons and VLDL’s the proteins or stickers that they use to alert the liver to attract them back to HQ so that they can be recycled. The other job is called Reverse Cholesterol Transport. This involves the rubbish trucks scouting the blood stream in search of extra cholesterol LDL’s that is not needed by the cells or tissues and delivers them back to the liver where they are used to produce bile or are recycled.
This explains why high levels of HDL are associated with low risk of heart disease.
How do we increase our HDL levels?
Lifestyle changes affect HDL levels, Exercise increases HDL count while obesity and smoking lower them. There is mounting evidence to show that interrupting time spent sitting with regular standing breaks or light intensity walking has a positive effect on HDL cholesterol, lowers LDL and blood glucose levels. A hugely important finding from these studies is that even meeting the guidelines for physical activity, i.e 150 mins/week of moderate to vigorous activity does not protect you from the poor health effects from sedentary behaviour. I like to use Homer Simpson as an example in this case. Homer gets up at 7am, goes for a 30min jog, then gets in the car to drive to work, pretends to work all day in a reclined position, gets back in the car to drive to springfield, then gets his kicks on the couch for the evening. According to the World Health Organisation, Homer meets the Physical Activity Guidelines, I am sure we all agree that he is not exactly a healthy human in prime condition! Besides the fact he is not even human! What about the other 98% of the day, how sedendary are you, and if so, think of ways of breaking the sitting habit. Get up during the adverts, place your bin further away from your office desk to encourage regular sedentary interruption. Pick up a pedometer and ensure you meet your daily step goals, or use a pedometer app on your smart phone. Check out the nicely put together movie by Dr Mike Evans called 23.5 hours.
Cholesterol lowering medication called statins work by preventing the production of cholesterol by the cells, causing the cells to pull in LDL from the bloodstream in order to feed their cholesterol needs.
If we leave it there for this Month, hopefully you are all now more aware of how cholesterol is made in the body and how it is absorbed from the food and the difference between HDL/LDL and VLDL.
Next month we will continue the focus on fats by using a court case trial as an analogy.
Thanks for reading
Nutritionist and Chartered Physio