The word ‘cholesterol’ almost strikes fear in the public, but I feel it is often misrepresented by the media, and usually surrounded by pseudo-science and hearsay, which makes a lot of information contradictory and confusing. Here I will explain what cholesterol is, what it does in the body and why it has developed such a bad name.
What IS cholesterol?
Cholesterol doesn’t belong to a macro-nutrient group such as fats, nor does it belong to the micro-nutrients group as vitamins do. Cholesterol belongs to its own distinct group in food chemistry call ‘sterols’. These sterols have a number of roles in the body, and are pre-cursors for a number of hormones and other essential elements of the body. In short, sterols, including cholesterol are essential for health, and I will explain the role of cholesterol in greater detail below.
Role of cholesterol in the body
Cell membrane fluidity – Cell membranes are made up of 2 layers of phospholipids, which move in a fluid motion, and are not bonded to each other. Cholesterol molecules are embedded into the phospholipid layers, which increases the rigidity of the membrane. By adding or removing cholesterol from the cell membrane, the body can control how fluid the membrane is, and alter it to maintain the optimum level of fluidity. If for any reason (such as consumption of alcohol) cell membranes are getting too fluid, more cholesterol is added to them, and vice versa.
High Density Lipoprotein (HDL) and Low Density Lipoprotein (LDL)
HDL is also referred to as ‘good cholesterol’, and is responsible for removing cholesterol from the cell membrane to the liver to be excreted. This means that the cells that have had cholesterol removed will become more fluid, which is especially important for arteries, as this increased fluidity makes them more flexible. With the arteries being more flexible, there is less likely they can be damaged from blood pressure. It has been regularly observed that high levels of HDL are linked to a low risk of heart disease.
LDL is referred to as ‘bad cholesterol’, it does the opposite job to HDL and adds cholesterol to the cell – making the cells more rigid. Rigid cells will be less able to absorb the pressure of blood, and so are more likely to be damaged. A link has been repeatedly observed between raised LDL levels and an increased risk of heart disease.
Natural Production/ Distribution Disrupted
Foods high in sugar (particularly foods sweetened with fructose) are linked to increased LDL levels. We know that fructose can only be metabolised by the liver, and so high levels of fructose in the diet could result in irregular liver function, but the mechanism by which this occurs is not yet fully understood. Short chain saturated fatty acids (SCFA) are also associated with raised LDL levels, and this again could be due to an interaction with the liver and these SCFA’s, but like with fructose, the mechanism is yet to be fully understood.
The Body Cannot Break Down Cholesterol
If there is too much cholesterol in circulation in the body, the body will dispose of it in order to maintain homeostasis. The body cannot break down cholesterol, and so disposes of it by passing it into the intestine where it will be excreted in the stool. Once in the intestine, it can be incorporated by the stool and/or the bacteria which inhabit the gut. However, if this does not happen, the body will reabsorb the cholesterol which will result in raised levels of circulating cholesterol.
Inability to hold cholesterol in the intestine can occur as a result of two factors. The first is that there is not enough dietary fibre being consumed. This means that the stool cannot form properly and the excess cholesterol cannot be held, which will result in re-absorption. The second factor is low levels of probiotics inhabiting the digestive tract, especially lactobacillius spp. This could be a result of infection, food poisoning or antibiotic use. Lactobacillius spp. can incorporate any cholesterol into their cells and convert it into coprostanol. This prevents ‘lose’ cholesterol in the intestine being re-absorbed into the body. There is a limited amount of cholesterol which Lactobacillius spp. can incorporate, and so probiotics cannot substitute fibre for this purpose.
Cholesterol is an essential nutrient in the body which can be obtained from diet, but is mainly synthesised in the body by the liver. Its primary role in the body is to control cell membrane fluidity, and is transported to the cell in LDL and away from the cell in HDL. Diet has a large influence on the amount of cholesterol which is in the cell membrane. In order to help the body regulate cholesterol properly, alcohol should not be frequently consumed, sweetened/ high sugar foods should be avoided, sources of SCFA should be controlled and a regular intake of fibre should be consumed. It is also important to avoid antibiotics where possible, or take probiotic food/ supplements after a course of antibiotics.