4 Diet, exercise and cholesterol
Cholesterol is a type of fat that is often given bad press due to its role in developing Coronary Heart Disease (CHD). However, it is produced and used by the body for a range of functions. In fact, cholesterol is so important that it is produced by the liver to meet your daily needs. If you consume foods containing cholesterol though, your liver will make less to compensate for this. The problem comes when you consume more than is needed to meet the requirements of the body.
Cholesterol performs the following functions:
- helps to form the structure of the cell membranes
- produces bile, which aids fat digestion
- produces steroid hormones such as oestrogen and testosterone
- produces vitamin D from sunlight.
Cholesterol is found in the same foods as saturated fats. Meat, poultry, egg yolks, seafood and dairy products are all sources of cholesterol.
Low-density lipoproteins (LDLs) carry cholesterol from the liver to the tissues where it is needed. High-density lipoproteins (HDLs) are responsible for the removal of surplus LDLs from the tissues to be taken back to the liver for disposal (Figure 4). Therefore, HDLs are regarded as good cholesterol and LDLs as bad cholesterol.
Blood cholesterol level is measured in millimoles per litre (mmol/l), and this can be measured through a simple blood test. There is cause for concern if the measure of blood cholesterol is over 5.2 millimoles per litre. However, it is important to know the ratio of LDLs to HDLs as well: it should be 75 per cent LDL to 25 per cent HDL. If the amount of LDL is more than 75 per cent, then there is also an increased risk of CHD. It is possible to have a low blood cholesterol level but still be in danger if the HDL count is less than 25 per cent.
There are clear guidelines as to what are acceptable cholesterol levels and levels associated with an increased risk of CHD. These levels are shown in Table 1. Excess amounts of cholesterol in the blood can increase the risk of cholesterol being deposited onto the artery walls. As the cholesterol is laid down in the artery walls, the artery space will start to narrow and it will cause a hardening of the artery wall. The resulting loss of elasticity to the artery wall and smaller space to transport blood is the start of CHD and can cause angina.
| Blood cholesterol level (mmol/l) | <5.2 | 5.2–6.5 | 6.5–7.5 | >7.5 |
| Risk of CHD | Low | Increased | Moderate | High |
HDL count is increased by taking regular exercise and is lowered by smoking and increasing exposure to pollution. LDL count is raised through excess alcohol intake and high consumption of foods rich in saturated fat.
In the following activity, you will learn about the effects of diet and exercise on blood lipids.
Activity 3 Blood lipids
Read from ‘Reduced blood lipids’ up to, but not including, the subsection ‘Increased lean tissue’ on pages 326–329 from Chapter 13 of the book Fitness and Health by Sharkey and Gaskill (2013) [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] :
As you read, answer the following question:
- What effect does diet and exercise have on the blood lipids - triglycerides and cholesterol?
Discussion
- Both dieting and exercise can reduce blood plasma triglyceride levels. Exercise enhances the removal of triglyceride from the circulation and increases its utilisation in the muscle cells. Exercise also helps to shift the balance or profile of lipoproteins in the blood, raising HDL and lowering LDL. Therefore, regular physical activity provides a very substantial health benefit.
In the next section, you will move on to consider the importance of nutrition before, during and after exercise.