Diet and Coronary Heart Disease

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Health Risks Caused by Obesity

Up to 30 000 deaths a year in the UK are considered to be obesity related. Obesity is thought to be the most important dietary factor in the following health problems:

cancer

cardiovascular disease

type 2 diabetes

Obesity is also linked to:

gallstones

oesteoarthritus

high blood pressure (hypertension)

Other Components of the Diet

There are many aspects of the diet that can affect your health. Here we are concerned with components that may affect the risk of CHD. CHD is the result of deposition of fatty substances in the walls of the coronary arteries. This deposition is known as atherosclerosis, reduces the size of the lumen, this restricts blood flow to the heart muscle and may cause oxygen stravation.

Salt

Excess salt in your diet will decrease the water potential of your blood. As a result more water is held in the blood and blood pressure increases. This can lead to hypertension. Hypertension is a condition in which the blood pressure, and particularly the diastolic pressure (heart at rest) is maintained at a level that is too high. Hypertensions can damage the inner lining of the arteries, which is one of the early steps in the process of atherosclerosis.

Fats

Fats are an essential part of the diet. Animal fats tend to be saturated and plant oils tend to be unsaturated. In general it is recognised that saturated fats are more harmful then unsaturated fats. Polyunsaturated fats and monounsaturated fats, such as those found in olive oil, are particularly beneficial to health.

Cholesterol

Cholesterol is not a triglyceride but it has similar properties. It is found in many foods and is often associated with saturated fats in meat, eggs and dairy products. Cholesterol is also made in the liver from saturated fats. Too much cholesterol in the blood is harmful. High blood cholesterol concentrations have been linked to 45-47% of deaths from coronary heart disease. The concentration of cholesterol in the blood should be maintained below 5.2mmoldm-3.

Why is cholesterol in the blood?

Cholesterol is essential to the normal functioning of the body. It is found in cell membranes and in the skin. It is also used to make steroid sex hormones and bile. Therefore cholesterol must be transported around the body. Like all the fats, cholesterol is not soluble in water. It must first be converte to a form that will mix with water. Cholesterol is transported, in the blood in the form of lipoproteins. These are tiny balls of fat combined with protein. There are two types of lipoprotein:

high-density lipoproteins

low-density lipoproteins

Both types of lipoprotein are released into the blood and can be taken up by cells that have the correct receptor sites.

High-Density Lipoproteins

HDLs are produced by combination of unsaturated fats, cholesterol and protein. These tend to carry cholesterol from the body tissues back to the liver. The liver cells have receptors that allow the HDLs to bind to their cell surface membranes. In the liver the cholesterol is used in cell metabolism (to make bile) or is broken down. Therefore, high levels of HDLs are associated with reducing blood cholesterol levels. They reduce deposition in the artery walls by atherosclerosis and may even help to remove the fatty depositions of atherosclerosis. Since HDLs use unsaturated fats these fats are thought to be more beneficial to health than saturated fats.

Low-Density Lipoproteins

LDLs are produced by the combination of saturated fats, cholesterol and protein. These tend to carry cholesterol from the liver to the body tissues. The tissues have receptor sites that allow LDLs to bind to their cell surface membranes. If too much saturated fat and cholesterol is consumed in the diet the concentration of LDLs in the blood will rise. A high blood concentration of LDLs causes deposition in the artery walls. Different fats affect the LDL receptors in a number of different ways.

Saturated fats are thought to decrease the activity of the LDL receptors. Therefore as blood LDL concentration rises, less is removed from the blood. Theis results in higher concentrations of LDL in the blood and they are deposited in the artery walls.

Polyunsaturated fats seem to increase the activity of LDL receptors and so decrease the concentration of LDL in the blood.

Monounsaturated fats also seem to help remove LDLs from the blood.

Diet and Lipoproteins

Our diet has a significatn effect upon the lipoprotein concentration in our blood. Overall it is best to keep to a low-fat diet which will maintain low-density lipoprotein concentrations. The ratio of HDL to LDL in the blood is very important. Since LDLs are associated with greater deposition in the artery walls it is best to try to maintain a low proportion of LDLs. HDLs are associated with reduced deposition so it is best to maintain a high proportion of HDLs in the blood.

Eating a lot of saturated fats will increase the concentration of LDLs in our blood.

Eating a low-fat diet will reduce the overall concentration of lipoproteins.

Eating a high proportion of unsaturated fats will increase the proportion of HDLs in the blood.

Eating polyunsaturated fats helps to reduce the concentration of LDLs in the blood.

Eating monounsaturated fats helps to reduce the concentration of LDLs in the blood.

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