There is a wealth of research to suggest that elevated blood cholesterol is a risk factor for Coronary Heart Disease (CHD).
Other risk factors include obesity and inactivity, so you are in an ideal position to help out; but do you really have the knowledge to do so? The following update examines the role of diet and exercise in the cholesterol controversy, providing information to help you implement current guidelines to advise your clients.
What is cholesterol? Cholesterol is a fat-like substance found in animal-derived foods. It is a member of a group of lipids called sterols and can be manufactured by the body, in the liver. If the diet is low in cholesterol, the liver makes more as necessary. Although cholesterol is often labelled as being ?bad?, it is an essential part of every cell in the body and is involved in the production of vitamin D and certain hormones, including oestrogen and testosterone. It is also used in the production of bile acids which are needed for the digestion of fats in the gut.
Factors affecting blood cholesterol - Genetics, family history - Dietary fat intake: saturated fatty acids raise blood cholesterol - Exercise levels - Central obesity (intra-abdominal fat) - Other factors, e.g., alcohol intake, smoking, anabolic steroids, high body mass index, age
Dietary cholesterol
The main dietary factor associated with high blood cholesterol is a high fat intake and the type of fat in the diet. A ?low? cholesterol diet simply aims to reduce the amount by reducing the intake of foods containing cholesterol (e.g., shell fish and egg yolks), although there is little correlation in healthy people between the intake of cholesterol and blood cholesterol levels. However, there is a strong link between this and the intake of saturated fatty acids since saturates raise the level of cholesterol in the blood.
Saturated, Poly-unsaturated and Mono-unsaturated Fats
Fats and oils in food are made up of units called fatty acids which can be classified as saturated, polyunsaturated and monounsaturated. All fats and oils contain a mixture of these three fatty acids. Saturated fats (SFA) are usually hard at room temperature and of animal origin. Some dietary sources are beef, butter, lard, cream, whole milk, eggs and cheese. Non-animal vegetable saturated fats are coconut and palm kernel oil, cocoa butter and non-dairy milk and cream substitutes.
Polyunsaturated fats (PUFA) are usually liquid at room temperature and of vegetable origin. They are found in nuts, seeds, meat and many vegetable oils and spreads made from them, e.g., corn, sunflower, safflower. The two main groups are the essential fatty acids linoleic (n-6 or omega-6 family) and alpha-linoleic acid (n-3 or omega-3 family). Current dietary intakes should not be increased.
Monounsaturated fats (MUFA) are considered to be a healthier option. Olive oil is high in MUFA. The high intake of MUFA in Mediterranean countries is thought to contribute to their low incidence of coronary heart disease.
The Effect of Diet Lipoproteins are carriers that transport fat and cholesterol through the circulation. There are several different lipoproteins: however, the two that are usually considered are called low-density lipoproteins (LDL) and high-density lipoproteins (HDL). LDL cholesterol is often termed ?bad? because high levels are associated with a greater risk of heart disease. HDL cholesterol is often termed ?good? as it helps to have a protective effect . Raised plasma cholesterol concentrations usually reflect elevated levels of LDL cholesterol. LDL is enriched in cholesterol and is the end product resulting from the transport of fat from the liver to the other tissues. Having delivered the fat to the tissues the remnant particle (LDL) is removed from the blood mainly by the liver.
The amount of LDL in the blood depends upon the rate at which it is synthesised and the rate at which it is removed from the blood. Upon reaching a certain concentration, LDL is taken up by macrophages (white blood cells) in the blood vessel wall. These then fill with cholesterol containing LDL, take on a foamy appearance and make up the fatty streaks seen in arteries. Some of these fatty streaks disappear and some go on to form atherosclerotic plaques.
Current research suggests that atherosclerosis may be prevented by anti-oxidant nutrients (including beta-carotene, vitamins C and E), possibly by preventing the oxidation of LDL cholesterol. PUFA in the LDL particle are susceptible to oxidation by the action of free radicals, which are highly reactive oxygen molecules. Free radicals are produced in the body as a by-product of normal metabolism and can also be taken into the body from the environment (e.g., via cigarette smoking, exhaust fumes, radiation)
Considering the potential damage that may occur when LDL cholesterol is oxidised, there is concern about diets with very high levels of PUFA. COMA has therefore set an upper limit of 10% dietary energy from n-6 PUFA. In other words, although partial substitution of n-6 PUFA for SFA helps to lower LDL cholesterol, it is considered unwise to tilt the balance too far. Anti-oxidant vitamins may help to reduce or prevent this oxidation and foods containing them should be increased in the diet.
Dietary sources of beta-carotene: carrots, tomatoes, red and yellow peppers, yellow and orange fruit and vegetables, green leafy vegetables.
Dietary sources of vitamin C: kiwi fruit, oranges, lemons, limes, green peppers, tomatoes, new potatoes, blackcurrants, strawberries.
Dietary sources of vitamin E: wholegrain breakfast cereals and bread, vegetable oils e.g., sunflower, almond, cheese, dairy products, margarine, eggs, avocado
Note that dietary cholesterol alone makes only a minor contribution to the amount of LDL cholesterol in the blood. COMA currently recommends that the current dietary intakes of between 300 and 400 mg/day should not rise. Restriction of dietary cholesterol (e.g., from eggs, shellfish) is advocated for those with particularly high levels because although dietary cholesterol is only moderately absorbed it seems to amplify the effects of saturates by restricting the liver clearance of LDL cholesterol. Fish oils (e.g., from mackerel, sardines, pilchards and salmon) may help reduce the tendency of blood to clot.
The Effect of Exercise
Even gentle exercise such as brisk walking has been shown to increase the HDL levels and reduce LDL levels and this effect is more marked with more intense exercise. These benefits have been shown particularly with aerobic exercise within the ACSM guidelines, but are probably also present within resistance training with medium resistance and high repetitions. In some people the total amount of cholesterol may remain the same, but HDL is, as we have seen, protective against CHD. So, combining a low cholesterol diet with regular exercise will lower significantly the risk of CHD
Is it really necessary to know blood cholesterol level? Knowing that you have a high cholesterol level may increase stress levels and since stress is itself a risk factor for CHD, it may be better to do everything possible to lower levels without actually knowing how high they are. People with a strong family history of very high cholesterol levels or of CHD (relatives suffering before 50 years of age) however should have cholesterol levels measured and lowered by drug therapy if necessary. The newer drugs available to doctors will lower very high cholesterol levels and reduce the risk of CHD.
PRACTICAL ADVICE TO DECREASE SATURATED FAT INTAKES:
- Major sources of SFA in the UK are meat products and dairy products. - Use semi-skimmed or skimmed milk in place of whole milk. - Use half fat cheese in place of regular cheese. - Buy lean cuts of meat. Trim the visible fat. - Choose cooking fats high in unsaturates, e.g. soya, corn, olive, rapeseed oils. - Use butter sparingly. - Avoid cream.
12 Tips to lower blood cholesterol levels
- Reduce intake of foods high in saturated fat
- Keep total fat intake low
- Eat more foods containing fibre
- Be regularly active
- Eat more beans and pulses
- Eat at least five portions of fruit and vegetables every day
- Choose vegetable oils for culinary purposes, e.g., olive, rapeseed, sunflower.
- Eat more complex carbohydrate foods, e.g., bread, rice, pasta, cereals and potatoes.
- Eat oily fish, e.g., sardines, herrings, mackerel, trout and salmon two to three times per week. - Avoid smoky areas and jogging along busy streets.
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