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How dietary measures can help reduce unhealthy blood cholesterol levels

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Kathy Cowbrough

Consultant Dietitian and Public Health Nutritionist, Retford, Nottinghamshire

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Despite the decline in the incidence of coronary heart disease (CHD) in the UK population since the 1970s, this country still has one of the highest incidence rates in the world. The risk of CHD is directly related to blood cholesterol levels. The National Heart Forum (2002) estimated that 45% of deaths from CHD in men and 47% of deaths in women are due to raised blood cholesterol (in this case more than 5.2mmol/L).

When blood cholesterol rises from 5mmol/L to 7.8mmol/L, the age-adjusted six-year death rate is three times higher than at 5mmol/L (University of Leeds, 1993). However, cholesterol levels must not be interpreted on the basis of their numerical value alone but always in the context of overall cardiovascular disease risk. Cholesterol is one of a number of independent risk factors. Overall risk is determined by a combination of factors, including age, gender, family history of heart disease, and whether a person smokes, is overweight, has high blood pressure or diabetes.

Different guidelines may give slightly different advice for managing high levels of blood cholesterol (hyperlipidaemia) (see Policy box). The Joint British Society Guidelines (Wood et al, 1998; British Cardiac Society et al, 2000; see Box 1) recommend that, for certain patient groups, along with lifestyle and blood pressure control, the total cholesterol level should be no higher than 5mmol/L and the LDL cholesterol should be below 3mmol/L. These patients include those:

- With established coronary heart disease

- With other major atherosclerotic disease

- With hypertension, dyslipidaemias, diabetes, family history of premature CHD, or a combination of these risk factors, which puts them at high risk of developing CHD or other atherosclerotic disease.

The National Service Framework for Coronary Heart Disease (DH, 2000) suggests a cholesterol target of less than 5.0mmol/L for both primary and secondary prevention. The higher the risk of heart disease (for example, a male smoker with high blood pressure and diabetes), the greater the need to reduce cholesterol levels. Taking a lipid profile of high-risk individuals can help to identify more specific treatment for each person.

Cholesterol metabolism
Cholesterol is a wax-like substance that belongs to the lipid family. It can be produced naturally by animals and humans and is vital to normal body functioning. It is a primary component of cell membranes and is a substrate (or precursor) for the synthesis of bile acids that assist with fat digestion, the production of steroid hormones (sex hormones, for example), and vitamin D.

It is a myth that eating foods containing cholesterol causes high blood cholesterol. Research shows that it is the fat in food, particularly saturated and trans fats, and not the cholesterol that has the greatest effect on raising blood cholesterol (DH, 1994).

Trans fats occur as the result of hydrogenation, which is the industrial process of hardening oils used in the manufacture of margarine, spreads, biscuits, cakes and other products. Because these fats act in the body in the same way as saturated fat, they can increase blood cholesterol. Current guidelines are that the intake of trans fats should not be greater than 4-6g/day (Thomas, 1996). Dietary cholesterol is found in animal foods such as meat, fish, poultry, eggs and milk products. Although it does not normally affect blood cholesterol, a small percentage of people with a family history of high blood cholesterol levels are very sensitive to it and therefore must limit it in their diet.

The majority of cholesterol found circulating around the body is produced by the liver, which it converts from saturated fat. When too much cholesterol is produced, it builds up inside blood vessels (atherosclerosis), even- tually blocking them and causing vascular diseases such as heart disease, strokes and peripheral vacsular disease.

Cholesterol is transported through the blood as part of a complex particle called lipoproteins. There are two main types of x lipoproteins, each with a different function:

- Low-density lipoproteins (LDL) carry cholesterol to the body's cells

- High-density lipoproteins (HDL) help clear excess cholesterol from the arteries and carry it back to the liver to be destroyed.

The amount and type of cholesterol in the blood can increase the risk of coronary heart disease and disease of arteries elsewhere in the body. Thus, excess LDL cholesterol contributes to the development of CHD by increasing the rate at which cholesterol is deposited in damaged arteries, ultimately causing the development of plaque and narrowing of the arteries.

High levels of HDL cholesterol suggest a reduced risk of CHD, as HDLs remove excess cholesterol from tissue. On the other hand, high levels of LDL and low levels of HDL indicate more risk of heart disease, while high levels of triglycerides and a low level of HDL increase the risk of CHD.

Ways to reduce cholesterol levels
Factors predisposing towards unhealthy cholesterol levels include:

- Eating a diet high in saturated (animal) fats and/or trans fats found in processed foods

- Being overweight

- Lack of physical activity.

The following guidelines are a means of controlling blood cholesterol levels.

Eat well - A healthy eating pattern that is low in saturated and trans fats can lower LDL cholesterol. A diet high in manufactured foods may be high in trans fats, although many manufacturers of margarines and spreads have reduced trans fats in their products to extremely low levels. Many foods containing trans fats also contain saturates, so any dietary change to reduce saturates is likely to reduce trans fats. For information on the variety of foods from each food group that should be eaten daily see www.food.gov.uk

Keep weight under control - Being overweight, particularly having excess weight around the waist, is linked to higher LDL cholesterol levels (Hans et al, 1995; British Dietetic Association, 2002). Table 1 shows the waist measurements for European and Asian men and women that suggest they are at higher risk of high LDL cholesterol levels.

Be active - Physical activity can increase HDL cholesterol. Adults should have at least 30 minutes a day of moderately intense physical activity on five or more days of each week (DH, 2004).

Dietary change
There is evidence (DH, 2004; Scottish Intercollegiate Guidelines Network, 1999) that dietary change can help lower blood cholesterol levels, although the reported effect is variable, depending on the restrictions in the diet and the amount the blood cholesterol is raised. Cholesterol-lowering, however, is only one of a range of possible effective interventions to reduce the risk of CHD. Dietary changes have potential benefits in addition to cholesterol-lowering; for example, protection against weight gain, high blood pressure, and diabetes.

It has also been shown (Hooper, 2004) that non-cholesterol-lowering diets reduce CHD risk significantly. For example, an increase in oily fish has been shown to reduce cardiovascular mortality after heart attack without reducing cholesterol levels. Hooper et al (2004) reported significant reductions in CHD in a trial of a Mediterranean diet in people after myocardial infarction, but there was no effect on cholesterol levels.

It is important to assess the most important changes that an individual should make and to be aware that only small changes may be able to be made at a time. But even small changes can mean big benefits.

Dietary recommendations
Avoid saturated fats - These can be found in a range of foods, including the following:

- Butter, ghee, lard, hard hydrogenated margarines, coconut or palm oil or some blended vegetable oils

- Full-fat dairy foods, including full-fat milk, hard cheese, full-fat yoghurt, cream

- Fatty cuts of meat: lamb, beef, pork, meat products (sausages, burgers, pies, cooked meats, luncheon meats)

- Hidden sources: biscuits, cakes, pastries, confectionery, savoury snacks.

Replace saturated fats - These should be replaced with fats high in mono-unsaturated fatty acids, such as olive oil, rapeseed oil and fats high in polyunsaturated fatty acids (n-6 PUFA) found in sunflower oil, and corn oil with an upper limit of 10% of dietary energy from n-6 PUFA.

Soluble fibre - Include soluble fibre in recipes or in meals; for example, pulses (lentils and beans), oats and fruit and vegetables. Soluble fibre has been shown to lower plasma LDL cholesterol to varying degrees (DH, 1994). The higher the initial level of cholesterol, the greater the cholesterol-lowering effect.

Reduce dietary cholesterol - Dietary cholesterol has to be reduced to extremely low levels before it has any significant effect on blood cholesterol levels. Within the range of normal intake (250-400mg cholesterol/day), the effect of dietary cholesterol on blood cholesterol is very small. People with familial hypercholesterolaemia may be advised to lower dietary cholesterol below 300mg (Thomas, 1996). This will mean avoiding most animal products (see www.food.gov.uk).

Eat soya protein - The Joint Health Claims Initiative (www.jhci.co.uk) has been presented with enough evidence for them to allow the following health claim to appear on labels if appropriate: 'The inclusion of a least 25g of soya protein per day as part of a diet low in saturated fat and cholesterol, can help reduce blood cholesterol levels.'

Eat products designed to lower cholesterol - There is evidence that certain foods containing added ingredients such as plant sterols and stanols can reduce levels of cholesterol in the blood. These substances are found in specially developed products, such as some spreads and yoghurts. They cost more than their normal equivalents, but they can help to cut cholesterol levels when used as part of a healthy diet. However, people who do not have high cholesterol levels should not eat these products regularly, particularly children and pregnant or breastfeeding women (www.food.gov.uk) (DH, 1994).

Alcohol intake - Drink alcohol in moderation - the recommendation regarding alcohol is controversial and has to be balanced against the risk and benefit of alcohol to health. Light or moderate alcohol intake (one to two units a day) appears to increase HDL cholesterol. However, alcohol should be avoided in those with raised triglyceride levels (DH, 1994).

Garlic - There are some claims that including garlic in the diet reduces LDL cholesterol and increases HDL cholesterol but the evidence is limited and inconclusive (DH, 1994).

Conclusion
CHD remains a major cause of premature death and imposes high personal, social and economic costs. Blood cholesterol is an important risk factor for CHD but should be considered in the context of other risk factors such as smoking, raised blood pressure and physical inactivity. Thus blood cholesterol alone is a relatively poor predictor of individual CHD risk so intervention and treatment should reflect the overall risk and be tailored according to an individual's lifestyle. (NHS CRD, 1998).

Latest policy
- The National Service Framework for Coronary Heart Disease in clinical practice suggests a cholesterol target of less than 5.0mmol/L in both primary and secondary care settings (Department of Health, 2000)

- The World Heart and Stroke Association claims that, although goals for total cholesterol and low-density lipoproteins cholesterol have been set, there is insufficient evidence to justify goals for triglycerides and HDL cholesterol. Instead, these measurements should be used to identify individuals at high multifactorial risk of coronary heart disease or other atherosclerotic disease and possibly used as secondary considerations in the selection of lifestyle and drug interventions (Smith et al, 2004).

Key points
- The risk of coronary heart disease is directly related to blood cholesterol levels

- Reducing blood cholesterol to below 5.0mmol/L can significantly reduce the incidence of heart attack or other coronary events (DH, 2000)

- Blood cholesterol levels can be reduced by dietary changes, particularly a reduction in the consumption of saturated fats

- People with diabetes, in particular those with Type 2 diabetes, have a greater incidence of CHD.

Author's contact details
Kathy Cowbrough, Consultant Dietitian, PHN, The Cottage, Little Gringley, Retford, Nottinghamshire DN22 0DU. Email: kathy.cowbrough@virgin.net

Useful websites for health professionals
Clinical Evidencewww.clinicalevidence.orgSections on acute myocardial infarction and secondary prevention of ischaemic events.

Scottish Intercollegiate Guidelines Networkwww.sign.ac.ukGuideline No 41: Secondary Prevention of CHD Following Myocardial Infarction. Guideline No 57: Cardiac Rehabilitation.

National Institute for Clinical Excellencewww.nice.org.ukClinical guideline: Prophylaxis for Patients Who Have Experienced a MI (April 2001)

British Heart Foundationwww.bhf.org.ukStatistics on coronary heart disease

Heart UKwww.heartuk.org.uk/Useful factsheets, including one on cholesterol.

British Dietetic Association. (2002) Food First Weight Wise Campaign Guide. London: British Dietetic Association.

British Cardiac Society, British Hyperlipidaemia Association, British Hypertension Society, British Diabetic Association. (2000)Joint British recommendations on prevention of coronary heart disease in practice: summary. British Medical Journal 320: 705-708.

Department of Health. (1994)Nutritional Aspects of Cardiovascular Disease. Report of the COMA Cardiovascular Review Group. Report on Health and Social Subjects, No 46. London: Stationery Office.

Department of Health. (2000)National Service Framework for Coronary Heart Disease. London: DH.

Department of Health. (2004)At Least Five a Week: Evidence on the impact of physical activity and its relationship to health. A report from the Chief Medical Officer. London: Department of Health.

Hans, T.S., Van Leer, E.M., Seidell, J.C., Lean, M.E.J. (1995)Waist circumference action levels in identification of cardiovascular risk factors. British Medical Journal 311: 1401-1405.

Hooper, L., Griffiths, E., Abrahams, B. et al. (2004)Dietetic guidelines: diet in secondary prevention of cardiovascular disease (first update June 2003). Journal of Human Nutrition and Dietetics 17: 337-349.

NHS Centre for Reviews and Dissemination. (1998)Cholesterol and Coronary Heart Disease: Screening and treatment. York: Centre for Reviews and Dissemination, University of York.

National Heart Forum. (2002)Coronary Heart Disease: Estimating the impact of changes in high- risk factors. London: The Stationery Office.

Scottish Intercollegiate Guidelines Network. (1999)Lipids and the Primary Prevention of Coronary Heart Disease. SIGN Publication No 40. Edinburgh: SIGN.

Smith, C., Jackson, R., Pearson, T.A. et al. (2004)Principles for national and regional guidelines on cardiovascular disease prevention - a scientific statement from the World Heart and Stroke Forum. Circulation 109: 3112-3121.

Thomas, B. (1996)Nutrition in Primary Care. A handbook for health professionals. Oxford: Blackwell Science.

University of Leeds. (1993)Effectiveness Review: Cholesterol - screening and treatment. Available at: www.jr2.ox.ac.uk/bandolier/band5/b5-2.html (accessed on November 5, 2004)

Wood, D., Durrington, P., McInnes, G. et al. (1998)Joint British recommendation on prevention of coronary heart disease in clinical practice. Heart 80: (suppl 2): s1-s29.

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