CHOLESTEROL DIETARY MANAGEMENT

Conventional Dietary Management of Cholesterol

While the development of plant sterol-enriched spreads is a very significant advance in the dietary management of cholesterol, it does not replace conventional dietary therapy. Rather, a plant sterol-enriched spread is an adjunct to conventional advice, which substantially increases the potential of diet to lower serum total and LDL-cholesterol.

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What is conventional diet therapy?

Since the 1960s dietary advice to lower blood cholesterol has revolved around the manipulation of dietary fatty acids. This advice was based on the work of two series of experiments conducted independently by Keys et al (1) and Hegsted et al (2). Both found saturated fatty acids raised blood cholesterol and polyunsaturated fatty acids lowered it. The potency of polyunsaturated fatty acids in lowering blood cholesterol was about half that of saturated fatty acids in raising it. Fats rich in monounsaturated fatty acids had a neutral effect on cholesterol. Dietary cholesterol was found to have a small, but significant, blood cholesterol-raising effect.

Based on these studies the key dietary advice for reducing cholesterol became the replacement of dietary saturated fat with polyunsaturated fat, with some reduction in dietary cholesterol. More recently, monounsaturated fats and carbohydrates have also been considered good substitutes for saturated fat, which remains the key dietary determinant of blood cholesterol.

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What are the main sources of saturated fat?

In western industrialised countries most sources of fat in the diet are rich in saturated fats. These include:
  • Dairy fats - butter, cheese, cream and full-fat dairy foods
  • Meat fat, sausages and luncheon meats
  • Baking fats used in commercial cakes, biscuits and pastries
  • Commercial frying fats used for takeaway foods and snack foods
The saturated fatty acid content of the fats in these foods is 50-60 per cent. Consumption of all these foods needs to be curtailed in order to reduce dietary saturated fat intake. Dairy fats are the most cholesterol-raising and special attention needs to be paid to reducing dairy fat in the diet. Low and reduced-fat milks and yoghurts are recommended.

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What are the main sources of unsaturated fats?

Margarine spreads and unsaturated vegetable oils are the only major source of fat in the diet not dominated by saturated fats. Polyunsaturated and monounsaturated fats comprise 75-90 per cent of fatty acids margarines and oils. These foods also serve as the major sources of the essential fatty acids, Vitamin E and Vitamin D in the diet.

The most freely available vegetable oils are sunflower, canola and olive oils. These are also used in margarine spreads. Although all three oils are recommended, sunflower and canola have an advantage over olive oil with respect to cholesterol-lowering. Advice for people is to:
  • Use table margarine instead of butter
  • Use sunflower, canola or olive oil in for frying and in salads
Nuts are also high in unsaturated fats and low in saturated fats. They may be recommended for people on cholesterol-lowering diets.

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Are trans fatty acids important?

Like saturated fats, trans fatty acids are cholesterol-raising. However, the trans fatty acid levels in the Australian and New Zealand diets are low. Virtually all high quality margarine spreads are now virtually free of trans fatty acids. The remaining sources of dietary trans fatty acids are dairy fat, meat fat and baking fats. As these are also major sources of saturated fat, advice to lower dietary saturated fats will also lower intake of trans fatty acids. No specific advice about trans fatty acids is recommended.

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Does total fat intake need to be restricted? No. Blood cholesterol levels are determined by the type of fat in the diet, not the total amount of fat. There is no need to restrict total fat intake. That said, if saturated fat is restricted in the diet, total fat intake will be limited as most sources of fat are rich in saturates. Most people who effectively restrict saturated fat and include margarines and oils in their diets end up with total fat intakes of approximately 30-32 per cent of energy i.e. relatively low.

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Are carbohydrates recommended?

Yes, blood cholesterol levels fall when dietary saturated fats are replaced by both starch and sugars. Recommended foods include:
  • Cereal foods such as bread, breakfast cereals, pasta and rice. Wholegrain versions are highly recommended.
  • All fruits, vegetables and legumes.
In moderation, sugar and sugary drinks are suitable for lean people. Some restriction of sugar may be considered for overweight people in order to limit calorie intake.

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Should dietary cholesterol be restricted?

The effect of dietary cholesterol on blood cholesterol is less than that of saturated fats and polyunsaturated fats. Also, there is considerable variation in response between individuals. In a sample of the general population, about 60-70 per cent will show little response to an increase in dietary cholesterol. The remaining cholesterol-sensitive individuals will show a significant increase in blood cholesterol.

As it is impossible to simply tell which people are sensitive to dietary cholesterol, it is prudent to advise all people with high blood cholesterol to limit dietary cholesterol. Advice to restrict saturated fat will assist in lowering dietary cholesterol. Further advice includes:
  • Restricting intake of eggs and offal meats.
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What does the Heart Foundation recommend?

The Heart Foundation recently made the following dietary recommendations for lowering blood cholesterol (3):
  • Use margarine spread instead of butter or dairy blends.
  • Use a variety of oils for cooking - some suitable choices include canola, sunflower, soybean, olive and peanut oils.
  • Use salad dressings and mayonnaise made from oils such as canola, sunflower, soybean and olive oils.
  • Choose low or reduced fat milk and yoghurt or 'added calcium' soy beverages. Try to limit cheese and ice cream to twice a week.
  • Have fish (any type of fresh or canned) at least twice a week.
  • Select lean meat (meat trimmed of fat and chicken without skin). Try to limit fatty meats including sausages and delicatessen meats such as salami.
  • Snack on plain, unsalted nuts and fresh fruit.
  • Incorporate dried peas (eg split peas), dried beans (e.g. haricot beans, kidney beans), canned beans (eg baked beans, three bean mix) or lentils into two meals a week.
  • Make vegetables, and grain based foods such as bread, pasta, noodles and rice the major part of each meal.
  • Try to limit take-away foods to once a week. Take-away foods include pastries, pies, pizza, hamburgers and creamy pasta dishes.
  • Try to limit snack foods such as potato crisps and corn crisps to once a week.
  • Try to limit cakes, pastries and chocolate or creamy biscuits to once a week.
  • Try to limit cholesterol-rich foods such as egg yolks and offal e.g. liver, kidney and brains.
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How effective is conventional dietary therapy?

In a meta-analysis of metabolic ward studies Clarke et al (4) found the replacement of 10 per cent of energy as saturated fats with a combination of polyunsaturated fats, monounsaturated fats and carbohydrate resulted in falls in total cholesterol of 10-15 per cent . Another meta-analysis of the effectiveness of dietary intervention in reducing blood cholesterol in studies with free-living humans found falls of about half this figure. The difference in results between the studies conducted in metabolic wards and the 'real world' are presumably due to problems with compliance (5). Nevertheless, a fall in cholesterol of 10 per cent following the introduction of conventional dietary therapy is realistic and achievable. When combined with a further 10 per cent fall through the use of a plant sterol-enriched spread, the potential fall in cholesterol with modern dietary therapy is of the order of 20 per cent.

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References
  1. Keys A, Anderson JT, Grande F. Prediction of blood cholesterol responses of man to changes in fats in the diet. Lancet 1957;2:959-966
  2. Hegsted DM, McGandy RB, Myers SM et al. Quantitative effects of dietary fat on blood cholesterol in man. Am J Clin Nutr 1965;14:776-787.
  3. Heart Foundation. Enjoy Healthy Eating: a guide to keeping your blood cholesterol in check. April 2002.
  4. Clarke R, Frost C, Collins R et al. Dietary lipids and blood cholesterol: quantitative meta-analysis. BMJ 1997;314:112-17.
  5. Tang JL, Armitage JM, Lancaster T et al. Systematic review of dietary intervention trials to lower blood cholesterol in free-living subjects. BMJ 1998;316:1213-19.
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