Dietary Cholesterol

Nearly all tissues of the body have the ability to produce cholesterol from saturated fat necessary for the formation of cell membranes and the synthesis of essential compounds such as bile acids and steroid hormones. As a consequence, there is no apparent need for cholesterol in the diet. There is no evidence of any beneficial effects of dietary cholesterol.

There is no epidemiological evidence that populations who eat a lot of cholesterol containing seafood/shellfish which are also high in moega-3 fats but low in saturated fat (e.g. prawns, squid, lobster, crab), have a high incidence of coronary heart disease (CHD).Quite the contrary. In parts of Asia (e.g. Japan) where the consumption of prawns and squid is amongst the highest in the world, CHD rates are low. Case control studies have not incriminated prawns, shrimp pastes (a concentrated source of cholesterol), squid or octopus or any other kind of seafood in heart disease and no clinical trial has ever shown them to be a problem.

Dietary cholesterol does influence the level of plasma cholesterol, although its effect is much less than that of the amount and the nature of dietary fatty acids. The relationship between cholesterol and the concentration of plasma cholesterol is not linear. For every additional 100mg of cholesterol consumed up to a total intake of 500mg per day, there is a 2-3% increase in the concentration of plasma cholesterol. In contrast further increases in cholesterol intake beyond 500mg per day have little additional effect on the plasma level (Hopkins AJCN 1992; 55: 1060-70). Over 50% of Australians have blood cholesterol levels above ideal - the Heart Foundation advises all Australians to be prudent and limit their cholesterol intake to <300mg/day.

Dietary cholesterol increases the concentration of both LDL and HDL cholesterol in most people, although the relative increase in the two fractions may vary markedly between people (Clifton et al. Arteriosclerosis 1990; 10: 394-401). A low fat diet and high cholesterol intake (600mg/day) from shrimps in normolipidaemic subjects raised LDL cholesterol by 7% but also raised HDL by 12% and decreased triglycerides by 13% - the LDL cholesterol to HDL cholesterol ratio dropped. In contrast, the low fat high egg diet (cholesterol intake 600mg/day) raised LDL by 10% and HDL by 8% (and increased the ratio of LDL to HDL). The authors (De Oliveira e Silva et al., AJCN 1996; 64: 712-7) conclude that moderate shrimp consumption in normolipidaemic subjects will not affect overall lipoprotein profile and can be included in ‘heart healthy’ guidelines.

It has been estimated that if cholesterol intake is greater than 500mg per day, a reduction in intake to 250mg per day will reduce the plasma total cholesterol by 5-7% which may be predicted to translate into a 10% reduction in the risk of CHD.

The evidence against seafood and eggs has come from confusion about cholesterol in food and cholesterol in the blood stream. The problem arose years ago when sections of the food industry decided the public would not be able to understand the fact that the body can make excess cholesterol when the diet is high in saturated fat. Instead of telling the public how much saturated fat foods contained, they chose to highlight cholesterol, tagging food labels with the words ‘no cholesterol’. To compound this absurdity, most of the foods that bore this claim had never contained cholesterol (e.g. olive oil) and many had high levels of saturated fat.

Eggs are casualties of this dogma. Combined with sausages or fried in butter and eaten with buttered toast, they can certainly contribute to high serum cholesterol levels, but it is the accompanying saturated fat that is the culprit. The main message to those with raised serum lipids should be to find alternatives to saturated fat. Take away fast foods have loads of saturated fat even if fried in ‘no cholesterol vegetable oil’ which is made from partially hydrogenated vegetable oils. This oil may not have cholesterol, but is high in saturated and trans fatty acids.

Prawns and seafood contain cholesterol, but the capacity of the liver to produce excess cholesterol, especially when the diet is high in saturated fat, far exceeds anything prawns or seafood can contribute. Also, some wrongly put oysters into the same category, although it is at least 30 years since we discovered that what had previously been assumed to be cholesterol in oysters was actually other sterols that turned out to be beneficial.

These examples show the importance of getting your message right from the start.

Unfortunately the early material from Departments of Health and the National Heart Foundation listed seafood/shellfish and eggs as foods to be avoided. 

Patients with elevated lipids can eat any seafood they like as long as it is not in batter or doused with butter and as long as the overall diet is low in saturated fat.

What about the new margarines which contain phytosterols, e.g. proactiv; do they lower blood cholesterol? One to two tablespoons/day of these margarines can lower blood cholesterol levels by up to 10% in three weeks when compared with a standard polyunsaturated spread. A CSIRO study this year (2000) used subjects aged 35-73 who were not on cholesterol-lowering medication or suffering from any diseases likely to affect blood cholesterol levels. They all had cholesterol levels >5mmol/l. However, some experts are expressing concerns about these margarines as they may encourage increased consumption of margarine under the “more is better” principal which could result in weight gain. There is no evidence to date suggesting that short-term consumption of plant sterols is unsafe, although long-term safety tests are yet to be performed. People with homozygous sitosterolaemia (a rare inherited metabolic disease) should restrict their intake of plant sterols; the gene frequency of those people who are heterozygotes is uncertain.

In summary

People at low risk of CHD can regularly eat cholesterol-rich foods (eggs, seafood and offal) as long as they keep saturated fat intake low.Unlike most eggs, ‘New Start Eggs' are also high in omega 3 fatty acids. Crayfish, lobster and prawns have a moderate - high cholesterol content (150mg/100g), but all other sea foods have a cholesterol content <100mg/100g and all seafood is low in saturated fat (as long as it not fried in animal or hydrogenated vegetable fat) and high in omega 3 fats.

People with a plasma cholesterol <5.0 mmol/l can eat seafood and one egg daily if they wish. For people with higher cholesterol levels, seafood and eggs can be consumed a few times per week if saturated fat intakes are low.

Last Updated: March 27, 2001.