Wednesday February 11 2009
Eggs are a good source of protein, vitamins and minerals
“Going to work on an egg may be good for you after all” reported The Times. Widespread media coverage was given to new research that challenges the idea that eating one egg a day will lead to high cholesterol and heart disease. The newspaper reported that nearly half of British people wrongly believe that three eggs a week is the most that should be eaten.
The story is based on a review that claimed the cholesterol in eggs has only a small and clinically insignificant effect on blood cholesterol. The authors mention the benefits of eating eggs and say that it is time to “restore eggs to their rightful place on our menus”.
This research does not describe its methods and so it is not possible to carry out a full appraisal of its quality. However, it is likely that the original research, which advised limiting egg consumption, was faulty. This review, while not presenting new knowledge, does promote the health benefits of eggs and goes some way to dispel the myth about the harm they cause. The FSA already lists eggs as a good source of protein, vitamins and minerals. It also states that, despite eggs being high in cholesterol, the cholesterol they contain is not as harmful as saturated fat from meat.
Where did the story come from?
Dr Juliet Gray, a registered public health nutritionist from Guildford, and Dr Bruce Griffin, from the University of Surrey, co-wrote this study. They are both independent advisors to the British Egg Industry Council. No sources of funding are declared in the publication, but The Times reports that there was some funding from the egg industry. The study was published in the (peer-reviewed) journal of the British Nutrition Foundation the Nutrition Bulletin.
What kind of scientific study was this?
The aim of this narrative review, “Eggs and dietary cholesterol − dispelling the myth”, was to give an overview of the evidence on egg consumption and its perceived risks. The authors state that there is a popular misconception that eggs are “bad for your blood cholesterol” and therefore “bad for your heart”. They say this myth persists among many people, and influences the advice of some health professionals.
The authors explain that the cholesterol found in eggs has only a small and clinically insignificant effect on blood cholesterol especially when compared with the much greater and more harmful effects of saturated fatty acids found in foods such as red meat and butter. Because of this, the recommendations from major food and health bodies concerning dietary cholesterol have been relaxed in the UK and elsewhere in recent years. They go on to review over 35 studies that support this.
The authors say the myth originally came about in the US in the 1970s and was due to a misunderstanding of how dietary cholesterol affects blood cholesterol. They say that animal studies in which large amounts of butter were fed to rats and rabbits caused the mistaken belief that cholesterol in the diet converts directly into blood cholesterol. They say this may be because the narrowing of arteries that causes heart disease is due to cholesterol-rich deposits. It was thought that dietary cholesterol must, therefore, be a central cause of heart disease in both animals and humans.
However, since then, the authors say, data from better designed studies have established an “indisputable link” between raised LDL-cholesterol (the sort that is increased by eating meat products containing saturated fats) and an increased risk of coronary heart disease. The overall effect of dietary cholesterol is small and clinically insignificant in comparison with the established LDL-raising effects of saturated fatty acids. They also explain that many of the original studies did not consider the effects of saturated fat in the diet. The increased risk thought to be caused by eating eggs may have been caused by eating meat, as eggs are often accompanied by meat.
They then describe the nutrient composition of eggs as reported by the Food Standards Authority (FSA).
Part of the review describes the changing recommendations concerning egg intake. The authors say that US health agencies have made more stringent recommendations concerning egg consumption than the UK. From the 1960s onwards, people in the US with strong family histories of high cholesterol were put on cholesterol-lowering diets and advised to limit their egg intake. From 1970, all US consumers were warned about egg consumption. In 2000, The American Heart Association removed specific references to eggs in their dietary recommendations for heart health, but maintained that people should restrict their cholesterol intake to under 300mg per day.
The authors quote 2008 advice from the British Heart Foundation, which shifts the emphasis to reducing saturated fats in the diet. They emphasise that dietary sources of cholesterol, such as eggs, offal and seafood (for example prawns), do not usually contribute greatly to circulating cholesterol levels.
What were the results of the study?
The FSA reported in 2002 that eggs are high in cholesterol (approximately 225mg in a medium-sized egg). However, the total fat and saturated fatty acid content is not high, and the fat in eggs is predominantly unsaturated (44% monounsaturated; 11% polyunsaturated).
The FSA also reported that an egg is relatively low in energy (approximately 335 kJ/80 kcal in a medium-sized egg) and that it is a valuable source of many essential micronutrients and a rich source of high-quality protein.
The authors also say that the British Heart Foundation no longer suggests a limit on the number of eggs consumed, and the charity uses eggs in recipes that encourage a healthy approach to eating and weight control.
What interpretations did the researchers draw from these results?
The authors say there is now “no doubt that a raised concentration of serum LDL-cholesterol increases the risk of coronary heart disease”. They say that the previous evidence showing a link between dietary cholesterol intake and raised serum LDL-cholesterol was confounded by the presence of saturated fatty acids in the experimental diets. The overall effect of dietary cholesterol is small and clinically insignificant in comparison with the established LDL-raising effects of saturated fatty acids.
They say that eggs are a cheap, nutrient-dense food, a valuable source of high quality protein and essential micronutrients that is not high in saturated fats or in energy. They conclude that it is “high time that we dispelled the mythology surrounding eggs and heart disease and restored them to their rightful place on our menus where they can make a valuable contribution to healthy balanced diets.”
What does the NHS Knowledge Service make of this study?
This narrative review summarises the current state of knowledge about eggs and presents a view of the evidence supporting the idea that eggs are not as bad as once thought. These facts may be correct, however the review was not systematic and there are some concerns about the methods the authors used:
- This is a narrative review and did not include a description of the methods that were used. It is, therefore, not possible to be sure that the research took into account all relevant research, both positive and negative.
- The criteria for selecting and assessing the quality of the individual studies that were included are not reported. This means that the reader cannot judge the evidence themself, but must rely on the authors’ judgements about the reliability and relevance of these studies.
As this research does not describe its methods, it is not possible to carry out a full appraisal of its quality. A systematic review would be needed to better establish egg safety. However, it is highly likely that the original research which advised limiting egg consumption was faulty. The conclusions of this review are not new knowledge, but do promote the health benefits of eggs and dispel the myths about the harm they cause.
The FSA already lists eggs as a good source of protein, vitamins and minerals. It says that, despite being high in cholesterol, the cholesterol found in eggs is not as harmful as saturated fat from meat.