Eggs

by Professor Wahlqvist & Dr Kouris-Blazos

For many decades, eggs have been perceived as somewhat unhealthy due to their cholesterol levels. Consumers assumed that the potential for ill-health coming from eggs was science based and it was in part.

For the last 5 years science has been re-testing old recommendations and beliefs about the limits for egg intake as well as testing the cholesterol message in relation not only to coronary heart disease, but also to general health and survival. Recent studies emphasize the large number of nutritional benefits one may accrue from regular egg consumption.

What's in eggs?

Eggs are a nutritional package of nutrients and other biochemical active components. They are nutrient dense, providing a wide variety of quality nutrients without having a high calorie content (about 70 calories per egg). The protein quality of eggs is high, providing all the essential amino acids needed for human protein synthesis and about 10% of the daily protein requirements (based on a 2000 calorie diet). However, nutrient composition of the eggs will depend on what hens eat. For example, a comparison between supermarket eggs and those that are free range have shown a 20-fold difference in omega 3 concentrations.

Egg protein is the standard against which other food proteins are measured. Eggs are good sources of vitamin A, B1, B12, D and E as well as folate, phosphorus, zinc and iron. Eggs are one of the rare natural sources of vitamin D. Macro and micronutrients aside, another area of interest for eggs is in their antioxidant content. In comparison to green leafy vegetables, eggs contain higher levels of the carotenoid antioxidants lutein and zeaxanthin. These two compounds are believed to be protective against age related macular degeneration, a condition that occurs in individuals older than 50 and which is the leading cause of blindness in the elderly.

Eggs contain around 250-300mg cholesterol per yolk. Expert bodies like the National Heart Foundation recommend an intake of cholesterol from all sources not exceeding 300mg per day. A slice of cheese (30g) or cup of full-fat milk has about 30mg of cholesterol; 100g cooked meat about 100mg and 100g fish about 50mg. Plant foods and their products (e.g vegetable oil) do not contain cholesterol.

Eggs and heart disease

Researchers from the Harvard School of Public Health who followed a large group of nurses (about 80,000) for 14 years found that there was no association between weekly egg consumption and coronary heart disease or stroke. These same investigtaors also examined this egg/cardiovascular disease relationship in more than 37,000 male health professionals followed for 8 years. Again there was not association between egg consumption and cardiovascular disease. Japan and France have low rates of death from heart disease compared with most other developed countries and both populations are high consumers of eggs.

(Reference: Hu FB, Stampfer MJ, Rimm EB et al. JAMA 1999; 281: 1387-1394)

Do eggs affect blood cholesterol levels?

Cholesterol from an egg can affect blood cholesterol levels in two ways. First, there are individual differences in the way people respond to certain foods. People who have high cholesterol levels are more likely to show a greater increase for the same amount of cholesterol in food than those whose blood cholesterol levels are initially lower. Secondly, different food habits or patterns can also influence the effect of egg consumption on blood cholesterol levels. Individuals who eat eggs and have a diet that is high in saturated fat (mainly from animal foods) are more likely to elevate their cholesterol levels than people who eat eggs and have a diet that's low in saturated fat. For example, bacon and egg on toast spread with butter is going to have a greater impact on blood cholesterol levels than an omelette consumed with salad. In other words, the saturated fat content of our diet has a greater impact on our cholesterol levels than the cholesterol content of our diet. This is because the absolute quantity of fat consumed in an average diet is much greater than the amount of cholesterol consumed and because saturated fat can be converted to cholesterol in the body.

So, if one has a high intake of saturated fats, derived mainly from animal fats (e.g butter, meat, dairy) as well as processed/commercial foods containing vegetable shortening/fat (e.g certain cakes, biscuits, sandwich spreads, fast food) their cholesterol levels may rise. In contrast, if one has an egg daily and a high intake of plant foods, but a low intake of animal fats and vegetable shortening (made by the super-hydrogenation of vegetable oil till it becomes more saturated and hard like butter) their cholesterol levels will most likely be within the acceptable range.

Eggs and diabetes

A study on over 1000 people with diabetes reported that a high intake of eggs and saturated fat were associated with a significant increase in mortality (Trichopoulos et al., J Intern Med. 2006 Jun;259(6):583-91). This finding is in agreement with other studies. For example, in 1999 Hu et el (JAMA. 1999 Apr 21;281(15):1387-94) reported that people with diabetes might have an increased risk of developing coronary heart disease (CHD) or stroke if they eat one or more eggs per day. For the study, 37,851 men and 80,082 women were observed as part of the Health Professionals follow-up study (1986 to 1994) and the Nurses' Health Study (1980 to 1994). Participants eating more than one egg per day were unlikely to develop coronary heart disease (CHD) or stroke, except in the subgroup of people with diabetes. Researchers suggest that the apparent increased risk of CHD and stroke associated with higher egg consumption among participants with diabetes warrants further research.
Read more about eggs

How many eggs a week? Around 4 small eggs per week is great. For example, try to have at least one egg meal a week such as omelette or spinach/ricotta/egg parcels or vegetarian lasagna containing boiled eggs. If you have a cholesterol level less than 5mmol/l and if you have a low intake of animal fats you can have 1-2 eggs daily if you wish. If your cholesterol level is >7mmol/l or if you have diabetes or other heart disease risk factors (like hypertension or smoking) it is advisable to limit intake to 1-2 a week. Also, remember that eggs are a 'meat alternative' - this means that when you have an egg meal it counts as a 'serving of red meat' - which is great news for vegetarians.

From a social aspect, eggs have a wide cultural acceptance, being used in cooking worldwide. They are convenient and a benchmark indicator of whether one has the ability to cook. Additionally they are consumed by every generation from childhood to later life and given their nutrient density are especially valuable for the elderly, as energy expenditure and intake decline. Yet it is older people who have, in developed countries, been reluctant to eat eggs because of concerns about heart disease. In their own way, eggs are an affordable functional food, serving a purpose for everyone and every culture.

See also the HEC healthy eating pyramid.

See also "Food Questions and Answers" for more information on eggs.

Last Updated: June, 2006