Good Eggs and Bad Eggs
Are You Going to Work on an Egg?
It is more than 20 years since Edwina Currie upset UK retailers by claiming that the food poisoning bug Salmonella enterica was widespread in British eggs. Established microbiological research suggests that it is the chicken rather than the egg, which carries the greatest incidence of the bacterium - and you can usually cook your way out of trouble if you observe strict kitchen hygiene and read the instructions carefully.
The Great Cholesterol Debate
The focus has now moved to the amount of dietary cholesterol inside an egg, which along with prawns, liver and kidney is surprisingly high at over 250mg per 100g portion (1). Recent research from the British Nutrition Foundation suggests that eggs are not the health hazard nutritionists once feared (2). In the mid-1960s, Britons consumed an average of five eggs per week, falling to fewer than two per week in the mid-1990s. In 2007 the British Heart Foundation quietly lifted its warning not to consume more than three eggs per week. So why the change in heart?
The Chemistry Behind the News
Cholesterol is an essential metabolite for the body, assisting in the production of several steroid based hormones as well as vitamin D synthesis and cell membranes structure. Our body gains only about 25% of its cholesterol from food and manufactures the rest within the liver, using other fats digested and absorbed from the diet. It has a different chemistry to the saturated animal fats linked to coronary heart disease (3). However, too much fat on our plates leaves spare cholesterol molecules wandering round the blood stream - causing problems inside our arteries. It is important to consume enough fat to cover our daily needs - about 75g per day for adults, the majority of which should be unsaturated fats derived from vegetable oils. This equates to approx 5 tablespoons of olive oil or 120g low fat margarine per day. This is easily achieved when one remembers the fat content of biscuits, cake, chocolates and hot buttered toast!
The Biology of Eggs
There are no significant differences in the nutritional composition of eggs obtained from battery, deep litter or free range eggs, although organically farmed eggs may have a different mineral profile and hens fed an omega-3 oil supplemented diet produce correspondingly enriched yolks. Adding greenstuffs to the feed, or adding natural and synthetic pigments can result in stronger yolk colours from battery hens. The shell colour depends more on the breed of hen rather than the nutrient content (4).
Although a large egg contains approx 1.5mg of iron, most of this is not available for absorption due to binding of the iron atoms to phosphate and protein molecules. Eggs contain no carbohydrates or vitamin C, but otherwise provide everything that a developing chick embryo needs to survive beneath its porous calcium carbonate shell (1). Vegetarian diets which exclude dairy products need careful planning to redress the shortfall otherwise filled by one of nature's most nutrient dense foods.
A Timely Reminder
A diet lacking eggs is nothing new. They were banned during the period of Lent as early as the ninth century, which spawned the concept of Easter Eggs, although the chocolate version arrived a little later, with a more tempting nutritional profile! Nevertheless, in any shape or form they remain a powerful symbol of fertility and new life, given in friendship and love with the welcoming warmth of Spring (5).
Who will get your egg this year?
References:
- Lean M. (2006) Food Science, Nutrition and Health. Arnold.
- Gray J. Griffin B. (March 2009) Eggs & dietary cholesterol - dispelling the myth. Nutrition Bulletin Vol 34, (1) British Nutrition Foundation.
- Enig M.G. (2000) Know Your Fats. Bethesda Press, Maryland.
- Food Standards Agency (2008) Manual of Nutrition. London TSO.
- Egg Farmers of Canada (2009) A Brief History of Eggs.
Life on a Plate?
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