29 August 2012 Last updated at 10:08

Why are eggs now better for us?

By Michelle Warwicker BBC Food

British eggs are more nutritious now than they were 30 years ago, research shows. But why?

Whether fried in a traditional English breakfast, whipped up in an omelette or used as an ingredient in countless cake recipes, eggs are one of the most versatile of foods and form a staple part of many diets.

British eggs now contain 75% more vitamin D, 20% less fat and double the amount of the mineral selenium compared to those in the 1980s, when the last government analysis was carried out, a study led by the Institute of Food Research has found.

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The amount of cholesterol in a whole egg has also decreased overall, although the level of cholesterol has increased in egg yolks.

"Overall I think it's a positive sign that the composition is certainly nutritionally better," says the Institute of Food Research's Paul Finglas, who led the research.

"Anything that can contribute to increasing selenium intakes from food that we consume is a good thing."

Deficiency in the mineral is associated with increased risk of cancer, cardiovascular disease, and infertility, but in the UK "we are sort of low on selenium in the diet", he explains.

One key reason for our improved eggs is the changes made to hens' feed since the 1980s, explains Amanda Cryer, director of the British Egg Information Service.

When eggs were last analysed, meat and bone-meal products were included in chicken feed. But the BSE scare in the 1990s meant that the meat products were removed and "replaced by vegetable oil".

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The use of enzymes in hens' feed to improve the birds' health has also had a positive "knock-on effect into the egg".

Fans of eggs today demand larger-sized eggs than consumers in the 1980s did.

As eggs get larger, the amount of white in the egg increases more than the amount of yolk, so the white-yolk ratio changes with the size of the egg.

So although the amount of cholesterol in yolk alone has increased, the study concludes that if eggs are taken as a whole, with the white included, cholesterol has actually gone down by 10%.

Improvements in analysis methods since the 1980s could mean that researchers are only now picking up on some of the nutritional benefits that may have already existed in eggs.

"For example... there may always have been more vitamin D in eggs than was thought, but it wasn't picked up as much," says Ms Cryer.

What's in an egg?

Nutrients	Average large egg in the 80s	Average large egg in 2011
Energy kcal	91	77
Protein g	7.6	7.5
Total fat g	6.8	5.3
Saturated fatty acid g	1.9	1.5
Cholesterol mg	237	207
Vitamin D mcg	1.1	1.9
Selenium mcg	7	14

Source: British Egg Information Service

But she maintains that there is "no doubt" that eggs today show a "significant increase" in vitamin D compared with those people were eating 30 years ago.

According to the British Egg Information Service, 32 million eggs were eaten per day in the UK in 2011, with the retail market value estimated to be £885m.

And the UK egg industry has seen an increase in consumption in recent years.

Ms Cryer believes that the "critical point" in the British egg revival came when the British Heart Foundation removed its previous advice to limit eggs to three days a week, after research showed that cholesterol in foods such as eggs did not directly increase blood cholesterol.

However a new study from Western University in Canada links egg yolks with the "increased build-up of carotid plaque" - a "risk factor for stroke and heart attack".

People "eating three or more yolks a week had significantly more plaque area than those who ate two or fewer yolks per week", the study also suggests.

But the British Egg Information Service disputes this study, saying that researchers "did not take into account other lifestyle factors that will impact on cholesterol such as; saturated fat intake, alcohol intake, exercise".

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Under World War II rationing, eggs were a rare treat.

The British Egg Marketing Board used "egg chicks" to promote eggs in 1966

See how dried eggs were rationed and used in WWII cooking

Tightly rationed until 1953, British eggs entered into their heyday in the 50s and 60s with advertising campaigns such as the famous "Go to work on an egg" television advert in 1957, starring comedian Tony Hancock.

The UK population celebrated the return of the egg and in the 1960s, egg consumption reached its peak at nearly five eggs per person per week.

"We're eating more now than we were in the 80s. We're not eating more than we were in the 50s and 60s though," says Amanda Cryer.

But this association with post-war 1950s and 60s cuisine could mean that eggs are seen as "old-fashioned" by some of today's cooking fans.

"They probably are seen as a bit of an old-fashioned product," says Emily Davenport, who compiled the cookbook "Take a box of eggs", featuring 100 recipes using eggs.

The cookbook is the latest annual recipe collection published by the Dairy Diary company - which sells most of its books via door-to-door milkmen.

How hens have fared:

• In the 80s something like 90% of laying hens were kept in cages. These days in the UK it's 50% cage and 50% free range.
• A law banned battery cages from 1 January 2012 and says that if hens are kept in cages in the UK they must be larger, "enriched cages".
• Eggs contain the same nutritional values same across all production methods because the feed usually remains the same whether hens are caged or free range.

Source: Amanda Cryer, director of the British Egg Information Service

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And Ms Davenport admits that when she first started to compile the recipes, it was the "obvious "and "quite old-fashioned" egg recipes she thought of, like "egg custard and that sort of thing."

She says that some of her favourite recipes are some of the more modern and "exciting" takes on traditional recipes such as omelettes.

"I've always in the past done bog-standard cheese or mushroom omelettes.

"But just chucking a few sweet potatoes in or a bit of brie and a few herbs - things that you've got in the cupboard or in the fridge.

"Things that you can go home and do really quickly - but are far more tasty and interesting to the omelettes that my mum used to cook."