Nutrition: So should you really be going to work on an egg?
Science has long been divided over whether eggs are good for us — or dangerously high in cholesterol. We unscramble facts from fiction...
GO TO work on an egg – unless you’re worried about heart disease, that is. As slogans go, this qualifier somewhat spoils the original 50s Egg Marketing Board advertising campaign. By the 70s, health authorities were advising the public to avoid eggs, as the cholesterol they contain might contribute to heart disease.
These days the message about whether eggs are good or bad for us is decidedly scrambled.
"There’s a lot of confusion around eggs," says consultant dietitian Sian Porter. "On the one hand, they’ve had a bit of a renaissance with the trend for high-protein diets. But at the same time, people with raised cholesterol, in particular, have concerns about whether they can safely eat them."
There is a steady stream of apparently conflicting evidence from scientific studies. Higher consumption of eggs was linked to a higher risk of heart disease and early death in a major US study of nearly 30,000 adults, published in the journal JAMA earlier this year.
Yet less than a year earlier, in 2018, another major study – based on data from half a million adults and published in the journal Heart – found that moderate egg consumption was associated with a lower risk of heart disease.
So what’s going on?
"Historically, we assumed that eggs, along with other foods that contain cholesterol [such as red meat and prawns], would raise the cholesterol in our blood," says Rosie Saunt, a dietitian and co-author of Is Butter A Carb? Unpicking Fact From Fiction In The World Of Nutrition. And there is a clear link between high cholesterol and a risk of heart disease, which is why the advice used to be to limit egg consumption.
"But then, as the science evolved, we found out that eating dietary cholesterol doesn’t actually significantly raise the amounts of cholesterol in our blood at all – so now there is no upper limit suggested for egg consumption in the UK."
Instead, when it comes to high cholesterol, factors such as smoking, eating too much saturated fat and not exercising are believed to be much more important. Some people may also be more susceptible because of their genes rather than lifestyle.
While no one is recommending taking it to extremes, à la Margaret Thatcher’s power diet of 28 eggs a week, or Charles Saatchi, who reportedly lost 4st by eating nine eggs a day, "we can confidently say that eggs are a safe and healthy contribution to our diets’, emphasises Rosie Saunt, who herself eats "about an egg a day" on average.
In fact, all the experts Good Health spoke to for this article say they eat eggs regularly.
TRUTH BEHIND EGGS’ BAD PRESS
The reason eggs so often get linked with frightening health effects seems to be that many of these studies are observational, which means the effects of eating a particular food aren’t tested directly. Instead, participants complete questionnaires about their diets and are then tracked for particular health conditions.
"While this most recent piece of research [the JAMA study] was quite a large, well-designed study, the dietary information was based on people self-reporting what they ate, once, before they were followed up for outcomes 17 years later," explains Rosie Saunt.
"It can show an association between eggs and an increased risk of heart disease, but it can’t show definitive cause and effect."
Dr Scott Harding, an assistant professor of nutritional biochemistry at Memorial University of Newfoundland, Canada, adds: "What often happens with studies like this is that certain foods associate with disease. But those foods also associate with whole dietary patterns, so people who eat a lot of them also consume too much food in general, or are sedentary."
Indeed, as Tom Sanders, an emeritus professor of nutrition and dietetics at King’s College London (and a fan of egg-and-cress sandwiches), explains, there’s a strong correlation between egg intake and unhealthy lifestyles.
"For example, in the US, eggs are often eaten with bacon, sausages or burgers, so it’s impossible to disentangle the effects on the risk of cardiovascular disease of eggs from these fatty meat products," says Prof Sanders.
"With this sort of study, you also don’t tend to know how people have cooked their eggs," adds Sian Porter (who has eggs around three times a week). "There’s a big difference between someone who regularly has fried eggs with bacon and one who has healthier options, such as boiled eggs with rye bread."
Rosie Saunt adds: "When we look at intervention studies – higher-quality studies, where they get people to eat eggs and measure what happens to their blood – eggs seem to raise 'good' HDL cholesterol, the kind that we want, not the 'bad' LDL cholesterol associated with heart-disease risk."
CHOLESTEROL ISN’T ALL BAD
According to Dr Harding, whose research focuses on dietary fats and their link with heart disease: "Cholesterol gets a really bad name but it’s absolutely essential for us to survive."
Indeed, cholesterol is a fatty substance we get from animal products – but our bodies can also make it if needed. We use cholesterol to produce certain hormones, the membranes that protect our cells and also to make bile, which helps digestion.
"This means your body is constantly trying to balance its levels of cholesterol, depending on how much is coming in," explains Dr Harding. "A healthy person has no problem tightly regulating their cholesterol at a certain level."
It’s when something goes wrong with this regulation process that problems show up in the form of raised cholesterol in the blood.
"The tissues push excess cholesterol into the blood when they’ve got enough, so other parts of the body can use it," says Dr Harding. "But if they don’t need it either, it stays parcelled up in particles called low-density lipoproteins [that’s the 'bad’ LDL].
"This is the last resort place to store cholesterol. But blood vessels are not designed for that, and so it starts to cause damage, which is why it’s associated with heart disease."
Yet it’s not as simple as saying that too much dietary cholesterol, such as that found in eggs, goes straight to the bad stores in our blood. Prof Sanders points out that LDL cholesterol is typically marginally lower in vegans, who consume no cholesterol, so although dietary cholesterol does seem to have some effect on blood levels, it’s far from the only factor.
As Dr Harding explains: "Think of your cholesterol system like a big warehouse: you’ve got stuff you’ve shipped in and stuff you’ve made on site, but ultimately everything gets redistributed from the same place – and it’s that redistribution process that’s messed up in people with raised cholesterol."
As for what exactly triggers the processing problem, there are many possible explanations. For example, too much saturated fat changes the way the liver processes cholesterol, meaning LDL cholesterol isn’t taken out of the blood and broken down as easily. Raised cholesterol levels are also associated with getting older.
"But we don’t yet know if that’s because something naturally goes wrong with cholesterol metabolism as we age, or if it’s the cumulative result of 25 years of an unhealthy lifestyle," says Dr Harding.
LOOK AT YOUR FAMILY HISTORY
While there’s no need for most healthy adults to restrict their egg intake – the NHS, the cholesterol charity Heart UK and the British Heart Foundation all encourage eating them as they are "packed full of good stuff’ – some people do need to be a little more careful, says Sian Porter.
This includes those with the inherited condition familial hypercholesterolaemia, where they’re born with very high cholesterol levels due to gene faults. "Often, it’s diagnosed when someone in the family has a very early heart attack," Porter explains.
People with this are advised to limit cholesterol from food to 200mg a day – that would be one medium egg or less.
Even among healthy adults, how much cholesterol we absorb from food varies widely, says Dr Harding. There is a strong genetic component to this. For example, between a quarter and a third of the population inherit a version of the APOE gene called e4, that makes them much more sensitive to dietary cholesterol, with their levels of the bad sort more likely to rise after eating foods containing cholesterol.
But even people who carry this e4 gene variant can eat eggs without increasing their bad cholesterol, he says – as long as they consume plant sterols (found in vegetable oils, nuts and seeds) in the same meal.
"Plant sterols block cholesterol absorption and lower LDL cholesterol by up to 10 per cent," explains Dr Harding.
If you want to know if you have trouble metabolising cholesterol, "look at what your parents or grandparents died of", he advises. "If you’ve got a family with a history of heart disease, heart attacks and strokes, they probably had high cholesterol. And if so, be a bit more cautious about egg intake."
Porter adds that for those with high cholesterol, or who are at risk of cardiovascular disease: "It’s much more important to watch your saturated fat intake."
A NUTRITIONAL POWERHOUSE
Eggs "really are a nutritional powerhouse’, says Saunt, "and incredibly cheap’. Dr Harding, who eats between two and five eggs a week, agrees: "If you look at the fatty acids in egg yolk, around 50 per cent of this is oleic acid, which is the same healthy type as in olive oil.
"They’re also as good a quality source of protein as steak or chicken, for less money," he adds. A 100g egg has 12.5g protein, while 100g of chicken breast provides 32g and steak 31g.
Eggs are "incredibly nutrient-dense’, adds Sian Porter. This means they provide protein and a host of vitamins and minerals for relatively few calories, around 79g for a large egg – "providing they’re boiled or poached’.
While they’re high in cholesterol, they’re low in saturated fat – unlike, say, butter or cheese.
Sian Porter adds: "They’re one of the few foods that contain vitamin D (needed for healthy bones), as well as vitamin B12 and folate (both important for the nervous system and to make blood cells), vitamin A (for skin and eye health), riboflavin (which helps release energy from food) a little iron, plus iodine (important in pregnancy for the baby’s brain), which many teenagers and young women lack."
DON’T DITCH THE YOLK
While the fat and cholesterol comes from the yolk, the egg white is mostly protein and water and, therefore, much lower in calories. "That’s why there was such a fashion for egg-white omelettes at one point," says Porter.
"But throwing away the yolk is madness, as you’re missing out on the bulk of an egg’s nutrients, including vitamin D.
"Nature is very clever in the way it gives you food as complete packages," she adds. "Vitamin D is a fat-soluble vitamin, which means your body needs fat to absorb it; and in an egg, the vitamin D comes together with the fat in the yolk."
A small study at the University of Illinois, published in the American Journal of Clinical Nutrition in 2017, compared 10 men who were given the same amount of protein, either as whole eggs or just egg white, after a weight-lifting workout. Those who had the whole eggs showed a 40 per cent greater reaction in muscle-building response afterwards.
HOW YOU COOK THEM MATTERS
The important thing isn’t how many eggs you eat, it’s how you prepare them, says Porter.
"A great, healthy option when you don’t have much time is to break an egg into a mug, whisk it up, add a little dot of fat if you want, then microwave it for 45 seconds for an instant omelette."
Making a traditional omelette, scrambling eggs in a non-stick pan (rather than adding lots of butter or oil), baking or poaching are also great ways to cook eggs, she says. "Especially if you can add lots of vegetables, too."
So crack on!
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