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Metafact Review: Eggs
Humans have eaten eggs for millions of years, initially from wild birds including pigeons and fowl, and later from domesticated birds like chickens. We have been raising chickens since 7000 BC, and their eggs are a major component of diets around the world.
Eggs are one of the most versatile cooking ingredients we have - they can be scrambled, poached or fried on their own, or combined with other ingredients to make cakes, pies and mayonnaise (just to name a few).
Many of us eat eggs daily, but what effect is that having on our health? Can eggs help with weight loss? Are they good or bad for heart health? Do eggs need to be stored in the fridge? We asked scientists to share the facts on eggs, here is what we found.
This review was co-written by Associate Professor Cornelie Nienaber-Rousseau, an expert in nutrition and cardiovascular disease from North-West University
$248,000,000,000: Global market for eggs in 2022
26: Hours for an egg to fully form
250: Number of eggs hens can lay in a year
74: Calories in one hard-boiled egg
6%: Proportion of recommended daily dose of Vitamin A
What’s in an egg?
One medium chicken egg contains about 70 kilocalories of energy. It also contains a significant amount of protein, approximately 6 grams per egg. Whether scrambled, fried, boiled or poached, eggs are a superb source of vitamins and nutrients.
Egg yolks are high in fats, because their biological purpose is to provide developing chick embryos with nutrients and energy. One of the fats they contain is cholesterol, which means that for many years eggs were considered unhealthy and could increase your risk of cardiovascular disease, a relationship which has since been contented.
Egg whites are made of 92% water, with a mixture of around 148 different proteins, and almost no fat or carbohydrates. 94% of proteins obtained from eggs become incorporated into the proteins of the body. Eggs are an important source of minerals such as phosphorus and zinc, and vitamins such as vitamin A, B12, D and pantothenic acid.
Not all eggs are the same - the nutrient content of eggs vary according to the diet of the hen.
Eggs are relatively low-cost, and are considered the most affordable protein source. For this reason their consumption is encouraged, especially when money is limited, to ensure adequate consumption of proteins and nutrients.
Do eggs help suppress hunger?
When battling with hunger pangs associated with weight loss diets, high-protein foods are known to reduce appetite and increase fullness (satiety). Several studies have indicated that eggs, because they are protein-rich, can suppress hunger.
Professor Maria-Luz Fernandez, an expert in nutrition from Connecticut University, says “I conducted a study in which we used two types of breakfast, one was egg-based and the other bagel-based, the number of Kcal [calories] were the same… Subjects had lower levels of ghrelin (appetite hormone) after the egg breakfasts, and they ate 400 less kcal in the next 24 hours after the egg breakfast.”
Several similar studies have found that breakfasts containing eggs suppressed hunger more effectively than wheat based breakfasts, oatmeal or cereal. "Based on the evidence form the experimental studies" says nutrition scientist Dr Cornelie Nienaber-Rousseau, "the incorporation of eggs into breakfast may be more effective than cereal or grain-based breakfasts to increase feeling full for longer and to limit short term energy consumption. However, the potential role of a routine egg breakfast in producing a sustained energy deficit and consequent weight loss, should be determined by additional research."
Can eating eggs help you lose weight?
Eggs help suppress appetite, so can they make you lose weight? Unfortunately, the relationship between eating eggs and weight loss is not yet clear.
Vander Wal and co-workers (2008) studied the effect of an egg-based breakfast as compared to a bagel breakfast on weight loss in overweight men and women following a weight loss diet. They found that after 5 weeks those consuming an egg breakfast had a 61% greater reduction in body mass index (BMI), a 34% greater reduction in waist circumference, and a 65% greater reduction in weight loss than those ingesting a bagel breakfast.
However, other studies have not come to such clear conclusions. Professor Peter Clifton, an expert in nutrition and endocrinology from South Australia University, says “There is good evidence of increased satiety from protein in general and eggs in particular. However, in a calorie-controlled diet the additive effect of protein is not seen and weight loss is the same after 3 months”
Incorporating eggs into breakfast may be more effective than cereal or grain-based breakfasts to increase feeling full for longer and to limit short term energy consumption. However, whether routine egg breakfasts can help weight loss needs to be determined by additional research.
Are eggs bad for heart health?
There has been a lot of debate as to whether eggs are bad for heart health. A few years ago recommendations were not to eat more than a few eggs a week on the grounds that eggs contain lots of cholesterol - about 185 mg per egg yolk, which is more than half the daily recommended amount. At the time, it was believed that elevated circulating blood cholesterol is caused by cholesterol in our food. Since then scientists found that most of the excess cholesterol in our blood is produced by the liver in response to eating too much saturated fat (fats that are hard at room temperature) such as the fat in bacon. So perhaps we need to eat less of the bacon, not the eggs, for breakfast.
However, Dr John David Spence, an expert in heart disease from Robarts Research Institute in Canada, disagrees. He says even if blood cholesterol is not raised after eating eggs, they are unhealthy because "for four hours after a high fat/high cholesterol meal, there is a marked increase in oxidation of LDL into the bad form, the arteries are twitchy, and the arteries are inflamed." Dr Spence also describes how egg consumption is associated with increased trimethylamine-N-oxide (TMAO) production, which may be an important predictor of heart disease.
Several studies have measured the incidence of heart disease in people who consume different amounts of eggs. One meta-analysis found that there is an elevated risk of heart failure with frequent egg consumption. A different meta-analysis found that intake of up to 1 egg a day may be associated with reduced risk of total stroke, but no clear association was found between egg intake and risk of heart disease.
Some of these different conclusions can be explained by the difficulties in measuring the relationship between eating eggs and heart disease. Self-reported egg consumption using food frequency questionnaires might introduce errors when people struggle to remember exactly what they ate when. Accounting for cooking methods and additives when eggs are prepared is also difficult. One way of addressing these issues is to conduct experimental feeding trials where diets are strictly controlled and then the incidence of disease is measured. Experimental studies like these are able to show cause and effect, but they are extremely expensive and challenging to do.
Like any food, eggs are bad for health if eaten in excess or as part of an unhealthy diet. Excluding eggs may be a good choice for people already at risk of heart disease as a way of reducing fat and cholesterol intake, but for many other people cutting out eggs may mean missing out on essential nutrients.
Are eggs gluten-free? Yes
Are eggs chicken periods? No, chickens are not mammals so don't have periods or wombs.
Do you need to keep eggs in the fridge? Eggs should be kept below 20'C, so for most kitchens out of the fridge is fine. However many say best practice is to keep them in the fridge so they last longer.
Do eggshells stop slugs from eating garden plants? Many people sprinkle eggshells around their flowers to stop slugs reaching the plants and eating them. Unfortunately, this hack is a myth.
Eggs do not need to be kept in the fridge, but it might make them last longer
Eggs likely help suppress hunger
We don't know if eating eggs can help with weight loss
Eggs are not bad for heart health when eaten as part of a healthy diet
Eggs are a cheap and rich source of nutrients and protein