Eating eggs

By Dr. Shireen Kassam and Dr. Zahra Kassam

Eggs are a healthy source of protein, aren’t they?

It is common to hear that eggs are a healthy protein source. This stems from the fact that egg whites provide a source of ‘complete’ protein and that this comes packaged with a relatively low saturated fat content when compared to other sources of animal protein. One large egg (50 grams) contains 6 grams of protein and around 1.5 grams of saturated fat when compared to a 70-gram serving of beef which has around 4 grams of saturated fat. Protein can be more satiating than carbohydrate and fat, in part due to differential effects on gut hormones that provide us with signals of fullness, although the science on this topic is mixed and results certainly are not consistent.^1,2 Nonetheless, when it comes to egg consumption, typically for breakfast, interventional studies suggest that eggs are associated with improved satiety compared with breakfasts such as cereal or bagels, which then results in a reduced calorie intake during the remainder of the day.^3-5 Interestingly, this effect does not seem to be specific to egg protein or indeed animal sources of protein. When the satiating impact of different protein sources were compared in 12 healthy subjects, it was found that egg, albumin, casein, gelatin, soya and pea protein had an equivalent effect.⁶ Both Quorn (mycoprotein) and soya have been compared to chicken and shown to be superior in their satiating effects.⁷ This suggests that it is not necessarily the egg or animal protein per se that produces satiety, but protein in general. Given the huge benefits to health associated with swapping animal protein for plant sources of protein, it seems tofu scramble is the better breakfast choice.⁸

Eggs are a source of healthy nutrients, aren’t they?

Most of the nutrients in eggs are contained in the yolk. These include B vitamins, including vitamin B12, vitamin D, iodine (if added to chicken feed), selenium, biotin, choline, lutein and zeaxanthin (carotenoids).⁹ However, these individual nutrients themselves do not make a food healthy. The whole package and its impact on the body is more important. Eggs comes packaged with a sizable portion of cholesterol, around 200mg, and more saturated fat than plant foods, ‘nutrients’ we don’t really want to be consuming. The more important question to ask is how eggs compare to other foods that contain similar nutrients but different packaging. What would happen to health outcomes if eggs were substituted for another food? Observational studies that have conducted substitution analyses have clearly answered this question. One such large study including more than 400,000 men and women followed for 16 years found that just substituting 3% of energy from eggs for plant sources of protein could reduce the risk of dying by 18% to 45% in men and 20% to 39% in women.¹⁰ Another substitution analysis combining the results of six studies and included 29, 682 participants followed for around 19 years showed that substituting eggs just once a week for virtually any other foods other than processed meat led to reductions in cardiovascular disease and risk of dying from all causes. When substituting 1 egg per day with whole grains, legumes, nuts or fish, there were even bigger gains with swapping out eggs for nuts lowering the risk of cardiovascular disease by 21% and risk of dying from all causes by 22%.⁸ These types of substitution studies demonstrate that plant sources of protein are better for health than egg whites, often considered to be a healthy source of protein without the harms associated with the consumption of the egg yolk.

One major concern with regards the body’s handling of the nutrients in eggs is related to choline. In people consuming an omnivorous diet, gut bacteria convert choline to trimethylamine (TMA). This is absorbed into the blood and converted into trimethylamine oxide (TMAO), a substance that has been intimately associated with the development of atherosclerosis, heart failure, type 2 diabetes and kidney failure.^11–15 In contrast, those consuming a 100% plant-based diet do not have the required bacteria to form these substances and choline from plant foods does not get converted into TMAO.¹⁶ Whether TMAO is actually causing these chronic conditions or merely an associated factor reflecting a poor quality diet remains an open question, but it’s clear that eating a diet that keeps TMAO levels low is better for long-term health.¹³

The other aspect to consider is food safety, such as the risk of transmission of unwanted substances, whether they are environmental toxins, pollutants or infections. When it comes to eggs, they don’t fare well in this regard. In 2018, there were nearly 50,000 cases of foodborne infection in the European Union with 1 in 3 cases caused by Salmonella, mainly linked to the consumption of eggs.¹⁷ In Canada 1 in 8 people (4 million Canadians) get sick each year from contaminated food, with over 11,500 hospitalizations and 240 deaths each year due to food-related illnesses mainly from animal products, of which 1 in 4 are due to Salmonella.¹⁸

Although eggs may be better for health compared to a bacon sandwich with white bread, we can make healthier and safer choices by eating plant sources of the same nutrients. For example, an 80g serving of tofu has 6g of protein and contains choline, selenium and iron whilst being very low in saturated fat and containing no cholesterol.

What impact do eggs have on blood cholesterol levels?

Another ongoing debate is the impact of dietary cholesterol on health. Given that eggs are high in cholesterol, with a large egg containing around 200mg, they are often used to either defend or refute the claim. Vegans argue that because eggs are high in cholesterol, they must be a cause of heart disease. It seems that in recent years, dietary guidelines have de-emphasised the harm of dietary cholesterol with a greater focus on the overall dietary pattern.¹⁹ This does not mean that dietary cholesterol no longer matters, it just means that other components in the diet have a greater impact on health outcomes. Namely saturated fat. The impact of saturated fat consumption in the diet has a far greater and more predictable effect on blood cholesterol levels and hence the risk of cardiovascular disease than dietary cholesterol.²⁰ The relationship between saturated fat and blood cholesterol levels is pretty much linear.²¹ The more you eat the higher the blood cholesterol level. This is not the case for dietary cholesterol. If you are already eating a diet relatively high in cholesterol, like the typical Western diet, then adding a bit more won’t affect blood cholesterol levels. However, if you are eating a diet free of cholesterol – that is a vegan diet – then adding an egg or two into the diet will raise blood cholesterol levels. The impact of dietary cholesterol from a food like eggs is greater when the diet is already low in cholesterol. At higher intakes of cholesterol, the impact on blood cholesterol plateaus and thus eating more doesn’t make a great deal of difference.

Having said all this, it does not mean that dietary cholesterol is healthy or necessary. Our body makes all the cholesterol it needs. You do not need to eat any. Blood cholesterol levels are lowest in those following a vegan or predominantly plant-based diet, especially when the diet is centred around whole plant foods.²² Omnivores with high blood cholesterol levels can lower levels as effectively as medication by adopting a healthy plant-based diet alone, which is one of the reasons why those eating a plant-based diet have some of lowest rates of heart disease of any diet pattern.²³

So back to the question of eggs. It really depends on the quality of the rest of the diet. Overall, the science shows that up to one egg a day is probably okay but above that level there are detrimental effects on blood lipids. This is on the basis of an updated meta-analysis of 66 randomised studies, so good quality data, demonstrating that egg consumption does indeed elevate blood total and LDL-cholesterol levels.²⁴

What impact do eggs have on the risk of cardiovascular disease and type 2 diabetes?

A key question is whether egg consumption contributes to an increased risk of chronic illness. The answer is yes. A large analysis combining results of six studies in which of 29,615 adults were followed for a median of 17.5 years showed that each additional half egg consumed per day was associated with a 6% higher risk of cardiovascular disease and an 8% increased risk of dying from all causes.²⁵ A further study including 521,120 participants showed that each additional half egg consumed per day increased the risk of dying from cardiovascular disease, cancer and indeed all causes by 7% and that these negative impacts on health were predominantly due to the cholesterol content of the egg.²⁶

There is more certain evidence to show that egg consumption increases the risk of developing type 2 diabetes in Caucasian and non-Caucasian populations. In people with type 2 diabetes, eggs cause further harm by significantly increasing the risk of cardiovascular disease. There have been three meta-analyses assessing the impact of egg consumption on the risk of type 2 diabetes which together confirm an 18-42% increased risk in those eating 1 or more eggs per day.^27–29 In addition, in people living with type 2 diabetes, those consuming the most eggs were shown to have a 40% increased risk of cardiovascular disease.²⁸

We also need to remember that the interpretation of many studies on eggs is clouded by the fact that they are funded by the egg industry. Despite the studies showing unfavourable impacts on blood lipid levels, those funded by the egg industry appear to considerably downplay these effects, often by using statistical manipulations to produce more favourable results.³⁰

The bottom line. Consumption of eggs is not necessary. The literature can appear confusing and is complicated by industry funding. There is certainly enough data to cause concern regarding the negative health impacts of consuming eggs. We would suggest to you that eggs are best left off the plate.

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REFERENCES

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