Back to basics: Eggs

Hen eggs have long been a staple in diets around the world, prized for their versatility, affordability, and nutrient density. Eggs can be eaten in meals, or used as a cooking ingredient in a wide range of composite foods. They are also one of the more affordable animal protein sources. However, conflicting information about the health effects of egg consumption has led to debates and controversies, with public opinion sometimes lagging behind the ever-evolving research. Concerns about dietary cholesterol, cardiovascular disease risk, type 2 diabetes mellitus risk, and food allergy risk in children have been fuelled by conflicting studies. This has led to confusion about the benefits or harms of consuming eggs. This article aims to give an overview of the current thoughts and evidence regarding egg consumption and provide some practical advice.

Egg nutrition

Eggs are a moderate energy, nutrient-dense food providing on average 66 kcalories, high-quality protein (6.4 g), and a wide range of micronutrients per egg (1). A medium-sized egg contains 4.6 g of total fat and is considered a good source of unsaturated fatty acids. Eggs are also rich in dietary cholesterol, providing around 177 mg per egg. Eggs contain the micronutrients pantothenic acid, phosphorus, vitamin A, and folate. In addition, eggs are also high in vitamin B12, biotin, riboflavin, selenium, and iodine. choline, vitamin D, folate, and iodine. (2). Egg yolk is one of the few naturally occurring food sources of vitamin D and the lipid matrix is believed to enhance the bioavailability of yolk phytonutrients, such as lutein and zeaxanthin (2).

Egg protein

Eggs are considered a source of high-quality protein since they contribute all nine essential amino acids. Objective measures of protein quality and digestibility give a high value for eggs (97%), which is similar to that applied to other high-value animal protein sources such as milk and cheese (95%) and meat (94%) (3). The protein in eggs can meaningfully contribute to increasing one’s overall protein intake which could beneficially affect protein metabolism and conserve lean mass. Recent research indicates that proteins that are quickly broken down after consumption, with a high essential amino acid content and sufficient leucine are most effective in promoting muscle protein synthesis (4). Eggs fit these criteria, containing all essential amino acids, are quickly digested, and contain around 1341 mg of leucine. Additionally, an adequate protein intake is of particular importance for older adults in order to prevent muscle loss and risk of frailty (5). Eggs provide an easily accepted, low-cost, easily prepared, and consumed protein source option for this age group.

For more information about protein and health see: https://www.healthfullymyself.com/post/spotlight-on-protein-and-are-you-really-getting-enough

Controversies surrounding egg consumption

Body weight and obesity

Numerous studies have explored the relationship between egg consumption and body weight, with findings suggesting that eggs may play a role in weight management and obesity prevention. However, conflicting evidence exists regarding the impact of eggs on body weight in the context of overall dietary patterns and individual metabolic profiles. While some studies suggest that egg consumption is associated with lower body mass index (BMI) and decreased risk of obesity, others indicate no significant effect or even a potential increase in BMI with high egg intake. Therefore, further research is needed to clarify the mechanisms underlying the relationship between egg consumption and body weight regulation, taking into account factors such as dietary patterns, physical activity levels, and genetic predispositions

One study completed analysis by sex and found a decreased risk of being overweight or obese for females consuming what is considered a high egg intake (~50g/day) in contrast to those consuming no eggs (6). It should be noted that this effect was only found in the female participants, not the male ones. Conversely, two studies found no association between eggs and waist circumference (7,8).

To summarise the findings from these studies, it would appear that eggs at worst do not negatively affect body weight. At best, they can help manage and prevent against being overweight or obese.

Energy intake and satiety

The high protein content of eggs is thought to contribute to increased feelings of fullness and reduced food intake, which may support weight loss. Additionally, eggs are nutrient-dense and provide essential vitamins and minerals, making them a valuable component of a balanced diet for weight management. However, the evidence to support these claims still remains conflicted.

Three randomised controlled trials demonstrated that including eggs in breakfast led to reduced calorie intake throughout the day compared to a breakfast of equal calorie content with high carbohydrates (and no eggs) (9,10,11). Additionally, one found decreased appetite hormone signalling (9), and the other a decreased desire to eat in the subsequent 24 hours (10).  A 3-month study compared the effects of eating protein-matched breakfasts that were either high or low in eggs in participants with type 2 diabetes mellitus. The participants consuming the high-egg breakfast reported reduced hunger and increased satiety post-breakfast (12).

Conversely, two other studies found no differences in energy intake after an egg breakfast or lunch (13,14). While one found the participants had increased satiety after the egg lunch, this did not translate to a subsequent reduced energy intake (14).

Evidence from randomised controlled trials indicates that eggs are a satiating food that may reduce energy intake at subsequent meals. These effects could have a positive impact on weight management by helping to prevent body weight gain or supporting weight loss as part of an energy-restricted diet.

Cholesterol content

In the past, cholesterol was viewed as negatively impacting blood cholesterol levels, therefore increasing one’s risk of cardiovascular disease (CVD). With eggs being a significant source of dietary cholesterol, concerns over eggs and CVD risk were valid. However, recent research suggests that dietary cholesterol (from both eggs and other sources) has a minimal impact on most peoples’ lipid profile and that saturated and trans fats have a more significant influence on cardiovascular risk (15).

If this is in fact correct, then eggs’ high cholesterol content should not be a health issue, and with a low saturated fat content, eggs should be a healthy protein source. However, as we will see in the following section, the results surrounding egg consumption and CVD are still very divided.

The current guideline (supported by research) is that dietary cholesterol is not of concern. However, the fact that cholesterol, saturated fat, and animal protein often coexist in foods means that the interaction and independence between dietary cholesterol and these nutrients and their impact on various health measures still largely remains uncertain.

Cardiovascular health

The relationship between egg consumption and CVD risk is another grey area. The subject has been extensively studied and reviewed, and still, there is no clear answer. The majority of systematic reviews and meta-analyses observed no association between egg consumption and CVD risk (7,16,28,29,30,31). Similarly, the majority of studies that follow participants (often over long periods of time) have reported no association between egg intake and risk of cardiovascular disease (32,33,34). Some have even observed an inverse association with CVD (35,36). However, there still exist studies that identify an increased risk (37,38), particularly in people with diabetes (16,17,29).

The inconsistencies in study findings continue to fuel the controversy around the impact of egg consumption on CVD risk. To add to the confusion, those that do find an association are often at different consumption levels, sometimes ranging from 1 – 14+ eggs per week. Even after reading the studies, I struggle to offer any clarity or insight on the matter of eggs and CVD. Only from my observation, those studies that find an association between consumption and CVD, note it is usually in a dose-response manner (i.e... the more eggs that are consumed, the more the risk increases).

If you are particularly worried about your cardiovascular health, I would consider limiting egg consumption to a few times a week (or a maximum of one egg per day), and ensure that when you do eat eggs, they are part of a diet rich in whole-grains, fish, vegetables, and healthy fats. The differences in how eggs are consumed in the diet rather than eggs themselves is considered an important factor that is potentially responsible for so many conflicting results; this will be covered in later on.

Type 2 diabetes

Despite being extensively studied, the evidence regarding the association between egg consumption and the risk of type 2 diabetes (T2D) remains complex. There are several large meta-analyses from observational data that associate high egg consumption with an increased risk of T2D however, this cannot be stated conclusively due to multiple confounding factors (16,17).

For instance, one meta-analysis from multiple cohort studies found that infrequent egg consumption did not increase T2D risk, but suggests a slightly increased risk if consuming more than 3 or more eggs per week. However, this effect was restricted to USA populations only (18). Similarly, a more recent pooled cohort study (within USA populations only) found no increased risk with less than 2 eggs per week but an increased risk of T2D with egg consumption of 2 or more eggs per week (19). The current results are consistent with other meta-analyses in which a positive association between egg consumption and T2D risk was reported among US cohorts, but not among non-US studies (20,21,22). Another study based in China found that higher egg consumption was linked to an increased risk of T2D, particularly among those with a family history of diabetes (23).

Overall these findings are interesting; indicating that higher egg consumption may put only the US population and, less convincingly, Chinese populations, at increased risk of T2D. It is important to note that there is limited data supporting a biological mechanism underlying this association. Because of this, other confounding factors cannot be excluded. Possible explanations for why this increased risk is observed in USA and Chinese populations only are that many studies did not account for intakes of foods commonly consumed with eggs like red and processed meat, refined grains, and sugary beverages (particularly in the USA). Similarly, the authors of the study in China noted that the food habits of the Chinese population have been turning towards a diet of increased meat, oil, snacks, or energy-dense foods which was not accounted for in the studies.

In the context of all this, the association between high egg consumption with T2D risk remains possible but by no means conclusive.

Allergies

Egg allergies are relatively common, particularly in children, and can range from mild to severe reactions. Until recently, it was advised when weaning babies to delay introducing potentially allergenic foods; including eggs. However, there is growing evidence that early introduction of potentially allergenic foods may reduce the risk of allergy in babies and children (24,25). The current recommendation is that babies are exposed to potentially allergenic foods at the onset of weaning (26,27).

For babies deemed at higher risk of food allergy, the recommendation is to introduce and regularly expose them to cooked eggs from around 4 months of age (2).

A note about the variable findings

There is much speculation from scientists as to why studies examining eggs and health are so conflicted:

• With observational data (which has predominantly been used in these studies) it is difficult to assess the relationship of any individual food independently of a dietary pattern. Additionally, eggs are an especially difficult food as they are not only eaten in meals (e.g., omelettes), but they are also used as a cooking ingredient in a wide range of composite foods (e.g., cakes), and it is not always obvious if eggs are an ingredient or not. This makes tracking egg consumption for study purposes difficult.

• It is difficult to study food in isolation without considering the effect of other foods consumed in the diet. For example, in Western populations, eggs are typically consumed with meat, and sometimes other fried foods (think traditional American and English breakfasts) that are high in saturated fat. Conversely, in Asian cultures, eggs are frequently consumed in meals with vegetables. This may help to explain the observed link between eggs and T2DM in US populations but not others. It is also possible that Western populations consume more cholesterol from other sources (e.g., red meat, full-fat dairy, and discretionary foods), as compared to people from Asian cultures. Cooking methods are also different within the same and between different cultures. Higher temperatures and longer cooking times potentially lead to oxidative damage to the vitamins in eggs.

• Finally, few studies fail to consider the multiple factors at the farming level that can potentially influence the nutritional composition of eggs. For example, the chicken feed composition, or whether the chickens are free-range or caged.
  

All of these factors likely play some part in the wide range of study results.

What about just the egg whites?

All the conflicting information about the health effects of whole eggs might lead some to wonder if it's better to eat just the whites (which contain most of the protein) and avoid the yolks (which contain most of the fat and cholesterol). This is a valid question as the nutritional content of the yolk and the white differ substantially.

Egg whites are an excellent low-calorie source of high-quality complete protein, containing all essential amino acids. They only contain trace amounts of fat and no cholesterol. However, they are also low in vitamins and minerals in comparison to egg yolks. Conversely, egg yolks are higher in calories, are much lower in protein, are rich in fatty acids (saturated, monounsaturated, and polyunsaturated), and as we have discussed extensively, are high in cholesterol. However, egg yolks are nutrient-dense, contain most of the vitamins and minerals found in eggs, and are rich in antioxidants.

In the few studies I found comparing egg white, and whole eat consumption and health, one study found that the intake of whole eggs led to greater overall improvements in micronutrient diet quality, choline status, and HDL and overall blood profiles with minimal negative effects on insulin resistance compared to egg whites (39). The other review, examining body composition and strength, found that several studies found that whole eggs are indicated to have an advantage over egg whites in increasing muscle protein synthesis, improving markers of strength, and reducing body fat (40,41).

These studies indicated to me that while egg whites can be a useful way of adding protein to the diet, it is still important to incorporate them with whole eggs as well.

Final remarks

The ongoing debates and conflicting information about the health effects of eggs highlight the complexity of nutritional science. Despite their longstanding reputation as a nutrient-dense, affordable, and versatile food, concerns about cholesterol, cardiovascular disease, type 2 diabetes, and allergies have muddled public perception. Despite the controversies, current research supports the view that eggs have a positive or neutral impact on health markers and do not pose a risk when eaten regularly as part of a balanced diet. Whole eggs provide a broader range of nutrients compared to egg whites alone however, for individuals concerned about cardiovascular health or managing conditions like type 2 diabetes, it may be wise to monitor egg intake and focus on incorporating eggs into a healthful, balanced diet.

My best advice for most people, after taking all the current research into consideration, is that instead of fixating on removing a single food, such as eggs, individuals should focus on implementing a healthy dietary pattern rich in vegetables, fish, whole grains, and healthy fats.

Do you need help with your diet or nutrition, or are confused about how to make the best dietary changes to suit your individual health needs and lifestyle?

Feel free to contact me with any questions or to arrange a personal consultation:

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*Disclaimer*

The information presented in this article is for educational purposes only and based on my interpretation of the current research. Individuals with specific health concerns or dietary restrictions should consult with qualified healthcare professionals or registered dietitians for personalised guidance and recommendations tailored to their individual needs and circumstances.

References

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