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Eggs

Eggs have been the subject of debate in the nutrition world, having long been touted as the perfect food in some circles, and vilified by others for their cholesterol content, saturated fat, and potential for allergy or contamination. So which is it? We took a look at the literature to get to the yolk of the matter. Here’s what we found…

What’s in an Egg?

An egg is the unfertilized ovum produced through ovulation by a bird. In a fertilized egg, the yolk serves as the primary source of nutrients for the growing embryo, and the egg white, or albumin, is a protective layer that also provides additional nourishment. It’s no wonder that eggs contain a dense amount of nutritional value in a small package. That said, I’ll admit that I personally have found it a bit philosophically curious that humans eat the reproductive eggs of other animals, similar to the irony of drinking milk from other mammals.

Nutritionally, eggs have been a common, inexpensive source of high-quality proteins, unsaturated fat, folate, and various vitamins, as well as a major source of dietary cholesterol.

Nutritional Value

According to the USDA, 1 whole poached hen egg has the following macronutrient profile:

  • 6.25 g protein
  • 4.74 g fat, broken down into:
    • 1.8 g monounsaturated fat (MUFAs)
    • 1.6 g saturated fat
    • 0.95 g polyunsaturated fat (PUFAs)
    • with 185 mg cholesterol
  • 0.35 g carbohydrates
  • 0 g fiber

The Spectrum of Nutrients

The nutritional contents of eggs, which depend on quality, source, and cooking preparation, include an array of vitamins and minerals such as B vitamins, fat-soluble vitamins A, D, and tocopherols, the minerals zinc, selenium, potassium, calcium, and magnesium, in addition to carotenoids such as lutein and zeaxanthin. Eggs are also an important source of lecithin and contain high concentrations of choline.

Consuming whole cooked eggs with carotenoid-rich and vitamin E-rich foods, such as a raw mixed-vegetable salad, has also been found to be an effective way to increase the absorption of carotenoids, α-tocopherol, and γ-tocopherol.

Raw vs. Cooked

It is well established that cooking and processing will denature proteins, but how does the overall profile of eggs fare when cooked? According to USDA and WHFoods, the difference in nutrient values between one large raw egg and one large hard-boiled egg is significant, with raw eggs containing 33% more omega-3 fatty acids, 30% more lutein and zeaxanthin, and 23% more choline.

One study looked at the oxidative stability of omega-3 PUFAs in enriched eggs following cooking and storage. They found that the content of omega-3 fatty acids in boiled eggs was higher than in fried eggs, and lipid oxidation was significantly affected by the different cooking methods (with fried eggs containing higher levels of oxidation products such as malondialdehyde and cholesterol oxidation products).

In general, my personal take is that I am not a proponent of heating oil-rich food because of the damage that can occur to the fats. I also know that there are risks to eating raw eggs as you will read about below. It may be worthwhile to find some middle ground—not too much heat such as in frying eggs (where you can actually see the “browning” effects indicating oxidative damage), yet just enough to have them cooked.

Organic vs. Conventional: Is There a Difference?

Diet, sourcing, environment, and treatment of hens impact the nutritional contents of eggs. Conventional eggs are sourced from cage-raised hens and fed conventional feed, while foraging and outdoor exposure are mandatory components in organic egg production and pasture-raised hens.

Enriched eggs with higher “omega-3” content is derived most commonly through feed modifications for hens using various plants, such as canola, soybean, walnuts, and flaxseed, or marine products, such as fish oils, seaweed, or microalgae. The label “enriched” is not indicative of raising methods and hens can be either conventionally cage-raised or exposed to outdoor environments.

Several studies have compared the quality and composition of these various eggs and found significant differences in nutrient content:

  • In a study comparing the quality of organic eggs, eggs enriched in omega-3 fatty acids, and conventional eggs (cage-raised), researchers found the yolk of organic eggs contained the highest amounts of protein, potassium, and copper while the yolk of conventional eggs contained more magnesium and iron. Enriched eggs had yolks containing more calcium and manganese, and overall they contained a higher amount of omega-3 and MUFAs with a smaller saturated fatty acids content.
  • In a study that looked at vitamin A, E, and fatty acid composition of pasture-raised vs. caged hens, eggs of the hens that foraged grasses had twice as much vitamin E and long-chain omega-3 fats, 2.5 times more total omega-3 fatty acids, and less than half the ratio of omega-6:omega-3 fatty acids compared with caged hen eggs (suggesting that they are not as high in inflammatory fats). Vitamin A concentration was also 38% higher in the pastured hens’ eggs than in the caged hens’ eggs.
  • One study looking at how forage material (corn vs. herbs vs. kale) affected yolk color, fatty acid, and carotenoid composition of the egg yolk found that kale-fed hens led to higher amounts of omega-3s in yolk, 30-times higher lutein than in corn-fed hens, and 70-fold amount of β-carotene than corn-fed hens. Overall, the total content of carotenoids was twice as high in the egg yolks from hens fed on kale than in the other treatments.

Health Concerns

The Danger of Raw Eggs: Myth or Fair Warning?

While the nutrient content is generally higher in raw eggs compared to cooked eggs, there have been concerns regarding the potential hazards of consuming raw eggs.

Food-borne illness is a major concern, with eggs and egg-derived foods responsible for a large number of cases each year, mainly caused by Salmonella. Pasteurization is mandatory for any egg-derived foods or product.

However studies have demonstrated that Salmonella contamination is associated with various management and environmental factors, including induced molting, larger flock size (>30,000 hens), multi-age management, cage housing systems, high level of manure contamination, and egg production rate of >96%. Food-borne outbreaks of human salmonellosis have been traced back to consumption of Salmonella-contaminated shell eggs, with small farms having demonstrated a significantly reduced risk of contamination.

Some concern may be over anti-nutritional factors of raw eggs. Egg whites contain proteins such as ovomucoid which inhibit trypsin, and avidin which can bind biotin. These compounds are primarily found in the egg white, are heat-sensitive, and usually destroyed when cooked.

Cholesterol Conundrum: Eggs and Cardiovascular Risk

Eggs have been a controversial food due to the saturated fat content (about 3 g/100 g) and cholesterol content (about 200 – 300 mg/100 g). Inconsistent results of population-based (epidemiological) studies about the relationship of egg consumption and cardiometabolic diseases have historically made it difficult to establish a definitive conclusion.

However, subsequent research suggests that dietary cholesterol in general, including cholesterol in eggs, has limited effects on the blood cholesterol level and on CVD.

Clinical studies indicate that blood markers such as LDL-cholesterol and LDL/HDL ratio have the potential to be influenced by dietary cholesterol in the presence of factors like ethnicity, genetic makeup, hormonal factors, and body mass index. In summary, there may be individuals who would “hyper-respond” to dietary cholesterol, and those who would not. That said, we now know that the absolute lipid numbers are not as concerning as the particle number and particle size of these lipid compounds. In one study, having an egg every day for 30 days compared to not eating an egg did not negatively change atherogenicity of LDL-cholesterol. Rather, it seemed to be improved.

Dose-response: Too Much of a Good Thing?

The amount of eggs one consumes may play a role in plasma changes and disease risk:

  • In a meta-analysis looking at egg consumption and risk of cardiovascular diseases and diabetes, researchers concluded that there is a positive dose–response association between egg consumption and the risk of CVD and diabetes.
  • One study demonstrated two eggs per day did not adversely affect the biomarkers associated with CVD risk maintaining the LDL/HDL ratio when compared with an oatmeal breakfast, but it did increase satiety with a decrease in plasma ghrelin throughout the day in a young healthy population.
  • Researchers found that consuming ≥ 5 eggs/week was significantly associated with an increased risk of breast cancer compared with no egg consumption in a dose-response meta-analysis of prospective observational studies.

Additional Concerns

Allergenicity

Hypersensitivity to chicken egg is the second most common food allergy in children, next to cow’s milk and primarily caused by hypersensitivity to four allergens found in the egg white: ovomucoid, ovalbumin, ovotransferrin, and lysozyme. However, some research suggests certain allergens found in the egg yolk may play a role as well.

  • Strong risk factors for infantile egg allergy include history of allergic disease in an immediate family member and having parents born in East Asia.
  • Exposure in the first year of life to siblings and dogs may decrease the risk of egg allergy.
  • Various studies have found heated egg whites may be better tolerated by those allergic to eggs, and, further, approximately 70% of children with the allergy will outgrow it by 16 years of age.
  • One study found that Epstein-Barr virus (EBV) might be implicated in food allergy—researchers concluded that high expression of EBV-specific antibody and miRNAs in patients with egg allergies suggested that EBV infection could potentially play a promoting role in IgE-mediated egg food allergy.

As a side note, I wonder whether the preponderance of gluten-free (typically higher egg density) products that are now on the market are going to increase exposure to egg, ultimately potentially resulting in a greater risk of egg intolerance and/or allergy.

Toxicity

Unfortunately, it’s difficult to escape the reality that environmental toxins exist in the food supply, and egg production is by no means exempt. In conventional eggs, there is the potential presence of pharmaceutical drugs, and exposure to contaminants such as persistent organic pollutants or dioxins can even be found in free-range and organic eggs, depending on various factors and habits within production, including soil quality.

Despite this fact, some researchers conclude that the nutritional benefits of egg consumption outweigh risk from exposure to toxins and that the health risk from regular consumption must be assessed within the context of the individual’s overall diet and level of exposure.

Key Takeaways

Always check with your health professional to explore foods that are best for you if you are unsure. I don’t believe in ruling out eggs for everyone. Personalized eating and food choices is the best approach based on what we know about nutrigenomics, environmental factors, and allergic response. For some, eggs can be a healthy functional food when choosing well-sourced products and when all personal risk factors are taken into consideration.

Here are some final takeaways:

  • Choose organic and pasture-raised eggs from smaller farms whenever possible for a better nutrient profile and less risk of contamination.
  • When cooking eggs, avoid oxidation of fatty acids and decreased nutrient profile with lower temperature cooking and reduced cooking time, such as poached or soft-boiled (avoid frying eggs).
  • Take a “Goldilocks approach” to consumption amount—not too little, not too much.
  • Try to rotate foods every 3 – 4 days, preventing excessive consumption of eggs, especially if you are on a gluten-free or Paleo-style diet.
  • If you suspect allergy or sensitivity to eggs, work with a healthcare professional to get testing done.

If you’re curious about my personal take—I avoid them due to an egg allergy that developed later in life.

 

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