Tuesday, July 7, 2015

Egg-Ology Today: The Underappreciated Health Benefits of Egg Phospholipids, Proteins & Antioxidants in the Yolk

The yolk is where almost all the "good" stuff in the eggs resides. Throwing the yolk of the 1-2 eggs you eat per day away, as people have been doing it for decades is thus madness.
For decades eggs have been falsely accused of being the drivers of the heart disease epidemic (cardiovascular disease claims upwards of 17 million lives worldwide each year | WHO. 2011). More recently, however, the small "cholesterol bombs" have been acquitted of all charges and scientists begin to (re-)evaluate their already know, but largely ignored health benefits. Health benefits that are not solely related to their high protein content, by the way.

As a SuppVersity reader you will know that eggs are valuable protein sources, but don't worry: This is not what today's SuppVersity article is about. Rather than that I would like to highlight a much less-known egg constituent, the egg phospholipids.
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Studies indicate that eggs are the major source of phospholipids (PL) in the Western diet; the same phospholipids that "have emerged as a potential source of bioactive lipids that may have widespread effects on pathways related to inflammation, cholesterol metabolism, and HDL function" (Blesso. 2015).
Table 1: Typical Composition of Egg Phospholipids | FA, fatty acid; LysoPC, lysophosphatidylcholine; LysoPE, lysophospha-tidylethanolamine; PC, phosphatidylcholine; PE, phospha-tidylethanolamine; PI, phosphatidylinositol; PL, phospholipid; SM, sphingomyelin. (Blesso. 2015)
"PL are key components of all biological membranes and are abundantly found in the diet, primarily as glycerophospholipid and sphingolipid classes. Dietary glycerophospholipids are made up of two fatty acids (FA), a glycerol backbone, a phosphate group, and a polar organic molecule (choline, serine, inositol, or ethanolamine).[...] The average large egg contains approximately 1.3 g of PL, which are almost exclusively found in the yolk. 
An egg breakfast improves the levels of triglycerides in active indiv. compared to an isocaloric bagel breakfast (Clayton. 2015).
Egg vs. oatmeal (more) and egg vs. bagel: You will probably still remember my recent article about a study by Ballesteros, et al. (2015) showing that an egg per day improves inflammation when compared to an oatmeal-based breakfast without increasing other cardiometabolic risk factors not just in healthy, but even in diabetic patients (read more | Ballesteros. 2015). In a similar, but more complex study, Clayton et al. (2015) found that compared to an isoenergetic breakfast with bagels, a daily breakfasts that includes two eggs will improve plasma triglycerides in active (resistance training) men and women.
A typical Western diet contains about 2–8 g of dietary PL per day. Estimates of average egg intake in the U.S. indicate that egg-derived PL contributes 10%–40% (or 0.8 g) of daily consumed PL. The major PL species found in egg include PC, phosphatidylethanolamine (PE), SM, and phosphatidylinositol (PI). The typical PL composition of egg is shown in Table 1, which reveals PC as the predominant species making up almost three quarters of the total PL. The typical FA compositions of egg PL species vary and are shown in Table 1" (Blesso. 2015).
Alongside carotenoids lutein and zeaxanthin, two potent anti-oxidant agents in eggs, and the previously mentioned phospholipids which have also been shown to
  • Eggs have beneficial effects on cholesterol in your cells | learn more
    decrease serum cholesterol levels in rats (Murata. 1982) and a reduction of the intestinal absorption of cholesterol (Jiang. 2001), 
  • improve memory retention and increase acetylcholine concentrations, a neurotransmitter that decreases in concentration in cases of Alzheimer’s disease (Masuda. 1998;  Favreliere. 2003), as well as 
  • improve liver function, and cancer prevention (Gutierrez. 1997),
there are also a hand full of peptide / proteins and related agents - mostly in the yolk of eggs - that make eggs a totally underestimated health food:
  • Table 2: Biological acitivities of egg proteins (Kovacs-Nolan. 2005)
    yolk proteins - ovalbumin, ovotranserin, ovucoid, ovomucin, lysozyme, as well as ovoinhibitor, vomacroglobulin, ovomacroglobulin and avidin have antibacterial activity and antihypertensive, immunomodulating, antiadhesive (=interferes with a key step of inflammation), antitumor, and antiviral activities (to find out what does what, check out Table 2 from Kovacs-Nolan. 2005);
  • immunoglobulins - specifically immunoglobolin Y from egg yolk which has been shown to have antibacterial activity, antiviral activity, can reduce the incidence of dental caries, is used in anti-venoms, acts as an anti-inflammatory agent, and serves as a carrier for anti-cancer drugs (Mine. 2004);
  • other components of the yolk - including phosvitin, sialyloligosaccharides and sialylglycopeptides, as well as the yolk lipids, lipoproteins, fatty acids, and cholesterol have scientifically proven antioxidant and antibacterial activities, as well (Kovacs-Nolan. 2005)
Men and women with familial hypercholesterolemia have a lack of / defective LDL receptors and a defective regulation of  the endogenous cholesterol production. For them reducing the intake of cholesterol and taking statins is in fact a good idea (Goldstein. 2015). The same may go for people with various other specific genetic polymorphisms a dozen of which have recently been summarized by Abdullah et al. (2015).
For 99% of us, there's no reason to be afraid of the cholesterol in eggs: Unfortunately, there's a small portion of the population whose genes predispose them to "abnormal" increases in serum cholesterol in response to increased cholesterol intake. Next to familial hypercholesterolemia (Goldstein. 2015), there are a number of other - albeit less threatening - polymorphisms (e.g. the ABCG5 polymorphism | Herron. 2006; see Abdullah. 2015 for a summary) which may explain why most (e.g. Nakamura. 2006), but not all studies refute the claim that an increased egg consumption triggers increases in cholesterol and subsequent increases in CVD risk in healthy indiv.

If you take a look at more general studies, and the negligible 0.38% increase of the LDL:HDL ratio McNamara et al. (2000) calculated per 100mg increase in cholesterol intake in their meta-analysis it is no wonder that all, not just "egg centered" epidemiological studies show that "dietary cholesterol is not related to coronary heart disease incidence or mortality across or within populations" (McNamara. 2000).

This does not mean that I recommend consuming 20 whole eggs per day. Especially for those of you who consume high amounts of carbohydrates, this may turn your diet into a highly unfavorable high fat + high carbohydrate diet, but 1-2 whole eggs a day ain't no problem; irrespective of what the rest of your diet looks like (assuming you don't belong to the previously mentioned group of people who are genetically disposed to have problems with their lipid metabolism) | Comment
References:
  • Abdullah, Mohammad MH, Peter JH Jones, and Peter K. Eck. "Nutrigenetics of cholesterol metabolism: observational and dietary intervention studies in the postgenomic era." Nutrition reviews (2015): nuv016.
  • Ballesteros, Martha Nydia, et al. "One Egg per Day Improves Inflammation when Compared to an Oatmeal-Based Breakfast without Increasing Other Cardiometabolic Risk Factors in Diabetic Patients." Nutrients 7.5 (2015): 3449-3463.
  • Blesso, Christopher N. "Egg Phospholipids and Cardiovascular Health." Nutrients 7.4 (2015): 2731-2747.
  • Clayton, Zachary S., et al. "Influence of Resistance Training Combined with Daily Consumption of an Egg-based or Bagel-based Breakfast on Risk Factors for Chronic Diseases in Healthy Untrained Individuals." Journal of the American College of Nutrition 34.2 (2015): 113-119.
  • Favreliere, S., et al. "DHA-enriched phospholipid diets modulate age-related alterations in rat hippocampus." Neurobiology of aging 24.2 (2003): 233-243.
  • Goldstein, Joseph L., and Michael S. Brown. "A Century of Cholesterol and Coronaries: From Plaques to Genes to Statins." Cell 161.1 (2015): 161-172.
  • Gutierrez, M. A., H. Takahashi, and L. R. Juneja. "Nutritive evaluation of hen eggs." Hen eggs, their basic and applied science. 2nd ed. CRC Press, New York (1997): 25-35.
  • Herron, Kristin L., et al. "The ABCG5 polymorphism contributes to individual responses to dietary cholesterol and carotenoids in eggs." The Journal of nutrition 136.5 (2006): 1161-1165.
  • Jiang, Yongzhi, Sang K. Noh, and Sung I. Koo. "Egg phosphatidylcholine decreases the lymphatic absorption of cholesterol in rats." The Journal of nutrition 131.9 (2001): 2358-2363.
  • Kovacs-Nolan, Jennifer, Marshall Phillips, and Yoshinori Mine. "Advances in the value of eggs and egg components for human health." Journal of agricultural and food chemistry 53.22 (2005): 8421-8431.
  • Masuda, Y., et al. "Egg phosphatidylcholine combined with vitamin B 12 improved memory impairment following lesioning of nucleus basalis in rats." Life sciences 62.9 (1998): 813-822.
  • McNamara, Donald J. "The impact of egg limitations on coronary heart disease risk: do the numbers add up?." Journal of the American College of Nutrition 19.sup5 (2000): 540S-548S.
  • Mine, Yoshinori, and Jennifer Kovacs-Nolan. "Biologically active hen egg components in human health and disease." The Journal of Poultry Science 41.1 (2004): 1-29.
  • Murata, Masakazu, Katsumi Imaizumi, and Michihiro Sugano. "Effect of dietary phospholipids and their constituent bases on serum lipids and apolipoproteins in rats." The Journal of nutrition 112.9 (1982): 1805-1808.
  • Nakamura, Yasuyuki, et al. "Egg consumption, serum total cholesterol concentrations and coronary heart disease incidence: Japan Public Health Center-based prospective study." British Journal of Nutrition 96.05 (2006): 921-928.
  • World Health Organization. Global Status Report on Noncommunicable Diseases 2010; World Health Organization: Geneva, Switzerland, 2011.