Egg Consumption and Behavior

What came first, the chicken or the egg, or the bioactive components within the egg which are potent enough to affect behavior?

An egg may seem simple, one part white and one part yellow, but, if you zoom in a little closer, you will notice that an egg is filled with powerful bioactive compounds which are potent enough to affect health, learning, memory, and even mood!

In this article, we will review interesting scientific findings involving the egg, how certain egg components affect behavior and the tests used to reach such conclusions, as well as review limitations and future directions within this domain of research.

What came first, the chicken or the egg, or the bioactive components within the egg which are potent enough to affect behavior?

Eggs’ Diverse Nutritional Profile

Eggs are functional foods made up of components such as carotenoids (lutein and zeaxanthin), egg phospholipids, cholesterol, and bioactive proteins.^[1] So, there are plenty organic compounds lodged within those eggshells which warrant further scientific investigation!

Egg Peptides Decrease Hypertensive Rats’ Anxious Behaviors
Angiotensin converting enzyme (ACE) is an enzyme with an important role in the renin-angiotensin system (RAS), a system that regulates blood pressure. Scientists have demonstrated that certain foods (such as eggs,^[2] sweet potatoes,^[3] and milk^[4]) contain bioactive compounds which can inhibit ACE. A drop in ACE concentration is associated with reduced blood pressure, thus bringing about an anxiolytic or relaxing effect.^[5]

In particular, three egg peptides have been noted to possess anxiolytic properties by inhibiting ACE and they are:

Thr-Asn-Gly-Ile-Ile-Arg (TNGIIR)
Arg-Val-Pro-Ser-Leu (RVPSL)
Gln-Ile-Gly-Leu-Phe (QIGLF).

Few-Important-Egg-Chemical-Compounds-phosphatidylcholine anxiety

To further investigate the exact effects of these egg peptides, researchers used rats to test several dosage levels (ranging from 5 to 50 mg kg−1) of the egg peptides on anxious-like behavior in hypertensive rats as assessed by the behaviors elicited during an Elevated Plus Maze test.^[5]

Using the elevated plus maze test, the researchers determined which peptide dosage had anti-anxiety behavioral effects. Some measurements collected during the experiments included how much time the rats spent in the closed and open arms of the maze, the total distance traveled, and the total time spent in the maze’s center zone. Since animals naturally prefer enclosed spaces, spending more time in the open portion of the maze is considered to be a sign of decreased anxiety.

Only two of the three peptides, TNGIIR and RVPSL, were shown to affect ACE concentration levels and lowered anxiety-like behavior when administered at dosages of 50 mg kg−1. The TNGIIR-treated experimental rats spent a longer time in the open arms of the maze when compared to the control group. The RVPSL-treated experimental group (at dosages of 50 mg kg−1) exhibited similar behavior with the control group with respect to how many open-arm entries they performed.

The applications of this are interesting. Certain egg white peptides have anti-stress and anti-stress properties, taking the egg as a functional food to the next level.

Egg Phosphatidylcholine Improves Memory of Mice with Dementia

One question warranting research is how do certain egg bioactive compounds affect other chemical compounds found in the human body (which in turn may have the ability to impact both health and behavior).

In one experiment, researchers focused on egg-derived phosphatidylcholine, a compound (as its name implies) related to choline, and how it affects mice with dementia.^[6]

Mice underwent two behavioral protocols, Open Field test and the Passive Avoidance Performance test. In the Open Field test, the dementia-ridden mice and the control group performed the same, covering the same amount of ground and did not differ in locomotor activity.

There were significant differences when it came down to the passive avoidance test. While the healthy control mice were able to learn quickly to avoid the shock, the dementia mice (which were not on intervention) needed more time to learn to avoid the shock than the dementia mice that were given phosphatidylcholine.

Later on, histological analysis confirmed that the mice with dementia that received “treatment” had higher levels of choline and acetylcholine than non-treated dementia mice in the cortex and hippocampus, indicating that administration of egg phosphatidylcholine has a significant impact on neurotransmitter concentrations and memory performance for this group.

Improving Memory Impairment from Nucleus Basalis Lesion

The memory deficits observed in Alzheimer’s can be experimentally modeled by performing bilateral lesions on the nucleus basalis. One set of researchers did just this, combining lesion surgery with nutrition-focused interventions to test how behavior would be affected by various combinations of egg phosphatidylcholine and Vitamin B₁₂ supplementation.^[7]

The researchers divided the rats into several test groups, as outlined below:

sham surgery
surgery with only Vitamin B₁₂ supplementation
surgery with only egg phosphatidylcholine supplementation
surgery with both Vitamin B₁₂ and egg phosphatidylcholine supplementation

The rats, then, underwent behavioral testing (which included the Morris Water Maze). Upon completion, the rats were sacrificed, so that the scientists could get a closer look at the rats’ brains and neurotransmitter levels.

Testing revealed that the joint combination of Vitamin B₁₂ and egg phosphatidylcholine brought about the best improvement in the behaviors measured by the Morris Water Maze. Interestingly, when the rats only received Vitamin B₁₂ or only egg phosphatidylcholine, the rats did not perform better than the control group! Therefore, to see the best results in recovery, the rats needed both of the supplements.^[7]

When given both of the supplements, the rats performed at the level of the sham control group and had an acquisition time that was on par with the control group. Furthermore, rats in the dual-supplement condition spent a significantly larger amount of time in the correct quadrant of the water maze, indicating that they had better memory of the platform’s location than the rats receiving only one form of supplementation.

After the behavioral tests, biochemical analysis was performed on brain tissues. Although the sham-surgery control group exhibited the highest levels, the choline concentration levels in the frontal cortex and the hippocampus were significantly higher in the dual supplementation condition and the egg-only condition than they were in the Vitamin B₁₂ condition.

Yolkin Improves Age-Related Cognitive Deficits

Recently, Yolkin (polypeptide Y complex), a compound isolated from chicken egg yolk, has been established as a potent polypeptide with immunomodulatory properties that can reduce some cognitive deficits associated with age.^[8]

In a recent experiment ran by Lemieszewska et al., Yolkin was compared to colostrum, a mammary gland secretion which occurs during lactation and is high in proteins and peptides that are rich in proline (an amino acid which helps with development and supports the immune system).

Researchers compared Yolkin to the colostrum because colostrum has been tested in animals and in vitro and has been shown to

delay dementia and reduce aging animals’ loss of long-term memory
inhibit nerve cell apoptosis induced by the Alzheimer’s associated accumulation of toxic amyloid
improve memory and learning in rats
be effective in preliminary clinical trials on humans with Alzheimer’s disease (15 patients received the pharmaceutical approved version of colostrum known as Colostrinin at a dose of 100lg)

Thus, by comparing Yolkin to an already established, effective compound such as colostrum, there were high standards in place when running their experiments.^[8]

The experiment, involved multiple subgroups, including control group rats which were given an aqueous solution and experimental groups which were given Yolkin at 10 or 100 μg/kg of body weight (administered either orally or intraperitoneally) or Colostrinin at 50 μg/kg of body weight or Coloco-PRP at 50 μg/kg of body weight (the latter two substances were derived from bovine colostrum). The various conditions and dosage levels enabled the scientists to study exactly how the drugs would affect the animal behavior.

Several industry-standard behavioral tests were used, including the Open Field test, the Morris Water Maze, and the Novel Object Recognition test.

During the Open Field test, the rats which received Yolkin orally at a high dose (100 μg/kg of body weight) and intraperitoneally at both dosage levels (10 or 100 μg/kg of body weight) covered more distance than the placebo control group.

When it came to the Morris Water Maze test, the aged rats showed a significantly shorter distance to swim to the to target zone given higher doses of Yolkin orally. Also, when Yolkin was administered intraperitoneally, regardless of dosage level, the aged rats had a significant increase in the number of crossings made to the target zone.

Lastly, in the Novel Object Recognition test, both forms of Yolkin administration and dosage levels led to rats to have a higher preference for novel objects than the control groups did.

Given these robust findings, comparable to the behavioral effects of colostrum, Yolkin has been demonstrated to be a potent polypeptide complex with the ability to reduce age-related cognitive deficits.^[8]

Limitations and Future Directions for Research

The majority of research has focused on eggs’ chemical compounds, but in limited quantities. Instead of assessing the entire eggs’ properties in synchrony, researchers derive the egg white (or just the yolk or certain proteins found within the egg white) and conduct their experiments using a small fraction of the egg. Thus, the entire egg profile is infrequently used in research settings and future research needs to be conducted to address such a limitation.

Another limitation includes the use of human subjects. For example, current reviews and studies with the scope of understanding how an egg-filled diet affects inflammation in different human populations (ranging from healthy to obese) involve dietary protocols that require eating 2-4 eggs daily for the span of consecutive 4 weeks or more, without any breaks.

Not surprisingly, after eating 4 eggs a day for 4 weeks straight, human subjects demonstrated an increase in inflammatory markers.^[1] Little is known about how eating eggs occasionally (about 2 times per week) impacts health and cognition (a consumption pattern that is much more popular and likely).

Conclusion

Although much has been established about eggs, including the effect of certain bioactive compounds on behavioral profiles, there are still many gaps and holes that need to be filled.

For example, a certain class of lipids (unsaturated fats and polyunsaturated fats) have been established as being quite beneficial for the brain, given the brain’s own high-fat content, having the ability to ward off the cognitive decline associated with Alzheimer’s.

However, little is known about how the egg’s unique mixture of monounsaturated fats and saturated fats can affect brain health and performance.^[9] Even less is known about how eggs interact with other compounds such as vitamins. The case study mentioned previously involving lesioning of the nucleus basalis and the cognitive benefits brought about by dual supplementation of Vitamin B₁₂ and egg phosphatidylcholine is an exception, thus more research needs to be done on eggs’ synergistic effects with other compounds. Therefore, more studies are needed to identify the synergetic effects between egg compounds and other bioactive compounds.

Behaviors that have already been somewhat addressed by research include anxiety and hypertension, memory, and learning. Given the egg’s dynamic profile, filled with proteins, fats, and lipids, there is much promise for future research and it is probably just a matter of time until more significant findings are added to this list.

References

Andersen, Catherine J. “Bioactive egg components and inflammation.” Nutrients 7.9 (2015): 7889-7913.
Fujita, Hiroyuki, Ryuzo Sasaki, and Masaaki Yoshikawa. “Potentiation of the antihypertensive activity of orally administered ovokinin, a vasorelaxing peptide derived from ovalbumin, by emulsification in egg phosphatidylcholine.” Bioscience, biotechnology, and biochemistry 59.12 (1995): 2344-2345.
Ishiguro, Koji, et al. “Hypotensive effect of a sweetpotato protein digest in spontaneously hypertensive rats and purification of angiotensin I-converting enzyme inhibitory peptides.” Food chemistry 131.3 (2012): 774-779.
Ruiz-Giménez, Pedro, et al. “Antihypertensive effect of a bovine lactoferrin pepsin hydrolysate: identification of novel active peptides.” Food Chemistry 131.1 (2012): 266-273.
Yu, Zhipeng, et al. “Anxiolytic effects of ACE inhibitory peptides on the behavior of rats in an elevated plus-maze.” Food & function 7.1 (2016): 491-497.
Chung, Shu-Ying, et al. “Administration of phosphatidylcholine increases brain acetylcholine concentration and improves memory in mice with dementia.” The Journal of nutrition 125.6 (1995): 1484-1489.
Masuda, Y., et al. “Egg phosphatidylcholine combined with vitamin B12 improved memory impairment following lesioning of nucleus basalis in rats.” Life sciences 62.9 (1998): 813-822.
Lemieszewska, Marta, et al. “Pro-cognitive properties of the immunomodulatory polypeptide complex, yolkin, from chicken egg yolk and colostrum-derived substances: Analyses based on animal model of age-related cognitive deficits.” Archivum immunologiae et therapiae experimentalis 64.5 (2016): 425-434.
Morris, Martha C. “Nutritional determinants of cognitive aging and dementia.” Proceedings of the Nutrition Society 71.1 (2012): 1-13.