Nurturing The Brain – Part 4, Eggsby Sara Adaes, PhD | May 17, 2015
We have been witnessing the ascent of eggs as nutritional superstars. For many years, eggs suffered from a fairly bad reputation mainly because of their high cholesterol content.
The classical notion was that dietary cholesterol was associated with increased risk for coronary heart disease (CHD) and stroke, and this was the premise for dietary recommendations in the US defining a dose of no more than 300 mg/day of cholesterol for healthy populations – less than the amount provided by two eggs. But it turns out that this was quite a scrambled notion.
Recent studies have challenged this view and have shown that dietary cholesterol has little or no effect on the blood cholesterol levels of most people and is therefore not correlated with increased risk for CHD in the healthy population (although it can be in individuals with specific sensitivities to dietary cholesterol). Dietary cholesterol actually stimulates HDL cholesterol production (the good one), decreasing the LDL/HDL cholesterol ratio. A study evaluating the effect of a daily consumption of two eggs during 6 weeks showed that HDL levels can increase by 10%. People who have higher levels of HDL usually have a decreased risk of CHD, stroke and other health problems.
In fact, in most countries, namely in European countries, dietary guidelines do not place restrictions on dietary cholesterol intake. Likewise, the US’s Dietary Guidelines Advisory Committee (DGAC) has now dropped dietary cholesterol restrictions. By the way, they have also recommended cutting back on salt, sugar and saturated fat, and adopting a healthier, Mediterranean-like dietary pattern that includes fruits, vegetables, nuts, whole grains, fish and moderate levels of alcohol (for adults); read it here.
So, now that we know that dietary cholesterol is not a monster, the coast is clear for eggs. And this is great, since eggs are incredibly packed with antioxidants, vitamins, proteins, omega-3 fatty acids, and many other nutrients. Many of the nutrients that the DGAC found to be underconsumed in the US population are actually present in eggs, like for example, vitamin A, vitamin D, vitamin E, folate, and calcium.
The health benefits of eggs
As mentioned, eggs can help lower the risk of cardiovascular disease and stroke by increasing HDL and lowering LDL. Eggs have also been found to improve insulin sensitivity, thereby lowering the risk of diabetes. There are also clear benefits from consuming adequate amounts of vitamins, proteins and vitamins in the overall health. But there are other interesting health effects associated with other less obvious nutrients which are present in eggs, namely choline, lutein and zeaxanthin.
Lutein and zeaxanthin are carotenoids with major antioxidant properties. An impressive fact is that, of the hundreds of carotenoids found in nature, only two can accumulate in high quantities in the retina in the eye and they are both found in eggs (and green vegetables): lutein and zeaxanthin, precisely. These molecules can filter and protect cells from harmful high-energy blue wavelengths of light.
Many studies have shown that daily intake of lutein and zeaxanthin can reduce the risk of chronic eye diseases, specifically of age-related macular degeneration (AMD) and cataracts. These are very common eye disorders: AMD is the leading cause of blindness in older adults in the Western world and its incidence keeps increasing.
Egg yolks contain large amounts of both lutein and zeaxanthin. According to a controlled trial assessing the effect of egg consumption on the plasma levels of both molecules, eating an average of just 1.3 egg yolks per day for 4.5 weeks increased blood levels of lutein by 28% and of zeaxanthin by 142%. As a bonus, the high amount of Vitamin A in eggs also helps keep your eyes healthy.
Choline is another amazing nutrient found in eggs. Choline is officially recognized as an essential nutrient. It has numerous complex functions in the body, particularly in the brain, where it is needed for the synthesis of an important neurotransmitter, acetylcholine. Choline is required to make phospholipids that are essential components of cellular membranes. It is also involved, either directly or indirectly, in metabolic regulation and detoxification in the body.
Studies have shown that brain development and memory may be enhanced by the choline content of eggs. Indeed, choline supplementation during critical periods of neonatal development has been shown to have long-term beneficial effects on memory. Also, choline is essential in decreasing the risk of occurrence of neural tube defects, i.e, malformations of the brain, spine, or spinal cord, such as spina bifida, for example.
Choline is essential during embryonary brain development and throughout life. Choline deficits have huge health consequences that can lead to severe organ dysfunctions. Choline is also essential for cardiovascular and brain function and has been shown to reduce inflammation and have beneficial effects in diabetes, Alzheimers, and other diseases. Choline is extremely important and egg yolks are actually the most concentrated source of this molecule in diet.
So, there you have it: eggs are great.
Bonus: one additional benefit from eggs is that they are extremely fulfilling, mostly due to their high protein content; they help reduce food intake by maintaining satiety for longer periods of time, which in the long run may actually lead to weight loss.
Blesso CN, Andersen CJ, Barona J, Volek JS, & Fernandez ML (2013). Whole egg consumption improves lipoprotein profiles and insulin sensitivity to a greater extent than yolk-free egg substitute in individuals with metabolic syndrome. Metabolism: clinical and experimental, 62 (3), 400-10 PMID: 23021013
Delcourt C, Carrière I, Delage M, Barberger-Gateau P, Schalch W, & POLA Study Group (2006). Plasma lutein and zeaxanthin and other carotenoids as modifiable risk factors for age-related maculopathy and cataract: the POLA Study. Investigative ophthalmology & visual science, 47 (6), 2329-35 PMID: 16723441
Fernandez ML (2006). Dietary cholesterol provided by eggs and plasma lipoproteins in healthy populations. Current opinion in clinical nutrition and metabolic care, 9 (1), 8-12 PMID: 16340654
Fernandez ML (2012). Rethinking dietary cholesterol. Current opinion in clinical nutrition and metabolic care, 15 (2), 117-21 PMID: 22037012
Handelman GJ, Nightingale ZD, Lichtenstein AH, Schaefer EJ, & Blumberg JB (1999). Lutein and zeaxanthin concentrations in plasma after dietary supplementation with egg yolk. The American journal of clinical nutrition, 70 (2), 247-51 PMID: 10426702
Zeisel SH, & da Costa KA (2009). Choline: an essential nutrient for public health. Nutrition reviews, 67 (11), 615-23 PMID: 19906248
Zeisel SH (2006). Choline: critical role during fetal development and dietary requirements in adults. Annual review of nutrition, 26, 229-50 PMID: 16848706
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