Macro and Micro-Nutrient in Eggs

Eggs have been a staple in the human diet for				egg iron bioavailability. In addition to iron, eggs contain
thousands of years. From hunter-gatherers collecting				calcium, phosphorus, sodium, potassium, magnesium,
eggs from the nests of wild birds, to the				zinc, copper, and manganese. Egg yolks also contain
domestication of fowl for more reliable access to a				iodine (25 mg per large egg), and this can be
supply of eggs, to today's genetically selected birds				increased twofold to threefold by the inclusion of an
and modern production facilities, eggs have long been				iodine source in the feed. Egg selenium content can
recognized as a source of high-quality protein and				also be increased up to ninefold by dietary
other important nutrients.				manipulations.
Over the years, eggs have become an essential				Egg Choline
ingredient in many cuisines, owing to their many				Choline was established as an essential nutrient in
functional properties, such as water holding,				1999 with recommended daily intakes (RDIs) of
emulsifying, and foaming. An egg is a self-contained				550mg for men and 450mg for women. The RDI for
and self-sufficient embryonic development chamber.				choline increases during pregnancy and lactation owing
At adequate temperature, the developing embryo				to the high rate of choline transfer from the mother
uses the extensive range of essential nutrients in the				to the fetus and into breast milk. Animal studies
egg for its growth and development. The necessary				indicate that choline plays an essential role in brain
proteins, lipids, carbohydrates, vitamins, minerals, and				development, especially in the development of the
functional nutrients are all present in sufficient				memory centers of the fetus and newborn. Egg-yolk
quantities for the transition from fertilized cell to				lecithin (phosphatidylcholine) is an excellent source of
newborn chick, and the nutrient needs of an avian				dietary choline, providing 125mg of choline per large
species are similar enough to human needs to make				egg.
eggs an ideal source of nutrients for us. (The one				Egg Carotenes
essential human nutrient that eggs do not contain is				Egg yolk contains two xanthophylls (carotenes that
ascorbic acid (vitamin C), because non-passerine birds				contain an alcohol group) that have important health
have active gulonolactone oxidase and synthesize				benefits - lutein and zeaxanthin. It is estimated that a
ascorbic acid as needed.) This article summarizes the				large egg contains 0.33 mg of lutein and zeaxanthin;
varied nutrient contributions eggs make to the human				however, the content of these xanthophylls is totally
diet.				dependent on the type of feed provided to the
Macro and Micro Nutrient in Eggs				hens. Egg-yolk lutein levels can be increased up to
The levels of many nutrients in an egg are influenced				tenfold through modification of the feed with
by the age and breed or strain of hen as well as the				marigold extract or purified lutein.
season of the year and the composition of the feed				An indicator of the luteinþzeaxanthin content is the
provided to the hen. While most variations in				color of the yolk; the darker yellow-orange the yolk,
nutrients are relatively minor, the fatty acid				the higher the xanthophyll content. Studies have
composition of egg lipids can be significantly altered				shown that egg-yolk xanthophylls have a higher
by changes in the hen's diet. The exact quantities of				bioavailablity than those from plant sources, probably
many vitamins and minerals in an egg are determined,				because the lipid matrix of the egg yolk facilitates
in part, by the nutrients provided in the hen's diet.				greater absorption. This increased bioavailability results
Hen eggs contain 75.8% water, 12.6% protein, 9.9%				in significant increases in plasma levels of lutein and
lipid, and 1.7% vitamins, minerals, and a small amount				zeaxanthin as well as increased macular pigment
of carbohydrates. Eggs are classified in the protein				densities with egg feeding.
food group, and egg protein is one of the highest				Egg Cholesterol
quality proteins available. Virtually all lipids found in				Eggs are one of the richest sources of dietary
eggs are contained in the yolk, along with most of				cholesterol, providing 215 mg per large egg. In the
the vitamins and minerals. Of the small amount of				1960s and 1970s the simplistic view that dietary
carbohydrate (less than 1% by weight), half is found				cholesterol equals blood cholesterol resulted in the
in the form of glycoprotein and the remainder as				belief that eggs were a major contributor to
free glucose.				hypercholesterolemia and the associated risk of
Egg Protein				cardiovascular disease. While there remains some
Egg proteins, which are distributed in both yolk and				controversy regarding the role of dietary cholesterol
white (albumen), are nutritionally complete proteins				in determining blood cholesterol levels, the majority of
containing all the essential amino-acids (EAA). Egg				studies have shown that saturated fat, not dietary
protein has a chemical score (EAA level in a protein				cholesterol, is the major dietary determinant of
food divided by the level found in an 'ideal' protein				plasma cholesterol levels (and eggs contain 1.5 g of
food) of 100, a biological value (a measure of how				saturated fat) and that neither dietary cholesterol nor
efficiently dietary protein is turned into body tissue)				egg consumption are significantly related to the
of 94, and the highest protein efficiency ratio (ratio				incidence of cardiovascular disease. Across cultures,
of weight gain to protein ingested in young rats) of				those countries with the highest egg consumption
any dietary protein. The major proteins found in egg				actually have the lowest rates of mortality from
yolk include low density lipoprotein (LDL), which				cardiovascular disease, and within-population studies
constitutes 65%, high density lipoprotein (HDL),				have not shown a correlation between egg intake
phosvitin, and livetin. These proteins exist in a				and either plasma cholesterol levels or the incidence
homogeneously emulsified fluid. Egg white is made up				of heart disease. A 1999 study of over 117 000 men
of some 40 different kinds of proteins. Ovalbumin is				and women followed for 8-14 years showed that the
the major protein (54%) along with ovotransferrin				risk of coronary heart disease was the same
(12%) and ovomucoid (11%). Other proteins of				whether the study subjects consumed less than one
interest include flavoprotein, which binds riboflavin,				egg a week or more than one egg a day. Clinical
avidin, which can bind and inactivate biotin, and				studies show that dietary cholesterol does have a
lysozyme, which has lytic action against bacteria.				small influence on plasma cholesterol levels. Adding
Egg Lipids				one egg per day to the diet would, on average,
A large egg yolk contains 4.5 g of lipid, consisting of				increase plasma total cholesterol levels by
triacylglycerides (65%), phospholipids (31%), and				approximately 5mg dl_1 (0.13mmol/L). It is important
cholesterol (4%). Of the total phospholipids,				to note, however, that the increase occurs in both
phosphatidylcholine (lecithin) is the largest fraction and				the atherogenic LDL cholesterol fraction (4mg
accounts for 26%. Phosphatidylethanolamine				dl_1(0.10mmol/L)) and the antiatherogenic HDL
contributes another 4%. The fatty-acid composition				cholesterol fraction (1 mg dl_1(0.03mmol/L)), resulting
of eggyolk lipids depends on the fatty-acid profile of				in virtually no change in the LDL:HDL ratio, a major
the diet. The reported fatty-acid profile of				determinant of cardiovascular disease risk. The
commercial eggs indicates that a large egg contains				plasma lipoprotein cholesterol response to egg
1.55 g of saturated fatty acids, 1.91 g of				feeding, especially any changes in the LDL:HDL ratio,
monounsaturated fat, and 0.68 g of polyunsaturated				vary according to the individual and the baseline
fatty acids. (Total fatty acids (4.14 g) does not equal				plasma lipoprotein cholesterol profile. Adding one egg
total lipid (4.5 g) because of the glycerol moiety of				a day to the diets of three hypothetical patients with
triacylglycerides and phospholipids and the				different plasma lipid profiles results in very different
phosphorylated moieties of the phospholipids). It has				effects on the LDL:HDL ratio. For the individual at low
been reported that eggs contain less than 0.05 g of				risk there is a greater effect than for the person at
trans-fatty acids. Egg yolks also contain cholesterol				high risk, yet in all cases the effect is quantitatively
(211mg per large egg) and the xanthophylls lutein and				minor and would have little impact on their
zeaxanthin.				heart-disease risk profile.
Egg Vitamins				Overall, results from clinical studies indicate that egg
Eggs contain all the essential vitamins except vitamin				feeding has little if any effect on cardiovascular
C, because the developing chick does not have a				disease risk. This is consistent with the results from a
dietary requirement for this vitamin. The yolk				number of epidemiological studies. A common
contains the majority of the water-soluble vitamins				consumer misperception is that eggs from some
and 100% of the fat-soluble vitamins. Riboflavin and				breeds of bird have low or no cholesterol. For
niacin are concentrated in the albumen. The riboflavin				example, eggs from Araucana chickens, a South
in the egg albumin is bound to flavoprotein in a 1:1				American breed that lays a blue-green egg, have
molar ratio. Eggs are one of the few natural sources				been promoted as low-cholesterol eggs when, in fact,
of vitamins D and B12. Egg vitamin E levels can be				the cholesterol content of these eggs is 25% higher
increased up to tenfold through dietary changes.				than that of commercial eggs. The amount of
While no single vitamin is found in very high quantity				cholesterol in an egg is set by the developmental
relative to its DRI value, it is the wide spectrum of				needs of the embryo and has proven very difficult
vitamins present that makes eggs nutritionally rich.				to change substantially without resorting to
Egg Minerals				hypocholesterolemic drug usage. Undue concerns
Eggs contain small amounts of all the minerals				regarding egg cholesterol content resulted in a steady
essential for life. Of particular importance is the iron				decline in egg consumption during the 1970s, 1980s,
found in egg yolks. Research evaluating the plasma				and early 1990s, and restriction of this important and
iron and transferrin saturation in 6-12-month-old				affordable source of high-quality protein and other
children indicated that infants who ate egg yolks had				nutrients could have had negative effects on the
a better iron status than infants who did not. The				well-being of many nutritionally 'at risk' populations. Per
study indicated that egg yolks can be a source of				capita egg consumption has been increasing over the
iron in a weaning diet for breast-fed and formula-fed				past decade in North America, Central America, and
infants without increasing blood antibodies to egg-yolk				Asia, has remained relatively steady in South America
proteins. Dietary iron absorption from a specific food				and Africa, and has been falling in Europe and
is determined by iron status, heme- and				Oceania. Overall, world per capita egg consumption
nonheme-iron contents, and amounts of various				has been slowly increasing over the past decade, in
dietary factors that influence iron absorption present				part owing to the change in attitude regarding dietary
in the whole meal. Limited information is available				cholesterol health concerns.
about the net effect of these factors as related to

ClinTrial

Macro and Micro-Nutrient in Eggs