All you need to know about egg yolk

Egg yolks used to have a bad reputation because of their high-cholesterol content. Doctors and health authorities once recommended that people limit egg yolk consumption, especially individuals with high cholesterol, blood pressure, or heart conditions.

But more focused research indicates that high blood levels of cholesterol are less influenced by cholesterol-containing foods, such as eggs, than individual factors, such as ethnicity, gender, hormonal functioning, and overall nutrition.

Like egg whites, egg yolks have a high protein content and contain many essential vitamins, minerals, fats, and healthy calories.

Fast facts on egg yolk nutrition:

• Nutrients vary between eggs naturally.
• Most research shows that egg yolks contain most of the nutrition found in eggs.
• Like most animal-sourced foods, eggs carry some potential health risks.

What are the benefits

Studies suggest that eggs may play a role in healthy eating patterns.

Eggs are a low-cost, nutrient-filled, easy to access and prepare food, making them an excellent dietary staple for many people worldwide. Eggs are also a very versatile food. And the consumption of eggs does not usually conflict with most religious or moral guidelines.

Eating egg whites and yolks together in a whole egg also contains the right balance of protein, fat, and calories that allows most people to feel fuller and more satisfied at meals.

A 2015 study found that obese Mexican-American women who ate eggs regularly after pregnancy got higher overall scores on the Healthy Eating Index than those who did not, suggesting eggs might play a role in healthy eating patterns.

Possible further health benefits associated with egg yolks include:

• increasing immune function, including antioxidant, antimicrobial, and anti-cancer action
• increasing eye health, including lowering the risk of macular degeneration, and age-related cataracts
• improving bone density and resilience
• maintaining a healthy blood production and composition, especially iron content and clotting factors
• maintaining a healthy, regulated metabolism
• improving fat and protein metabolism
• improving cellular growth and repair
• improving cardiovascular health
• maintaining a healthy blood pressure
• increasing skin and hair health
• improving bowel and bladder health
• increasing nutritional absorption during digestion
• production and health of neurotransmitters
• improved brain development and health
• reducing the risk of bowel obstruction and kidney stones
• reducing overall body inflammation

More recently researchers have begun to explore the potential of various immune-stimulating compounds found in egg yolks called immunoglobulins.

A 2017 study found that female mice that consumed the egg yolk nutrient anti-VacA IgY were less likely to get become infected by Helicobacter pylori, a bacteria that commonly causes intestinal infection.

Nutrition

The amount of nutrition in each egg yolk depends on the size of the egg, how it was raised and processed, and what species it is. And the final dietary value of egg yolks varies greatly depending on how they are prepared. For example, cooking whole eggs in oil may double, even triple, the fat and cholesterol content of an egg dish.

According to the United States Department of Agriculture (USDA), a raw egg yolk from one standard, large (17 gram) egg in the United States has:

• 55 calories
• 2.7 grams(g) protein
• 4.51 g fat: 1.624 g saturated fat, 1.995 g monounsaturated fat, and 0.715 g of polyunsaturated fat
• 184 milligrams (mg) of cholesterol
• 0.61 g of carbohydrate
• 0.10 g of sugar
• 0 g dietary fiber

Egg yolks contain at least seven essential minerals, including:

• 22 mg calcium
• 0.46 mg iron
• 1 mg magnesium
• 66 mg phosphorus
• 19 mg potassium
• 8 mg sodium
• 0.39 mg zinc

Egg yolks are high in many vitamins, especially fat and water-soluble vitamins.

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The table below outlines the vitamin content of one large (17 g) egg yolk.

Thiamin	0.030 mg
Riboflavin	0.090 mg
Niacin	0.004 mg
Vitamin B-6	0.059 mg
Vitamin B-9 (folate)	25 microgram (µg)
Vitamin B-12	0.33 µg
Vitamin A, RAE	65 µg
Vitamin A, IU	245 international units (IU)
Vitamin E	0.44 mg
Vitamin D (D2 and D3)	0.9 µg
Vitamin D	37 IU
Vitamin K	0.1 µg

Egg yolks are also high in many compounds, vitamins, and other nutrients known to have health benefits, including the prevention of several long-term and infectious diseases.

Per unit size, duck, quail, and free-range heritage hen eggs are considered to contain higher amounts of most of the important nutrients than conventional chicken eggs.

Yolk vs. egg white

Contact with raw egg means hands and surfaces should be washed.

Egg yolks contain an average of 43 percent of the total protein content of the egg.

And nearly all the water-soluble and fat-soluble vitamins and minerals in eggs are found in the yolk. Several studies have concluded that consuming whole eggs has far more significant benefits than eating egg whites alone.

For example, a 2017 study found that young men who ate whole eggs immediately after resistance exercises had higher rates of muscular metabolism than those who only consumed egg whites.

The fact that most of an egg's nutrition is found in its yolk should not be surprising. Biologically, egg yolks are designed to be the primary source of nutrients for a growing embryo.

Eating egg yolks safely

The most common health concern associated with eggs is food poisoning from the bacteria Salmonella. Poultry naturally carry Salmonella and can contaminate their eggs with the bacteria.

Salmonella infections can be very serious, especially for young children, people with immune conditions, and those over the age of 65. But following a few basic safety precautions when purchasing, storing, handling, and cooking eggs significantly reduces the risk of Salmonella poisoning.

Tips for safely dealing with eggs include:

• purchasing eggs from a reputable, licensed source or a trusted local farmer
• making sure eggs are not cracked, have holes, or are dirty before purchasing
• always storing eggs in the refrigerator at 40°F (4°C) and making sure they are refrigerated before purchase
• washing hands and all exposed surfaces with soap and water immediately after coming into contact with raw eggs
• eating or refrigerate eggs shortly after cooking them, no more than 2 hours
• cooking eggs until at least the whites are firm — for high-risk individuals, cook eggs until both the whites and yolk are firm
• cooking egg dishes, such as casseroles or quiches, to an internal temperature of at least 160°F (71°C) — if unsure about egg temperatures while cooking, use a cooking thermometer
• cooking scrambled eggs until firm
• throwing away broken, dirty, or cracked eggs
• throwing away expired eggs and egg products
• avoiding eggs that have an odd consistency, appearance, or smell
• keeping raw eggs away from other foods, especially those consumed raw
• using pasteurized eggs for dressings and condiments that require soft-boiled eggs, such as Hollandaise sauce, mayonnaise, and Cesar salad dressing

In general, the link between egg yolks and chronic conditions, such as cardiovascular disease, high-cholesterol, high-blood pressure, and disorders that influence circulation, such as diabetes, remains unclear.