The egg yolk has a very different nutritional profile from the egg white. Even though the yolk tends to be higher in vitamins and minerals, it's also higher in unhealthy fats and cholesterol. For some people, consuming only the white part of the egg may be a better option for health.
Calories in the Yolk and White
Because egg whites are virtually fat free, they're much lower in overall calories, providing about two-thirds fewer calories. A single egg yolk from a large egg has 55 calories. But if you separate the yolk and eat only the egg white from that large egg, you'll get around 17 calories.
Protein of the Yolk and White
Both the yolk and the white are relatively comparable as far as protein content. A large egg yolk gives you 2.7 grams of protein, while the white part provides approximately 3.6 protein grams. Either way, you're getting less than 3 percent of your protein requirement for a 2,000-calorie diet. You should be getting 10 to 35 percent of your calories from protein, which has 4 calories per gram, according to the Dietary Guidelines for Americans 2010. If 2,000 calories a day is your average, 50 to 175 grams of protein should be your daily goal.
An egg yolk from a large egg contains around 4.5 grams of total fat. This is nearly 99 percent more fat than the white part, which has a mere 0.06 gram of total fat. Don't be afraid of having fat in your diet, because it has all kinds of functions, from making hormones to absorbing vitamins. Between 20 and 35 percent of the calories in your diet ideally should come from fat. Because you'll get 9 calories from a gram of fat, this amounts to 44 to 78 grams for a 2,000-calorie diet.
Eggs are a rich source of vitamin B-12, which is a nutrient that is essential for your metabolism and for healthy blood cells. Much of that B-12, though, is found in the yolk. You'll get more than 0.3 micrograms of the vitamin from a large egg yolk and just 0.03 micrograms from the white. Since all adults need 2.4 micrograms daily, according to the Food and Nutrition Board at the Institute of Medicine, that yolk has more than 12 percent of your B-12 needs for the day.
You'll get 8 to 10 percent of your vitamin A needs for the day from a yolk, but the white supplies you with no vitamin A, which is a nutrient you need for optimal vision. That same yolk even has nearly 10 percent of your vitamin D requirement to keep your bones strong. Egg whites do not contain vitamin D. A large egg yolk helps you get more than 21 percent of the choline your body requires daily. Choline is vital for nerve and brain function. You'll get less than 1 percent of your choline recommendation from a large egg white.
Both the yolk and the white are full of selenium. You need selenium to protect all your cells; selenium gets rid of damaging free radicals that increase your risk of developing chronic diseases. The yolk has 17 percent of your daily needs, while the white has 12 percent. To help keep your bones strong, an egg yolk gives you nearly 10 percent of your recommended phosphorus. The egg white, on the other hand, has less than 1 percent.
If you have a risk of developing heart disease, have high cholesterol or if your blood pressure runs high, you'll probably want to stay away from egg yolks. All of the 1.6 grams of saturated fat in eggs comes from the yolk. Because saturated fat should make up no more than 10 percent of your calories, the Dietary Guidelines for Americans 2010 states that you need to limit yourself to 22 grams a day, maximum, for a 2,000-calorie diet. A single egg yolk takes up more than 7 percent of that amount. Yolks are full of cholesterol, too. You'll get close to 185 milligrams of cholesterol from a yolk, which is more than 60 percent of your 300 milligram daily allowance. Whites do not contain cholesterol.