The egg white and its sunny golden yolk each have their own intrinsic nutritional value. The lower-calorie, cholesterol-free white contains much of the egg's protein, while the yolk is the egg's proprietary source of choline, lutein and zeaxanthin. If you use only egg whites in meals and in cooking, you can indeed end up with heart healthier food. However, you also part ways with the most nutritious part of the egg, which is the yolk.
Whole Egg
According to the Egg Nutrition Center, a single whole egg gives you 6.3 g of protein, 0.4 g of carbohydrates and 5.0 g of fat and cholesterol. An egg white contains only 16 calories, while the yolk bears the brunt of the caloric burden, at 54 calories. An egg white contains 3.6 g of protein compared to the yolk's 2.7 g. Egg whites are heart healthier, containing none of the egg's fat or cholesterol. The egg yolk contains all of the egg's cholesterol, around 210 g.
Vitamins
From a nutritional standpoint, the egg white may seem healthier because it has no fat or cholesterol, and substantially fewer calories. However, it's also bereft of many essential vitamins, containing only nominal amounts of folate, vitamin B12 and riboflavin, according to the Egg Nutrition Center. The yolk is far richer in vitamins, containing 245 IU of vitamin A, 18 IU of vitamin D, 0.44 mg of vitamin E, 25 mcg of folate and 116 mcg of choline. Choline is a nutrient that's been linked to memory, according to the Harvard Medical School.
Minerals
The egg white and yolk both contain vital nutrients in varying amounts. Egg yolks take the lead in calcium, phosphorous and selenium. The yolk has 22 mg of calcium compared to the white's 2 mg, and 66 mg phosphorous to the white's 5 mg. Egg yolks contain 9.5 mcg selenium, while the white contains 6.6. However, the egg white tops the yolk in potassium and magnesium, containing 54 and 4 mg, respectively, to the yolk's 19 and 1 mg. The egg's sodium content -- a count to keep track of if you're watching your sodium consumption -- is found mainly in the white, which contains 55 mg compared to the yolk's 8 mg.
Other Yolk Benefits
Egg yolks also contain minute amounts of the cartenoids lutein and zeaxanthin, around 186 mcg per yolk. According to the American Egg Board, these nutrients encourage good eye health, preventing blindness related to old age.
Eggs and Health
Eggs have a bad reputation as an artery clogger because of their cholesterol content, and the Harvard Medical School concedes that the yolk's cholesterol count is fairly impressive, on par with that found in liver, duck and shrimp. However, not all of the dietary cholesterol you consume makes a beeline for your arteries; only a tiny amount of it finds its way into your blood. Saturated and trans fats have more of an impact on your blood cholesterol levels. One egg a day is part of a healthy diet, as long as you're keeping an eye on the amount of saturated and trans fats you consume.
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