Shoppers picking between brown and white eggs at supermarkets often assume shell colour signals nutritional value, but experts say the belief has no scientific basis.
According to the United States Department of Agriculture (USDA), shell colour depends on the breed of hen, not on the egg's nutritional content. Leghorn, White Rock and Cornish hens lay white eggs, while Rhode Island Red, New Hampshire and Plymouth Rock hens lay brown eggs. Araucana hens, native to South America, lay eggs that are blue or green.
The colour difference comes down to pigmentation. Brown eggshells get their colour from protoporphyrin IX, a compound derived from blood haem, while blue eggs carry a different pigment called biliverdin. A 2015 review found that pigment levels in brown eggs can also vary with a hen's age, strain, housing conditions, certain diseases, and stress.
The USDA states that nutrient levels are not significantly different between white and brown shell eggs. Claims that blue or green eggs from Araucana hens contain less cholesterol than other eggs have also not been proven by research.
Egg size, however, does affect nutritional content regardless of colour. The USDA's Certified Egg Facts note that jumbo eggs contain approximately 90 calories and 8 grams of protein, compared to 60 calories and 6 grams of protein in medium eggs.
Shell colour also has little bearing on taste. Freshness, the hen's diet, and cooking method have a far greater effect on flavour than the colour of the shell.
What does affect nutritional value is how the hen is raised. Hens with access to sunlight and open-air movement may produce eggs with higher vitamin D content than those raised in cages.
Enriching a hen's feed with omega-3-rich ingredients such as flaxseed can increase the omega-3 fatty acid content of its eggs, and adding vitamin-rich feed can raise specific vitamin levels as well.
Brown eggs have historically carried a higher price, partly because brown-egg-laying breeds were traditionally larger birds that consumed more feed and, in some cases, produced fewer eggs, raising production costs.
Although production methods have since changed, the perception that brown eggs are more nutritious — along with the fact that many organic and free-range eggs happen to be brown — continues to keep their market price higher.
Nutritionists recommend that shoppers focus less on shell colour and more on freshness, storage conditions, and what the hen was fed when choosing eggs.
There is no scientific basis for the belief that brown eggs are more nutritious than white ones.v
