The bottom line, says Marion Nestle, author of What to Eat and the Paulette Goddard Professor of Nutrition, Food Studies, and Public Health at New York University, is that “the color [of an egg yolk] doesn’t reflect the nutrient value in any significant way.”
Egg yolks range in color from pale yellow to deep orange. Richer-colored egg yolks are more likely to come from free-range hens, says Dr. Hilary Shallo Thesmar, director of food safety programs for the Egg Nutrition Center (ENC): Free-range hens have the opportunity to eat more pigmented foods, and the pigment is then transferred to the yolk. But the macronutrients (protein and fat) remain the same regardless of yolk color, Thesmar says. “However, there might be small changes in some of the micronutrients such as vitamin A and/or lutein.”
Nestle explains that the color of a yolk is due specifically to carotenoids, which are natural pigments found in some plants. Some carotenoids, like beta-carotene, have nutritional value (our bodies convert beta-carotene into vitamin A, for instance). But deeper-colored egg yolks only indicate the presence of carotenoids in general, says Nestle, not necessarily the presence of beta-carotene. And other carotenoids that might be present “may have antioxidant function, but they are not essential nutrients,” she says.
While the yolk is not an indicator of nutritive value, there is mounting evidence that true pasture-raised hens produce more nutritious eggs overall. The ENC, however, states that “free-range eggs do not differ from regular eggs in terms of nutritional value or cholesterol level.”