Science Can Explain Why Certain Eggs Are More Nutritious Than Others

When it comes to foods that pack a lot of nutrients in a small serving, eggs are arguably one of the top selections. One large egg contains about 6 grams of protein, and is also considered a good source of B vitamins, choline, vitamin D, and iodine. But if you've shopped for eggs lately, you might have noticed different egg carton labels promising different types of nutrients. You're likely wondering: Why are some eggs advertised as being more nutritious than others? The scientific explanation for such differences boils down to the nutrients hens consume before they lay eggs, which is also related to varying farming practices.

Most chicken eggs contain the same basic nutrients, yet it's also true that some types of eggs offer a bit more than others, particularly vitamin D and omega-3 fatty acids. The explanation for this variation is the diet that hens are fed on different farms. First, all eggs contain vitamin D (a nutrient that might slow down aging) in their yolks. Some of this may be attributed to UVB exposure from the sun among hens that are able to go outdoors. A 2020 review in Trends in Food Science & Technology also noted that many eggs are fortified with vitamin D, via vitamin D3 in chicken feed. 

Some farmers may also intentionally increase omega-3 fatty acids in a hen's diet by giving them fish oil or flaxseeds. According to Columbia University Irving Medical Center, such practices can increase the omega-3 content of an average egg from 30 milligrams to between 100 and 600 milligrams each! It's also possible that hens who are allowed to forage on grasses may end up consuming more omega-3s.

It's important to understand the differences between pasture-raised, free-range, and cage-free eggs, and how these might possibly impact their nutrition. You might have come across these labels on various egg carton brands, and have wondered if these impact overall egg nutrition. While the answer is not yet definitive due to nuances in their living environments, some researchers believe it's possible that hens who spend more time outdoors may end up laying more nutritious eggs. This has to do with more access to different food sources outside, where they can naturally feed on grasses and bugs they find, not just the grains fed to them.

Overall, pasture-raised hens are given much more freedom to roam around. Eggs that are pasture-raised generally come from hens who have at least 108 square feet of space to walk around and forage. In theory, pasture-raised hens can have the capability to lay more nutritious eggs because they ultimately have access to more nutrients compared to their indoor counterparts. On the flipside, the terms "free-range" and "cage-free" may be feel a bit misleading to some consumers. Free-range eggs come from hens that are technically given at least 2 square feet of space to roam, which is far less than pasture-raised hens. Also, not all free-range chickens go outside every day. Cage-free eggs come from hens who can move freely indoors, but they may not have access to the outdoors where they can naturally forage on other nutrient-rich foods.

While it makes sense that hens with more varied diets from outdoor foraging might lay more nutritious eggs, there's still some debate on this point. Unless the hens are fed supplements, their living conditions do not automatically mean pasture-raised or free-range versions will definitively lay more nutritious eggs. The problem is that it's impossible to know exactly how many additional nutrients egg-laying hens might consume outdoors when foraging on their own. So rather than fixating on farming practices indicated on egg cartons alone, you might instead rely on careful readings of nutrition labels. This can help you compare which brands might have more vitamin D and omega-3 fatty acids than others.

Aside from nutrition though, product labels on egg cartons do point to the types of conditions the hens are ultimately raised in, and possibly even point to the ecological impacts of chicken farming. For many people, pasture-raised and free-range varieties match their personal ethics around eating chicken eggs because the hens are raised in more humane conditions. Yet it's also worth mentioning that pasture-raised eggs tend to be among the more expensive types of eggs on the market, and these may not be the most accessible for everyone. There's also differences between brown and white eggs that some people might consider before making their selection. The bottom line is that all eggs can be nutritious components of a balanced diet no matter which type you ultimately select.