"Chicken eggs are made up of mostly water, protein, and fat. Plus, a small number of minerals like calcium carbonate that make up the shell.
All of these things can be found in a chicken's diet, and as long as she's getting enough to eat and the right amount of sunlight, she'll lay eggs whether they're fertilized or not."
https://chickenandchicksinfo.com/why-do-chickens-lay-unfertilized-eggs/