They're actually a great source of calcium!
Besides throwing them away, there are a few ways you can use eggshells. They're great as fertilizer for your garden, perfect for compost—and you can eat them. Yes, you read that right. Eggshells are edible, and there's some pretty compelling evidence that eating eggshells can be good for your health, especially if you're looking to increase your calcium intake. According to experts at the University of Florida's Institute of Food and Agricultural Sciences, a single eggshell contains about 2.2 grams of calcium. The average adult, between the ages of 19 and 50, should consume about 1 gram of calcium daily, according to the US National Institutes of Health. So if you're an adult who eats their fried egg with a side of eggshell, you'll be getting almost twice your daily recommended dose of calcium.
This evidence that eggshells are good for your health is backed up by some clinical and scientific studies. A 2003 review published in The International Journal of Clinical Pharmacology Research found that eggshell powder—which is basically just crushed eggshells—is a good source of calcium and "may have a positive effect on bone metabolism." This was particularly significant for older women with osteoporosis; the researchers noted that in clinical studies of postmenopausal women and women with the disease that causes bones to weaken, eggshell powder reduced pain and increased mobility and bone density, or, at the very least, "arrests its loss."
Crushing up eggshells into a powder is probably the most pleasant way to eat eggshells. A more recent study, from a 2013 issue of the International Journal of Food Sciences and Nutrition, notes that though adding powdered eggshells to spaghetti, bread, or pizza slightly changed the texture, there were not notable changes in flavor—and that seems like a fair trade-off if you're looking to up your daily calcium intake.
If you're sold on the idea of turning your eggshells into eggshell powder for extra calcium, please do remember to cook them first. That way, you kill any bacteria that might be lurking on your raw eggshells, waiting to make you sick. There are a few YouTube tutorials on how to make eggshell powder safely, including this one from TechInsider, which calls for boiling and then baking your eggshells at 200°F before crushing up in a blender:
Or you could go the route of YouTuber L.A. Beast and just eat the raw egg whole:
Don't actually do that, though, because that cracking sound is enough to make my toes curl. (You also run the risk of getting sick with salmonella, which would be bad.)
But the next time you see a broken eggshell in your omelet, don't freak out about trying to fish it out for fear of cracking your teeth or whatever. After all, it's just extra calcium.