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I tried Googling but got no significant trustworthy result in the top few searches. The only reference I found is here: where the answered has guaranteed it without any reference!

Yes Egg shell is made from calcium and the hydrochloric acid that the stomach produces will rapidly dissolve it.

Can anyone provide me a solid answer backed up by solid references? I also heard from one of my friends that stomach can not digest egg shell efficiently. So when peeling an Egg shell we must be careful because as it can remain undigested, it can stick in out penis and create problem in urinating. Although it sounded ridiculous to me (isn't it?) , I am more interested in finding whether stomach can digest it or not.

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    Considering egg shells dissolve in vinegar (fun home science experiment) I can't imagine they won't be digested.
    – Sam I Am
    Commented Jan 2, 2013 at 5:59
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    I didn't downvote, but there appears to be no notable claim here. As far as the vinegar question, acetic acid (vinegar) has a pH of around 3 whereas gastric acid has a pH of around 2, so it is more acidic. Its however, just speculation on my part, but the shell-less egg experiment is still very cool.
    – Sam I Am
    Commented Jan 2, 2013 at 6:16
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    The quote is essentially correct, except that egg shells are made of calcium carbonate. This is a nontrivial distinction as elemental calcium is a very soft, highly reactive metal. Your friend need have no fear of getting eggshell caught in his/her urethra as the bladder isn't even connected to the digestive tract but rather to the kidneys, which filter blood plasma.
    – Richard Terrett
    Commented Jan 2, 2013 at 10:06
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    I wonder if the original claim was "Egg shells are high in calcium, which increases the risk of calcium oxalate forming kidney stones, which cause problems urinating." A brief look online suggests a diet LOW in calcium is associated with kidney stones which is surprising, and would make this claim false.
    – Oddthinking ♦
    Commented Jan 2, 2013 at 12:23
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    As a comment, just because the pH of stomach acid could dissolve egg shells doesn't mean that they will dissolve. There are a lot of other factors involved such as surface area, residence time, being surrounded by other food items, etc... Once the shells leave the stomach there would be no more digestion. Anecdotally, on the several occasions when my dog has eaten eggs shells, much of the shell passed though the digestive system without being broken down.
    – DQdlM
    Commented Jan 2, 2013 at 15:19

1 Answer 1

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There have been studies that attempt to show egg shells can be a viable source of calcium. The egg shells are ingested in a powdered form, and prove a viable source of calcium for human consumption.

Sources

Chicken eggshell powder (ESP) might be an attractive source of Ca for human nutrition. To study its nutritional value, we analyzed minerals, amino acids, and hormones in commercially available Slovakian ESP.
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Therefore, ESP seems to have a beneficial composition with about 39% of elemental Ca, relevant amounts of Sr, and low levels of Al, Pb, Cd and Hg. It may be used as a Ca source in human nutrition.

—Mineral, amino acid, and hormonal composition of chicken eggshell powder and the evaluation of its use in human nutrition.

The present study indicates that healthy late post-menopausal women with an adequate Ca intake at baseline may increase BMD of the hip within 12 months following supplementation with the chicken eggshell powder-enriched supplement.

—Positive effects of a chicken eggshell powder-enriched vitamin–mineral supplement on femoral neck bone mineral density in healthy late post-menopausal Dutch women.

Powdered chicken eggshells might be an interesting and widely available source of calcium. In two studies using piglets we determined the digestibility of calcium from different diets.
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Our conclusion is that eggshell powder is, in the case of casein-based diets, as good a source of calcium as CaCO3 and, in the case of soya protein-based diets, better than CaCO3 for growing piglets. As the piglet model is considered to be representative for humans, chicken eggshell powder is also a promising source of calcium for human nutrition.

—Eggshell powder, a comparable or better source of calcium than purified calcium carbonate: piglet studies.

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    I can't remember the name of the book, unfortunately, but it was about a family that worked at a Christian school in China during WWII, that got turned into a concentration camp by the Japanese. In there, they mention using eggshells as calcium supplements.
    – Clockwork-Muse
    Commented Jan 2, 2013 at 19:26

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