Should you ever be stranded on an alien planet, be careful what you eat! Even if none of the native edibles contain deadly poisons, you may develop serious nutritive deficiencies regardless of how much you eat. You see, the protein in these organisms (if there even is any) could be made up of D-amino acids, and/or amino acids that are not incorporated into terrestrial metabolism*. Relying on these organisms as a food source could result in (eventually fatal) amino acid deficiency, which you might not recognize until it's too late.

* Chirality (somewhat simplified) is a property of molecules that are asymmetrical. A particular molecule can exist in a "right-handed" (D) form or "left-handed" (L) form. Ordinary chemical reactions create the two forms ("stereoisomers") in roughly equal amounts.

Essentially all amino acids found in terrestrial life forms are of the L-type. All amino acids found in proteins are L-type.This is because enzymatic reactions that occur in cells only produce this type.

In addition, all proteins are made up of only 20 different amino acids, with only a few modified forms present in some cases.

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