EU referendum, brexit and the aftermath

Half true. It's called chirality and is exploited as a property for artificial sweeteners. Proteins, sugars, enzymes, etc. all have a handedness and only work with molecules of the same handedness.

There's an easy way to understand chirality. Hold out your hands, palms facing each other. Imagine that each hand is the chemical structure of a molecule. Most complex molecules are chiral. Like your hands, the two structures of chiral molecules - in sugars, they're referred to as D and L, from the Latin dexter and laevus - differ only in the arrangement of their elements. Put your hands together and they seem to match exactly. In the same way, the common sugar D-glucose is the mirror image of L-glucose, its rare counterpart. But put your hands down one on top of the other, both facing down, and you'll see that they're not identical at all; they're what chemists call non-superimposable.

Two enantiomers of a molecule will respond identically in a chemical reaction, but not so in biological systems. Proteins and cell receptors are designed to react only with particular enantiomers. For example, the enzymes in your stomach can digest only right-handed sugars. Just as a glove fits only on the proper hand, our bodies distinguish between the enantiomers of any given molecule.

https://www.wired.com/2003/11/newsugar/

Say a left-handed human (in terms of chemistry, not hands) shows up on a right-handed planet - they'd probably die after a couple of weeks despite eating normally because they would be unable to digest any protein, fat, complex sugars, etc.