Cum Grano Salis is a science fiction novella by Randal Garrett, first published in 1959, under the pen-name David Gordon.
“Just because a man can do something others can’t does not, unfortunately, mean he knows how to do it. One man could eat the native fruit and live ... but how?”
An exploratory expedition's food is destroyed in a freak accident, and the native fruits of the planet are mysteriously poisonous. Every Earth creature that eats them, dies; except MacNeil. He gets fat while everyone else starves.
Randall Garrett (1927-1987) was an American science fiction and fantasy author. He was a prolific contributor to Astounding and other science fiction magazines of the 1950s and 1960s. He instructed Robert Silverberg in the techniques of selling large quantities of action-adventure science fiction, and collaborated with him on two novels about Earth bringing civilization to an alien planet.