Take with a grain of salt and take with a pinch of salt are two idioms which mean the same thing. We will look at the definition of the phrases take with a grain of salt and take with a pinch of salt, their origins, and some examples of their use in sentences.
To take with a grain of salt and to take with a pinch of salt mean to accept the truthfulness of a statement or the accuracy of a statement with skepticism. The assumption here is that as food is more palatable when seasoned with salt and therefore easier to swallow, a less than truthful or accurate statement is easier to swallow if a grain of salt is added. Though the admonition to take an antidote with a grain of salt is found in the writings of Pliny the Elder in the 70s, the use of this term as an idiom didn’t occur until the mid-1600s. The term to take with a pinch of salt first occurs even more recently, in the mid-1900s. Related terms are takes with a grain or pinch of salt, taken with a grain or pinch of salt, took with a grain or pinch of salt, taking with a grain or pinch of salt.
I am not sure where you stand on polls, but I believe there are four basic categories that polls fall into: love, hate, take with a grain of salt or believe as gospel. (The San Luis Obispo Tribune)
We may take with a pinch of salt the idea of a sermon on a mountain top, but there are reliable reports of people addressing quite large crowds long before microphones were invented. (The Hong Kong Free Press)