Imposing on the Host
Answer: In a eulogy for his late wife delivered at Yeshivat Ohr Somayach where he teaches, the noted Torah scholar and historian Rabbi Berel Wein told of the time he invited a young man for a Shabbat meal. This fellow told his wife that he ate only peanut butter. Not missing a beat, this magnanimous hostess asked "Creamy or crunchy?"
Not everyone will respond with the generosity of a Rebbetzin Wein, but you can safely assume that if you inform your hosts in advance they will be glad to prepare your food without salt or with some safe substitute. But please don't wait till the last minute to pass on your request – and enjoy your meal.