Foods that have salt and ones that are made from grains or pulses are not supposed to be consumed during fasting. What is the reason for such a practice?
Fasting is a way of stomach + mind purification. In a philosophical way it's also "Tyaag"; i.e. giving away (certain) desires. Ideally during fasting, foods itself are not allowed. But in modern times, we have taken some liberties. At least those consumable foods are prescribed to be of "Saatvik" nature.
Salty/Spicy food are of "Rajasic" nature which stimulates desires, and kills the very purpose of fasting!
Lord Krishna from Bhagavad Gita, Chapter 17.9:
Foods that are too bitter, too sour, salty, hot, pungent, dry and burning are dear to those in the mode of passion. Such foods cause distress, misery and disease.