Salty foods contain sodium, which is the main chemical that we are concerned with here. Sodium is an important substance in the body which regulates how the body holds on to water. The more sodium you ingest, the more water your body retains.
The major effect of sodium ingestion, as you have pointed out, is that it will cause an increase in blood pressure. For this reason, those who have high blood pressure
need to watch the amount of salt that they eat. There are a few other conditions where salt ingestion is a problem as well, such as other heart conditions.
You do make a good point that salt ingestion is probably not as big of a problem if you have normal blood pressure. However, there are studies which show that those who ingest a lot of salt are at higher risk of developing high blood pressure and other problems down the road. Therefore, reducing your salt consumption can be viewed as a generally positive healthy lifestyle move. Furthermore, it is important to have regular health checkups with your primary care doctor
, to make sure that your blood pressure remains well controlled. A good opportunity would be your annual physical