Your surety is misplaced and unfortunately you're not even asking the right question. The relationship between salt and blood pressure is a complex, multi-factorial issue which can't be adequately summarized in a comment here. The best explanation I've heard is this interview with Rick Johnson, MD who is one of the most prominent researchers in that field. It's long but worth a listen.

https://peterattiamd.com/rickjohnson/

I don't really care how complex it is. Split people between two groups, offer food with half the salt to one group and see what happens. No need to overcomplicate.