The nature of the "health-food fanatic" argument is that naturally
occurring chemicals are available in a context in which they are
mixed with some number of adulterants that may have nutritional or
buffering effects that we may or may not know about.

In some cases this can be refuted; in fact, in the case of sea salt,
there are some adulterants that are likely to be detrimental, such
as heavy metals (though they may occur only in insignificant
quantities). In other cases, we may simply not know whether the
naturally occurring substances contain some trace component that
is nutritionally significant. A "health food fanatic" may really
be fanatic, or may be arguing, more moderately, that we should
eat the naturally occurring version just in case there is something
important in it that we don't know about. Sometimes the processes
we use to make food-production more convenient or economical have
undesirable side-effects, such as introducing adulterants whose
effects we do not know, or whose effects are known to be harmful.
As an example, antibiotic-treated cattle are reported to bear bacteria
that have developed resistance to antibiotics. If any
of these bacteria happen to be human-disease agents, treating an infection
caused by them may be complicated by this resistance.