When a year or location in parens follows a journal title it is there because more than one journal has that name. As @adamsmith says, the parenthetical suffix is _necessary_ to accurately point the citation to a single specific journal. There are two current journals with the name "Clinical Nutrition"; a third current journal that is a non-English publication that prominently uses that English title (it was the first to use that name); and two other inactive journals with that title. Indeed, "your" Clinical Nutrition wasn't the first English journal to be published with that title.

The existence of multiple journals with the same title, while not quite common, isn't rare. Without the disambiguation it would not be clear which of the journals contains the citation.