Im struggling on this how does the 4th principle part match a sentence in latin

The fourth principal part, as the perfect passive participle, is an adjective.  Usually just the masculine nominative singular is given.  The complete forms are: -us, -a, -um.

N.B.: intransitive verbs do not have a regular 4th principal part (because they can’t be made passive); this includes the verbs that take a dative (noceō, pāreō, etc.)

  Some are listed as –tum/-sum, which is the supine.

 Some have forms in -tūrus/-sūrus (e.g. sum – futūrus; veniō – ventūrus; fugiō – fugitūrus), which is the future active participle

Some have no fourth form: (e.g. timeō – –; noceō —)

There are a few different uses for the fourth principle part. It is used to form passive verbs (both indicative and subjunctive)

Explanation:

lab rats that ate more artifical sweeter gained more weight than those who ate sugar and they had “lower levels of a hormone called glp-1, which affects how full we feel.”