This formula's own materials cite three specific, real external sources — worth checking each one directly rather than assuming what they cover.
An NIH dietary-supplement fact-sheet index, a PubMed search page for apple cider vinegar and weight, and a separate PubMed search page for berberine and metabolic health.
Linking to an actual government institution and an indexed research database, rather than vague "studies show" language, is worth crediting as a transparency signal — while still reading each source as general category research, not a trial of this specific finished formula.