Cranberry fiber, derived from the fruit of the cranberry (Vaccinium macrocarpon), is used to support the bladder and urinary tract primarily due to its content of bioactive compounds, especially proanthocyanidins (PACs). Scientific studies have shown that cranberry products, including juice and extracts, can help reduce the recurrence of urinary tract infections (UTIs), particularly in women, by preventing the adhesion of certain bacteria (notably Escherichia coli) to the urinary tract lining. Most clinical research focuses on cranberry juice or extract, but cranberry fiber may also contain some of these active compounds along with prebiotic fibers that could support urinary and gut health.

The evidence for cranberry fiber specifically is less robust than for juice or extract, but it is reasonable to infer some benefit since the fiber may retain relevant phytochemicals. A 2016 Cochrane review found a modest reduction in UTI recurrence with cranberry products overall, though results were mixed and effectiveness can depend on the form and dose used. There is limited direct clinical research on cranberry fiber alone for bladder health, so the rating reflects moderate evidence for cranberry products in general, with some uncertainty about the efficacy of the fiber form in particular.

In summary, scientific evidence suggests cranberry components can support bladder health, mainly by reducing bacterial adhesion and thus UTI risk, but more targeted research on cranberry fiber itself is warranted.