In short
Fisetin is a flavonoid found in strawberries and several other fruits and vegetables that has been identified in laboratory screens as having senolytic activity — the ability to selectively induce death in senescent cells.
In a 2018 screening study by the Mayo Clinic/Scripps research group (Zhu et al., EBioMedicine) testing a panel of flavonoids for senolytic activity in cultured cells, fisetin emerged as one of the more potent candidates tested, and the same paper reported that fisetin extended median and maximum lifespan in mice when given later in life, alongside reducing several senescence markers in aged mouse tissue.
Unlike D+Q, fisetin is a single compound rather than a combination, and has since progressed into early human clinical trials — including a National Institute on Aging-funded trial in older adults and trials in specific conditions like chronic kidney disease — that are testing safety, senescence-marker changes, and functional outcomes. As of this writing, published human results are limited to safety and small pilot-scale findings rather than large, completed efficacy trials.
Fisetin's mouse lifespan-extension data is genuinely more robust within the senolytic category than most alternatives, but this remains animal-model evidence; no completed human trial has demonstrated that fisetin extends human lifespan or reliably clears senescent cells at the doses used in commercially available supplements, which are typically far higher than typical dietary intake from fruit and have not been validated at that dose in humans the way the mouse studies validated their dosing in mice.