Insulin might help the kidneys get rid of more water in rats—even when the body’s usual water-control system isn’t working—because it directly affects the kidneys.

What we've found so far is that insulin may increase urine output in rats, even when the antidiuretic system—the body’s main system for controlling water balance—is blocked [1]. Our analysis of the available research suggests this effect could happen because insulin acts directly on the kidneys, not through the usual hormonal pathways [1]. The evidence we've reviewed leans toward the idea that insulin influences how much water the kidneys release, regardless of whether the antidiuretic system is working [1]. In studies done on rats, insulin appeared to boost the amount of water lost in urine, suggesting it has a direct role in kidney function [1]. This is notable because it points to a pathway that might work independently of the body’s standard water-regulation system. Right now, we only have a limited number of studies to draw from—just one assertion based on 10.0 supporting studies and no studies that refute it [1]. While the direction of the evidence is consistent, we don’t yet know how strong or reliable this effect is across different conditions or over time. Our current analysis can’t rule out the possibility that other unmeasured factors could be involved. Because this is based on animal studies and only one line of evidence so far, we can’t say how this might relate to humans or real-world health outcomes. Still, it adds to our understanding of how insulin might affect the body beyond its role in blood sugar control. Practical takeaway: In lab rats, insulin seems to help the kidneys release more water, even when the body’s usual system for managing water is turned off. But we need more data to understand how this works and whether it matters for long-term health.