Putting fat from healthy mice into mice that can't make a certain protein helps the sick mice process sugar better and improves their hormone levels related to metabolism.

What we've found so far suggests that transplanting fat from normal mice into mice that lack the ability to produce FGF21 may improve how well those mice process sugar and regulate metabolic hormones [1]. Our analysis of the available evidence shows this effect is supported by 43.0 assertions, with no studies or claims found that refute it [1]. We looked at what happens when fat tissue is moved from healthy mice into mice that can’t make a certain protein—FGF21—which plays a role in metabolism. The evidence we’ve reviewed indicates that this fat transfer appears to help the recipient mice handle sugar more effectively and improves hormone signals tied to metabolic health [1]. This suggests that factors present in the transplanted fat may influence insulin sensitivity, even in animals missing FGF21. Right now, the data we’ve analyzed leans toward a beneficial effect. However, we base this only on the assertions we’ve reviewed so far. We don’t know the exact number of studies behind these assertions, nor do we have details on the methods, sample sizes, or long-term outcomes. Because of this, we can’t say how strong or consistent the effect is across different conditions. Our current analysis doesn’t allow us to determine whether the improvement is large, small, or how long it lasts. We also don’t know what specific components in the transplanted fat are responsible. As always, we’re updating our understanding as more evidence becomes available. Practical takeaway: In lab mice, moving fat from healthy animals into those that can’t make FGF21 seems to help their bodies process sugar better—but we don’t yet know how this could relate to treatments or human health.