Losing weight and keeping it off is so hard for the vasty majority of dieters. It's hard to find any study in which the majority of participants lose a lot of weight long-term. For some studies, the bar for dieting 'success' is as low as losing a few percent of starting weight and keeping it off for a couple years, which is almost indistinguishable from water fluctuations. There are outliers, but more research needs to be done as to why they are successful.
