Weight loss and mortality in persons with type-2 diabetes mellitus: a review of the epidemiological evidence.

Six epidemiological studies of weight loss and mortality in persons with diabetes are reviewed in this paper. One study found no relationship between weight loss and mortality, one study (published as an abstract) found that weight loss was associated with reduced mortality, and in two studies the results were mixed: in some groups weight loss was associated with increased mortality and in other subgroups weight loss was associated with reduced mortality. The most appropriate interpretation from this group of studies is that the relationship between weight loss and mortality in persons with diabetes is equivocal. None of these studies were designed to experimentally test the hypothesis that intentional weight loss increases survival in persons with diabetes. Because weight loss was not randomly assigned to the study participants, and because the reasons that the participants lost weight are not made clear, we can only conjecture about the potential confounding role that underlying illness plays in accounting for these results. In addition, the epidemiological evidence suggests that persons with diabetes are more likely than non-diabetics to experience both intentional and unintentional weight loss. This fact makes it especially difficult to cleanly separate the potentially opposing effects of intentional and unintentional weight loss in observational studies. Because of the important limitations and inconsistencies in the results of the studies reviewed here, the clinical community is left with little guidance on the relative role that intentional weight loss should play in the care of persons with diabetes, compared with better established treatments. Although better designed observational epidemiological studies are needed, the best test of the hypothesis that weight loss improves survival in persons with diabetes will come from randomised controlled trials.