Risks and benefits of weight loss: challenges to obesity research

It is well accepted that being overweight or obese carries risks to health, but there is less agreement as to whether weight loss produces benefits on mortality and on cardiovascular event rates. The evidence from observational studies is conflicting: some studies have shown weight toss to be associated with increased mortality, but this could be because differentiation was not made between intentional and unintentional weight loss. Mechanistic hypotheses can be raised for both beneficial and harmful effects of weight toss. Randomized controlled clinical trials are needed to establish the effect of intentional weight loss and two large outcome studies are now under way: SCOUT and Look AHEAD. These trials are assessing the effect of weight loss on cardiovascular endpoints. Such trials are complex and expensive to undertake, but are important if we are to establish whether weight loss is truly associated with a reduction in mortality.