The health effects of weight loss need more research

Although it seems obvious that when overweight people lose weight their health should improve, the relationship between weight loss and health may not be as simple as that, suggests previous studies from Finland and Denmark. For example, it is difficult to control for all other possible things that might cause weight loss, such as other medical conditions that could then increase mortality.

The researchers at the University of Helsinki, Helsinki and Copenhagen University Hospitals, Danish Epidemiology Science Center and National Public Health Institute in Finland started with a population of 19 993 Finnish twins who were asked in 1975 about their weight and whether they were attempting to lose weight. In 1981, they were asked again about their weight, and then followed for up to 18 years to see who died. The researchers looked at the 2 957 who were overweight or obese (BMI at least 25) and took out of the analyses all the people who had illnesses, or those who had data missing, and analysed mortality against intention to lose weight in 1975 and actual change in weight.

They found that those people who intended to lose weight and who actually did so had a somewhat higher mortality than those who gained weight or whose weight remained the same. In people who did not intend to lose weight, gaining weight was associated with a somewhat higher mortality.

What do these results mean? In the people studied here who were otherwise healthy losing weight seemed to be associated with higher mortality. What makes these results quite difficult to interpret is that it is not clear what caused the increased risk, but nonetheless intentional weight loss did not improve mortality.

The findings need to be replicated in other studies and need to be better understood before they can be used for recommendations to people.

In people who have medical conditions related to obesity, losing weight is obviously desirable, emphasize the researchers. But overall, preventing people, especially children, from becoming overweight in the first place seems crucial, since this work suggests that once weight is gained losing it again may not be good for health.