New report: Weight loss increases mortality

Overweight and obesity feature as number five on the WHO list of risk factors that lead to premature death. For many, the solution consists of going on one intensive slimming diet after the other, hoping that once the excessive weight has come off, they will be healthy again.

This is not the right way to go about it, according to a new report from Council on Health and Disease Prevention in Denmark in which prominent obesity researchers have reviewed the most important literature in the field to find out how weight loss affects the body.

The surprising conclusion is that weight loss does not lead to lower mortality. In fact, the report actually suggests the opposite, according to the head of the research group:

“Overweight people who lose weight have an average mortality rate that is about 15 percent higher than similar groups of overweight people who do not lose weight. One would expect that the former group would have a reduced risk of premature death, but in reality it is the other way round – the risk of dying increases if you lose weight,” says Professor Kim Overvad of the Department of Public Health – Institute of Epidemiology and Social Medicine, Aarhus University.

Report provides more questions than answers

The report was initiated by Overvad and his colleagues after having read about the latest research on the consequences of weight loss for overweight people.

“We have come across articles in the recent literature which show that when overweight people lose weight, they do not experience the benefits that we had expected to see,” says Overvad.

This prompted the researchers to review the literature in the field, and their conclusion turned out to be in line with their suspicion: healthy overweight people who lose weight do not experience health benefits; on the contrary, they have a greater risk of premature death than healthy overweight people who do not lose weight.

The new report aimed to find some answers to how best to advise and assist overweight people. In the end, however, the literature review actually resulted in more questions than answers.

“We have tried to find explanations in the literature to help us make recommendations for the overweight people. The studies that are currently available show unanimously that healthy overweight people who lose weight have a higher mortality; however, they provide no answers to why this is so,” says the professor.

How can weight loss be dangerous?

The research currently available on obesity does not provide an answer to the seemingly obvious question: ‘how on earth can weight loss be anything except good?’ Even after adjusting for other harmful factors such as increased consumption of tobacco or alcohol, which in themselves could lead to increased mortality, the literature provided no clear answers.

The authors of the new report have made some speculations about possible answers, but Overvad is keen to point out that they are “merely qualified guesses”.

The three possible explanations from the Danish researchers are:

1. Some of those who lose weight may actually be ‘incipient sick’, but at such an early stage that they have yet to discover any disease. If this is the case, they may have been feeling healthy but have still lost weight as a result of illness – and thus have a higher mortality.
2. Another possible explanation is that the overweight people have lost weight in an unhealthy manner, e.g. through extreme dieting, which usually only leads to temporary weight loss.
3. The third possible explanation is that the overweight people have lost the fat in the wrong places on the body. The literature does not specify what kind of fat the people have lost, so it is not possible to say whether it is the unhealthy belly fat or whether it is the fat that’s found in the buttocks and thighs, which may be healthy.

Conclusive answers are hard to come by

There have also been discussions about harmful substances that may be stored in the fatty tissue, which are released when we lose weight. Scientists know for instance that fatty tissue can store pesticides, but since this correlation has yet to be examined, it is not possible to say whether there is a correlation between high doses of pesticides in the body and a higher mortality in relation to weight loss.

On the whole, it is extremely difficult to fully grasp this issue, says Overvad. He does not think it is realistic to design experiments that would provide conclusive answers to these questions:

“The problem is that you need very large groups of overweight people. You need to change their weight using a specified diet modification or changes in physical activity, and then you need to monitor them for years afterwards. It is not realistic to imagine that this can be done in controlled ways for a sufficiently long time.”

There are many short-term studies of this kind, covering e.g. six months, but it is the longitudinal studies that are lacking. In order to say anything about mortality, studies with a duration of 15 years are required, he says.

Drop the slimming diet; focus on health instead

Despite the limitations of the new literature review, Overvad believes it reveals a need for a change of attitude when it comes to recommendations for overweight. We need to move away from thinking about the great slimming diet in January or just before the bikini season and redirect our focus to what actually constitutes a healthy life.

“Our main message is that we should move our focus away from using the bathroom scale as an indicator and start looking at the healthy life as an indicator.”

The suggestion that we should drop the slimming diets does not entail that we should focus less on a healthy diet and lots of exercise. On the contrary. The new research results set the stage for an even stronger focus on a healthy lifestyle, says Overvad. If there are no guaranteed health benefits associated with losing weight, while great health risks are associated with being overweight, our main efforts should go into avoiding weight gain in the first place, he argues.

The new report is currently available in Danish only has an English abstract – see link below this article.

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Read the Danish version of this article at videnskab.dk

Translated by: Dann Vinther

Scientific links

• The Danish report: 'Skal overvægtige voksne tabe sig?' ('Should overweight adults lose weight?' Vidensråd for Forebyggelse (2013)

External links

• Kim Overvad’s profile (Aarhus University)

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