Australasian Science: Australia's authority on science since 1938

When Can Weight Loss Be Dangerous?

By Tim Olds

Unless they are extremely obese to start with, people who lose weight die younger.

If you’re overweight or obese – and that’s about 60% of us – then losing weight will improve your blood pressure, blood fats, blood glucose levels and insulin sensitivity. Weight gain has the opposite effects.

You would think, then, that overweight or obese people who lose weight would live longer, given that cardiovascular disease and diabetes are two of the major killers in Australia. This logic has driven a number of public health campaigns that urge anyone who is overweight or obese to lose weight. You may have seen the Measure Up campaign – the poor bloke huffing and puffing his way along the tape measure getting fatter and fatter, unable to keep up with his young daughter.

While that seems to make sense, it isn’t true. I’ve indicated before in this column that overweight people live longer, but now there is even more perplexing news: unless they are extremely obese to start with, people who lose weight die younger.

First, let’s look at some of the studies. Danish epidemiologist Thorkild Sørensen followed 2957 Finns from 1975 to 1999.1 They were aged 24–60 at the start. In 1975 he asked them whether they intended to lose weight – about one-third said they did. Relative to those who did not intend to lose weight, and whose weight remained stable 6 years later, those intending to lose weight who did actually lose weight had an 87% greater chance of dying. The authors’ conclusion: “Deliberate weight loss in overweight individuals without known co-morbidities may be hazardous in the long term”.

A US study2 followed 9538 Americans aged 51–77 in 1992 for 16 years, and calculated death rates according to initial weight status and change in weight. Those most likely to die were superobese individuals who gained weight – no surprises there – but normal weight people who lost weight had a 64% increased chance of dying. The groups with the best survival rates were overweight people who maintained their weight, followed by overweight people who became obese. The authors concluded that “in people who are overweight at 51 years of age, small weight gains do not lower the probability of survival,” whereas even a small weight loss (about 3 kg) in a normal weight person can significantly decrease survival.

Another American study followed 13,104 people aged 50–70 years in 1992 for 14 years.3 In people who lost a lot of weight (about 10–15 kg), those who were initially normal weight to overweight were 127% more likely to die, and those who were overweight to obese were 61% more likely to die. Even a small weight loss (3–5 kg) increased the risk of death in normal to moderately obese people by 15–20%. However, those who gained 3–5 kg were about 10–15% less likely to die – although the differences were not statistically significant.

In all of these studies, losing weight for very obese people (above 115 kg for a man of average height, or 100 kg for a woman) either reduced the risk of death or tended to. But for just about everybody else, losing weight increased the risk of death or had no effect, and gaining weight had no effect.

So what could be behind these perplexing results? One explanation is that those who lose weight do so because they have some underlying condition that also leads to an early death. But these results are unchanged when adjustments are made for baseline health status and health habits, and, in Sørensen’s study, for intention to lose weight.

Some have suggested that a little bit of padding may help us – it is a nutritional reserve, and may protect against damage when elderly people fall. Or it may be that people who are getting fatter get better attention from doctors.

Whatever the reason, the evidence is not currently supporting blanket public health recommendations that everyone who is overweight or obese should lose weight.

And there’s a little twist in Sørensen’s study about intentional and unintentional weight loss that should make us stop and think a bit about weight loss. Of those intending to lose weight, 38% had actually lost weight at a 6-year follow up. That sounds pretty good, until we learn that the percentage of people losing weight among those who did not intend to lose weight was … 38%!



Professor Tim Olds leads the Health and Use of Time Group at the Sansom Institute for Health Research, University of South Australia.