The increase in life expectancy is one of the great success stories. If you were born in 1870, you would expect to live to be 30 years old. But if he was born today, I would expect suppose live to 72 years, and the UN predicts that it will continue to rise to 82 years by the year 2100. Australian life expectancy is currently 84.
There’s the occasional flicker: world wars, famines, pandemics (even COVID seems to have knocked a year or so off life expectancy globally) – but over time, it keeps marching on.
That’s why I was surprised to read a Queensland Health and Wellness report, a government agency, which suggests that life expectancy will drop by between 0.6 and 4.1 years for children born in Queensland next year. According to the report, the problem is obesity.
While being overweight and obese increases the risk of serious illness, it does not mean that children born in Queensland or the rest of Australia will have a shorter life expectancy.
Childhood obesity isn’t increasing much, but we do gain weight as we age
The proportion of overweight and obese children in Australia has increased very rapidly since around 1970, but stabilized at about 25% in the mid-1990s, and has remained there practically ever since.
But the probability of being overweight or obese increases throughout life, or at least into old age. So as the current crop of kids get older, they get heavier. By the time I was 40 years old, 55% of my cohort was overweight or obese. When I was 60 years old, it was 75%.
Life expectancy and obesity have increased
Obesity increases the risk of the major killer diseases: heart disease, stroke, diabetes and cancer, and many other conditions.
Therefore, argues the Queensland Health and Wellness report, we can expect a tsunami of obesity-related deaths in the future, even without an increase in current levels of childhood obesity.
At first glance, this sounds plausible.
But life expectancy has been rising in countries where obesity has been on the rise for decades. Obesity-related reduction in life expectancy previously foretold it has not happened
Read more:
The paradoxical impact of obesity on life expectancy trends
Obesity is associated with an increased risk of death, but being moderately overweight is not
A series of studies implying millions of people have found, rather counterintuitively, that although people who are slightly overweight are more likely to suffer from heart disease and diabetes, or suffer from stroke, they live longer.
These studies find that life expectancy is longer with a body mass index (BMI) of around 27: roughly in the middle of the overweight range.
However, obesity (BMI of 30 or more) is consistently associated with an increased risk of premature death.
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So what is the problem with the report?
First, the report assumes that “business as usual,” that is, childhood obesity levels will remain high and the risk of disease and death associated with a given level of fatness will not change.
But business is never business as usual. Medical treatments improve, diet and activity change.
In fact, several studies have found that the level of fatness associated with the lowest risk of death has been increasing over time.
A study in danish found that in a 1977 cohort, the lowest risk of death occurred at a BMI of 24. By 1992, it was 25, and by 2008 it was 27. This likely reflects better medical management of overweight or obese people.
So when these children reach adulthood, even if they remain obese, their chance of dying prematurely will be less than it is today.
Read more:
Obesity has become the new normal, but it is still a health risk
Some data supporting the model is questionable
There is a second problem with this report. To calculate how much being overweight or obese increases the risk of death, the report is based on a 2009 study by a group based at Oxford University called The Prospective Studies Collaboration.
In contrast to the studies mentioned above, this study found that the risk of death was lower at a BMI of approximately 23-24.
However, the study was based in part on self-reported height and weight, and people tend to underestimate their BMI (we all think we’re a little taller and a little thinner than we really are).
This bias means that in these self-report-based studies, the lower risk of death actually occurs at higher BMI, rather than the reported 23-24.
This methodological flaw (and others) have been he pointed in relation to a different study using a similar methodology.
Another problem is that as we age, the BMI associated with the lowest risk of death increases. a british study found that before age 50, the “less lethal” BMI is about 23. At age 80, it’s closer to 28.
So as people age, higher levels of fat carry fewer risks. This may be because fat provides a nutritional reserve, cushions falls, or because older people receive better medical care.
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Separating science from activism
Finally, I am concerned that the report is overtly activist in intent.
The executive summary states that “to build social license” for changes such as sugar taxes and advertising bans:
people need to accept the seriousness of the situation and believe that maintaining a healthy weight for children is not just a parental responsibility.
This conclusion is nowhere justified by this report. The report does not look at the factors that drive obesity at all. It simply makes a mathematical projection of life expectancy.
Predictions about life expectancy arise from time to time, and we must always be careful to take them at face value. Like the American baseball player Yogi Berra said“It’s hard to make predictions, especially about the future.”
Read more:
Australia is dragging its feet on healthy eating. In 5 years we have made unfortunate progress
