Do Overweight People Live Longer?

We've long known that too much excess weight increases your likelihood of dying prematurely. Or does it?

Obesity picture from Shutterstock

A large review of the evidence published in the Journal of the American Medical Association (JAMA) in January found that overweight people live longer than leaner people.

But don't reach for the pie and chips just yet.

There is no denying that the high and rising prevalence of obesity and overweight is a major health problem. With 70 per cent of men and 56 per cent of women either overweight or obese, Australia is among the worst-affected countries in the world.

We commonly measure body size with body mass index, or BMI: a person's weight in kilograms divided by the square of their height in metres. It is a good average measure of the amount of fat a person has in their body, which is useful for classifying people in population studies.

The World Health Organization (WHO) defines a "normal" BMI range as 18.5 to 24.9 and this corresponds to a weight of 49 to 65kg for Australian women of average height (1.62 m) and 58 to 77kg for men of average height (1.76 m).

Recent estimates have shown for the first time that a high BMI is now responsible for the greatest burden of disease in Australia and New Zealand, ahead of smoking and high blood pressure.

But the challenges represented by the obesity epidemic have raised the question of what the ideal BMI is for life expectancy.

Two large and well-conducted studies in the Lancet and New England Journal of Medicine examined this issue by gathering data on more than two million people who had their BMI calculated and were followed for their risk of dying over a defined time period.

The large numbers of participants and detailed individual data in these studies means the researchers were able to look at how small differences in BMI relate to the risk of death, accounting for a range of other factors known to influence this relationship, including illnesses that could potentially affect BMI.

Despite the diversity of populations covered by the studies, and the differences in methods, their findings are remarkably consistent: people with a BMI at the upper end of the WHO "normal" level (22.5 to 24.9) have the lowest death rates.

You can see this visually represented by the J-shaped curve in the graph below: as BMI goes up in increments of 2.5 above and below the 22.5-to-24.9 category, so do death rates.

Why do people with a BMI at the upper end of the "normal" range have the lowest risk of death?

People with BMIs above this optimal level have an increased risk of dying, especially from heart disease, most likely due to increases in blood pressure, cholesterol levels and diabetes caused by excess body fat. They also have an increased risk of dying of cancer.

People with BMI levels below the optimal level also have increased death rates, particularly from respiratory diseases (such as chronic bronchitis) and cancer. The increased risk of death in the people with lower BMIs may also be because chronic illness has caused them to lose weight.

So with this evidence in mind, how does the JAMA paper reach such a different conclusion?

It comes down to the way the data from each of the studies have been collated and presented.

The JAMA review used broad classifications for underweight, normal weight, overweight, and obese and very obese, rather than the 2.5 increments of BMI. People with a BMI of 18.5 to 24.9 were included in the "normal weight" category; we can see from the graph above that this broad category includes people with the lowest risk of death, combined with people with a higher risk of death.

The "normal weight" category was then used as the comparison group for the studies, and has an average risk of death that is higher than the risk in the broad "overweight" category.

This skews the optimal weight finding and changes the shape of the curve, from J-shaped to tick-shaped.

The result? One that suggests being overweight makes you live longer.

There are varying reasons why the researchers might have used these broad groups, including the fact that many studies are too small to be able to present statistically reliable results according to finer gradations in BMI.

The bottom line is that too much fat is bad for your health and increases your risk of dying prematurely. We still have a long way to go in our fight against obesity and, if anything, we need to redouble, not reduce, our efforts.

Emily Banks is Scientific Director of the 45 and Up Study at Sax Institute. She receives research funding from the National Health and Medical Research Council and the Australian Primary Health Care Research Institute. Rosemary Korda is a Research Fellow at the National Centre for Epidemiology and Population Health. She receives funding from NHMRC and ARC. Grace Joshy is a Research Fellow at the National Centre for Epidemiology and Population Health. She does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

The ConversationThis article was originally published at The Conversation. Read the original article.


Comments

    So the gist of this is, that people who are only very slightly overweight live longer!!
    People who are actually above that very small BMI factor will still die early if they don't lose weight! C'mon people, no one wants to carry your bloated fat corpse to the funeral... Put the fork down!! :)

      I consider myself to be in that "only slightly overweight" group, so hopefully I may still, 'just' make it to the singularity... :)

      Fork? I don't need a fork to eat pizza and chocolate.

    Except that the BMI is a ridiculously flawed way of identifying a person with a weight problem or a health problem. If you are extremely fit, for instance, and have more muscle mass than average, your BMI will be the same as someone carrying the same weight of excess fat. The one carrying the fat will be obese, the one carrying the muscle will be CLASSED as obese, but will actually be perfectly healthy.

    It's entirely possible that these results are skewed by healthy people with more muscle mass who are sitting in the "overweight" band of the BMI range.

      I'm not sure you read the article. When using finer-grained measurements, the best weight seems to be within the 'healthy' BMI range - it's just at the upper end of healthy. This includes people with a moderate amount of body fat or a moderate amount of muscle.

      The people you're referring to have enough muscle mass to be classed as overweight or obese by BMI. If they're healthy, they should be skewing the end of the graph - ie making the 'obese' category seem healthier than it really is. They don't really affect the conclusions of the study.

      BMI may be a bad measurement when applied to an individual, but it's not terrible when applied to whole populations. it's an easily-measured number that gives you an approximate idea of how everybody is doing as a whole.

    So technically you're saying you need to Put the fork down also? C'mon man, No one wants to carry your fat corpse to the funeral..

    I think it's even simpler than that - its not that overweight people live longer, it's just that we're defining overweight incorrectly. Height-to-weight ratio may be a good indicator to healthiness, but doesn't define the healthiness of a person.

    There's a lot more to this than weight, that science hasn't figured out yet. I've seen in three generations of one side of my family tree a twenty year difference between the least long lived and the most long lived people. No, it wasn't the size 8 women who lived longest. They died in their mid-60's. The size 24's lasted into their late 80's. This half of my family tree is Eastern European. The women who were size 8 have really had to fight for it. I don't think their bodies were meant to be a size 8 any more than a typical Brazilian woman is meant to be a size 20. Granted, a sample size of 7 isn't huge, but given that limited sample size, the observation above holds up.

    At first glance, I thought that was an overweight George Calombaris from Masterchef...

    Why is that guy putting the sauce on top of his burger? Who does that?

    The real question is: why do we consider the healthiest weight to be "overweight"? Someone screwed up the BMI scale.

    Couldn't this reflect that as people who were generally healthy and slim age they actually do slow down metabolically and hit the upper end of the normal weight range vs people
    Not eating sufficient or with Undiagnosed maladies getting thinner before dying?

    All three of the studies do seem to provide data implying that the "healthy" range for BMI should be pushed upwards a bit, making a BMI of ~25 the midpoint for the "Normal" range.

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