Sunday, 25 August 2013

Health myths: Being a bit overweight shortens life

reposted from:
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Health myths: Being a bit overweight shortens life
26 August 2013 by Caroline Williams

Let's be clear – being seriously obese is bad for your health. A body mass index of over 40 increases the risk of type 2 diabetes, heart disease and certain cancers and increases the risk of dying from any cause by up to 29 per cent. This is not a health myth.

But carrying just a few extra pounds, far from being a one-way ticket to an early grave, seems to deter the grim reaper, according to a recent review of nearly a hundred studies involving nearly 3 million people. The review, led by Katherine Flegal of the US Centers for Disease Control in Hyattsville, Maryland, reported earlier this year that being "overweight" – defined as having a body mass index (BMI) of 25 to 29 – seems to have a protective effect, with a 6 per cent ...

Random-effects summary all-cause mortality Hazard Ratios (HRs) for overweight (BMI of 25-<30), obesity (BMI of ≥30), grade 1 obesity (BMI of 30-<35), and grades 2 and 3 obesity (BMI of ≥35) were calculated relative to normal weight (BMI of 18.5-<25). The summary HRs were 0.94 (95% CI, 0.91-0.96) for overweight, 1.18 (95% CI, 1.12-1.25) for obesity (all grades combined), 0.95 (95% CI, 0.88-1.01) for grade 1 obesity, and 1.29 (95% CI, 1.18-1.41) for grades 2 and 3 obesity. These findings persisted when limited to studies with measured weight and height that were considered to be adequately adjusted. The HRs tended to be higher when weight and height were self-reported rather than measured.

Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality. The use of predefined standard BMI groupings can facilitate between-study comparisons.

Full details:

Comment: - lists strengths and weakness.

"... Our study also has limitations. It addresses only all-cause mortality and not morbidity or cause-specific mortality. It addresses only findings related to BMI and not to other aspects of body composition such as visceral fat or fat distribution..."

NHS Direct review

"However, a slight increase in lifespan doesn’t necessarily equate to an increased quality of life. Even being ‘just’ overweight can increase the chance of developing long-term health conditions, which while may not be fatal, can make life a lot less enjoyable."


"The headlines also did not make clear that the increase in life expectancy in people who were overweight or ‘mildly’ obese was modest – they were only 6% less likely to have died by the end of the study period than those of a healthy weight."


This systematic review included a meta-analysis of 97 studies comprising data on 2.88 million people and 270,000 deaths.


This systematic review provides high-quality evidence that obesity grades 2 and 3 are associated with higher death rates from any cause compared to normal weight individuals (around 30% increased risk). However, it also shows that lower grades of obesity (grade 1) do not increase the risk of death relative to normal-weight individuals and, in fact, overweight people had a small but significant reduction in their risk of death in the region of 6%.

The strengths of this review include the large number of studies it included and its standardised approach to searching and extracting data from the literature. Hence, we can be reasonably confident these results reflect reality.

However, a limitation of the study is that it only assessed the risk of dying from any cause (‘all-cause’ mortality), rather than death from specific diseases such as cancer, heart disease or diabetes. The association between weight and risk of death for different disease categories may vary. Disability and living with long-term diseases are also important to people and some conditions such as diabetes may show stronger links with weight at lower thresholds of BMI.

The review also crucially chose BMI as the measure of weight, which has been mistakenly taken by the media to mean an accurate measure of unhealthy ‘fatness’. BMI is a pragmatic choice to assess weight but it does not account for other known disease and death risk factors such as differing fat levels, fat distribution, muscularity, nutritional balance and others. BMI is also an imperfect measure of fatness as it only measures weight and height. Hence, those who are overweight are not all necessarily overweight because they are carrying excess fat. For instance, someone who is very muscular can have a high BMI and therefore be categorised as overweight.

Other measures such as waist circumference offer alternative ways of quickly estimating a person’s body fat levels and whether they are of a healthy weight. In practice, BMI is not the only measure used when establishing risk of disease or death. Doctors will be checking for a host of risk factors like high blood pressure, high cholesterol and high blood glucose levels in addition to BMI and/or waist circumference. Hence, the BMI category is only one of many measures used by a doctor to assess health, and by no means the best.

The finding that overweight individuals were at slightly less risk of dying than their normal-weight counterparts had been reported in research before (this is often referred to as the obesity paradox).

Possible explanations why a bit of extra weight may extend life include:

  • People with more fat reserves to rely on may survive better if they lose weight due to ill health as they get older.
  • Problems associated with being overweight (high blood pressure and diabetes) are picked up and treated earlier in overweight people compared with normal weight, as doctors are more vigilant of risk factors in overweight people. This treatment improves their health overall.

However, it is important to note that these are largely unsubstantiated theories and have not been further explored or proven.

The bottom line is that being obese (all categories combined) increased the chance of dying compared to those with a normal BMI. This was not the case for overweight individuals or the lowest category of obesity (grade 1) on its own.

It is important to consider that individual risk factors for developing disease and death will vary person to person and BMI is only one of many measures used to assess the risk of developing disease in the future.

Even if you choose to ignore the limitations of this research, it would be unwise to interpret its findings as proof that being overweight is ‘healthy’ – rather it may be slightly less unhealthy than perceived.


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