From: Hal Finney (hal@finney.org)
Date: Thu Jun 20 2002 - 11:16:16 MDT
There are a number of studies which show that obesity per se is not a
health hazard. Doug Skrecky posted here about a large study involving
over 20,000 men, which found that fit, obese men had essentially no
more mortality risk than fit men of normal weight.
http://www.extropy.org/exi-lists/extropians.3Q99/1533.html
One table which Doug reproduced:
Table 3
Waist circumference category Multivariate RR
and cardiorespiratory fitness level of death
Low waist circumference (<87 cm)
Fit 1.0
Unfit 4.88
Moderate waist circumference (87 to <99 cm)
Fit 1.05
Unfit 2.05
High waist circumference (>99 cm)
Fit 0.95
Unfit 2.40
The RR is the relative risk, higher numbers are worse. Clearly being
unfit is the real concern.
Here is another table I found online, from
http://www.iom.edu/iom/iomhome.nsf/WFiles/blairrev/$file/blairrev.ppt.
(This is a PowerPoint slide presentation.) It shows data from a study
of 24,335 men, relative risk based on BMI and number of additional risk
factors. Risk factors would include such things as smoking, diabetes,
family history, etc.
BMI Number of risk factors
0 1 2 3 >=4
18.5-24.9 1.0 1.2 1.7 2.1 3.5
25.0-29.9 1.0 1.2 1.8 2.6 4.8
>=30.0 0.9 1.1 2.3 3.0 5.3
The rows correspond to normal weight, overweight, and obese. Clearly
obesity is a problem primarily when two or more risk factors are present.
Now, in fact, most overweight people are unfit. There are many obvious
reasons with causation in both directions for this effect. I think this
is the real reason why obesity is generally associated with increased
mortality in studies which don't distinguish groups by fitness.
The lesson from these kinds of studies is unfortunately not being applied
in public health recommendations. People are consistently advised
to lose weight. But empirical results show that it is very hard for
people to lose weight and keep it off. And some results suggest that
failed attempts to diet (yo-yo dieting) may be even worse for you than
not dieting at all. If most dieting attempts fail, this means that the
conventional advice is actually hurting people's health.
It might be better to advise people to get fit. I think it's a lot easier
to get fit than to lose weight. (Unfortunately, getting fit does not
automatically cause you to lose weight.) People can include a daily
30-minute walk (weather permitting) and many will find it relatively
enjoyable after a while. Few people enjoy dieting.
Hopefully in the next couple of decades we will have a better
understanding of obesity and there will be safe medications that allow
everyone to weigh whatever they want. Until then the main lesson should
be that even overweight people who have given up on losing weight can
still work on getting fit. This will give them many of the same health
benefits as losing weight.
Hal
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