From: Smigrodzki, Rafal (SmigrodzkiR@msx.upmc.edu)
Date: Thu Jun 20 2002 - 15:56:09 MDT
Hal Finney [mailto:hal@finney.org]:
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.
### The study mentioned by Doug seems to neglect the influence of obesity on
fitness - obesity per se and the conditions caused by obesity tend to reduce
your performance on the treadmill. If you take a cohort and allow a subgroup
to become obese, this will increase the frequency of diabetes,
hypercholesterolemia, and vascular disease (the proportion of sick
individuals) (see [2], although this is not an interventional study), and at
the same time decrease the level of fitness, on average [2], and in the
sickest persons in particular. Yet, there will be some outstandingly
resilient (and maybe lucky individuals) who will not be affected by the
conditions I mentioned above, and, not surprisingly, will maintain a good
level of fitness. If you look exclusively at their survival, instead of
analysing the whole cohort, you will not find a high mortality, because you
already excluded those who are most likely to die. It is then erroneous to
say obesity increases risk of death *only* in unfit subjects - because
obesity is the *cause* of reduced fitness, it does reduce survival, if
averaged over the whole obese cohort. You can't cherry-pick the fat people
to find the healthy ones and then claim that being fat won't make you sick.
A remark - the 3rd study I quote controls for each other of the risk
factors, and approaches the BMI and fitness level differently. Specifically,
they divided the subjects according to level of self-reported physical
activity, as opposed to treadmill performance. Only moderate activity
improved survival - and this is compatible with self-selection of sick
subjects to the inactive group, while vigorous activity did not further
improve survival. As long as you are healthy (and not too fat), you are
likely to be at least moderately active, and this is all you need to survive
the longest.
Rafal
References:
1. Allison DB. Zhu SK. Plankey M. Faith MS. Heo M. Differential associations
of body mass index and adiposity with all-cause mortality among men in the
first and second National Health and Nutrition Examination Surveys (NHANES I
and NHANES II) follow-up studies. [Journal Article] International Journal of
Obesity & Related Metabolic Disorders. 26(3):410-6, 2002 Mar.
UI: 11896498
* *
2. Wei M. Kampert JB. Barlow CE. Nichaman MZ. Gibbons LW. Paffenbarger RS
Jr. Blair SN. Relationship between low cardiorespiratory fitness and
mortality in normal-weight, overweight, and obese men. [Journal Article]
JAMA. 282(16):1547-53, 1999 Oct 27.
UI: 10546694
* * *
3. Lifestyle and 15-Year Survival Free of Heart Attack, Stroke, and Diabetes
in Middle-aged British Men
S. Goya Wannamethee, PhD; A. Gerald Shaper, FRCP; Mary Walker, MA; Shah
Ebrahim, FRCP
Background To examine the relationship between modifiable lifestyle factors
(smoking, physical activity, alcohol intake, and body mass index [BMI]) and
the likelihood of 15-year survival free of major cardiovascular end points
and diabetes in middle-aged men.
Methods A prospective study of 7142 men aged 40 to 59 years at screening
with no history of coronary heart disease, diabetes, and stroke drawn from 1
general practice in each of 24 British towns and followed up for 15 years.
Main Outcome Measures Death from any cause and a combined end point,
including survival free of heart attacks or stroke or the development of
diabetes over a follow-up of 15 years for each man.
Results During the 15-year follow-up, there were 1064 deaths from all
causes, 770 major heart attacks (fatal and nonfatal), 247 stroke events
(fatal and nonfatal), and 252 cases of diabetes among the 7142 men. After
adjustment for age and each of the other modifiable lifestyle factors, the
risk of the combined end point (death or having a heart attack, stroke, or
diabetes) went up significantly with increasing smoking levels and from BMI
levels of 26 kg/m2 or higher, and decreased significantly with increasing
levels of physical activity up to levels of moderate activity with no
further benefit thereafter (heavy smoking vs never: relative risk [RR]
[odds], 2.50; 95% confidence interval [CI], 2.12-2.94; BMI 30 vs 20-21.9
kg/m2: RR, 2.11; 95% CI, 1.71-2.62; moderate vs inactive: RR, 0.60; 95% CI,
0.50-0.72). Light drinking (vs occasional) showed a relatively small but
significant reduction in risk (RR, 0.84; 95% CI, 0.74-0.96). Using Cox
predictive survival models, the estimated probability of surviving 15 years
free of cardiovascular events and diabetes in a man aged 50 years ranged
from 89% in a moderately active man at BMI levels of 20 to 24.0 kg/m2 who
had never smoked to 42% in an inactive smoker with BMI level of 30 kg/m2 or
higher.
Conclusions Modifiable lifestyles (smoking, physical activity, and BMI) in
middle-aged men play an important role in long-term survival free of
cardiovascular disease and diabetes. These findings should provide
encouragement for public health promotion directed toward middle-aged men.
Arch Intern Med. 1998;158:2433-2440
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