Largest Meta-Analysis
Flegal et al (2013) conducted a meta-analysis of over 100
previously published research papers connecting body weight and
mortality risk among 2.88 million study participants living around
the world. Using standardized BMI
categories (WHO 1997) relative to those classified as normal
weight:
- Overweight individuals actually have a significantly lower
all-cause mortality.
- Those classified with Grade 1 obesity did not have higher
a mortality overall
- Those with Grades 2 and 3 obesity were associated with significantly
higher all-cause mortality
Possible explanations of these finding include:
- Overweight and obese people may get better medical care.
- Heavier people may have better survival during a medical
emergencies such as infections or surgery.
- Reverse causation, implying being sick can make you thin.
- Studies showing contrary results used a variety of different
BMI categories with different cut-points for the various weight
groups.
- Overweight people in theses studies who tend to live longest
may not be fatter than most people at all, but in fact average
weight, since 33% of U.S. adults are clinically overweight and
an additional 36% are obese.
Flegal KM, Kit BK, Orpana H, Graubard BI (2013). Association
of all-cause mortality with overweight and obesity using standard
body mass index categories: a systematic review and meta-analysis.
JAMA. 2013 Jan 2;309(1):71-82
Higher Mortality
Those who maintain their normal weight are less likely to
be killed in a car accident
New York Times, March 7, 2006, pg D6.
In the US, obesity accounts for between an estimated 0.30
and 1.08 years of population life expectancy at birth, depending
on gender, ethnicity, and severity of obesity
Olshansky SJ, Passaro DJ, Hershow RC, et al. (2005). A
potential decline in life expectancy in the United States in
the 21st century. N Engl J Med. 352,1138-45.
Obesity decreases life expectancy by six years, on average
(Cooper 2003).
Excessive body weight increases the risk of death from all
causes.
J Stevens, J Cai, ER Pamuk, DF Williamson, MJ Thun, JL
Wood (1998). The effect of age on the association between body-mass
index and mortality. New England Journal of Medicine, 338(1):
1-7.
Lower Mortality
The best mortality rates are those 25 to 30 percent over ideal
recommended weight (Gaesser, 1996).
Greater body fat has a protective effect against osteoporosis
(Felson, et al., 1993), lung cancer (Kabat & Wynder, 1992),
and breast cancer (Wallace, et al., 1982).
Weight loss for overweight individuals may fail to improve
health and can actually increase mortality rates (Andres, Muller
& Sorkin, 1993).
Thin under active men have 2.5 times the death rate than active
overweight men.
No Relationship
There is no clear-cut evidence substantiating obesity causes
poor health and reduced longevity (Gaesser, 1996; Ernsberger
& Haskew, 1987).
No relationship exists between body fat and degree of artheroscleritic
buildup in coronary arteries (Barett-Connner, 1995; Kramer, et
al., 1993).
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