Agriculture Reference
In-Depth Information
epidemic around, with attention to changes in social and physical environments as
well as individual behavior.
the emeRgence of obesIty As A globAl
PublIc heAlth PRoblem
At the same time that problems of undernutrition have not been solved in much of
the world, overweight and obesity have emerged in the last quarter century as major
public health problems globally. For most developing countries, there is thus now
a double burden of malnutrition with associated costs to health and quality of life.
More than a billion adults worldwide are now overweight, and a third of these are
overweight to a degree that classifies them as obese (World Health Organization
[WHO] 2003). The health consequences include premature deaths and chronic dis-
eases that reduce quality of life and threaten to overwhelm the resources of health
care systems widely. The impact on morbidity is greater than that on mortality, but
the latter is also substantial. The overall result is that, in major part due to rising
obesity, for the first time in history life expectancy at birth is expected to level off
and even decline in the first half of the twenty-first century (Olshansky et al. 2005).
In other words, there is a distinct possibility that the next generation may be the first
in recorded history to have shorter life expectancies than did their parents.
D
e f i n i n g
o
v e r w e i g h t
a n D
o
b e is i t y
Clinically,
obesity
is an amount of body fat, relative to lean tissue such as muscle
and bone, that is elevated to a level at which there are clear adverse effects on health.
Overweight
refers to a lesser degree of excess body fat, in spite of the fact that weight
is a unit of mass rather than body composition.
Because of ease of measurement and relatively good correlation with body com-
position, anthropometric measurements are most commonly used to determine the
prevalence of overweight and obesity. International definitions for adults are based
on the body mass index (BMI), which is calculated as weight in kilograms divided
by height in meters, squared (kg/m
2
), and multiplied by 100. This index is an expres-
sion of body weight (mass) adjusted for height and is at the population level a good
proxy for body fatness. At the individual level, there is variation; for example, a
football linebacker may have a high BMI but no excess body fat, and a sedentary
elderly woman might have a normal-range BMI but have excess body fat for optimal
health. But for populations, BMI is well correlated with body composition across a
wide range and provides a simple index that enables epidemiological comparisons
across populations. Internationally used diagnostic criteria for adult obesity (BMI
>
30) and overweight (BMI 25-29.9) are widely used in nutritional surveillance. These
cutoffs are conservative since there is evidence that risk of chronic disease in some
populations increases progressively from a BMI of about 21 (Popkin 2004).
For children, definitions are less clear and simple, at least in part because during
childhood the distribution of BMI varies with age. In the United States, the Centers
for Disease Control and Prevention (CDC) published age- and sex-specific reference
