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different people will suffer health impairments at different levels of weight,
tools like BMI are just the start of the
diagnostic
process. Doctors also con-
sider symptoms like breathlessness, fatigue, blood pressure, resting heart
rate, swelling in the legs, accumulations of body fat noted via the “eyeball
test” (that is, their observational skills), and other factors when determining
whether a person is a healthy or unhealthy weight.
To understand the limitations of BMI alone as a diagnostic tool for deter-
mining healthy body size, think about the following two cases:
Andrew is five feet, five inches tall and weighs 155 pounds. He’s the
star of the swim team, sporting muscular shoulders, upper arms, and
thighs. To look at him, you’d think he didn’t have an ounce of body fat.
His trim physique is toned and firm, and his cardiovascular endurance
is unbelievable; he can swim 500 meters with ease.
Jonathan is the class geek and proud of it. He scored 1450 on the
SATs, and he’s a computer genius who spends hours at his keyboard.
At five feet, seven inches and 155 pounds, he’s slim but couldn’t run a
mile if his life depended on it. Just going upstairs to math class leaves
him winded! The word exercise is definitely not in his vocabulary, and
his body shows it; his abdomen is soft and wrinkly, and his thighs,
thin as they are, jiggle.
One day Andrew and Jonathan calculate their BMIs as part of a
health project. Jonathan’s is 24 (in the “normal” range), but Andrew’s
BMI is 28 (in the overweight range). If people looked solely at these
numbers to determine these boys’ health, they’d say Jonathan was in
better physical condition than Andrew. But he’s not. How can this be?
Andrew and Jonathan illustrate an important lesson about BMI: It is not
the sole indicator of health. It is just one of many indicators, including diet,
physical activity, waist circumference, blood pressure, cholesterol levels, fam-
ily history, and blood sugar. Because muscle tissue is much heavier than fat
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