A research team from Michigan State University
and Saginaw Valley State University measured the BMI of more than 400
college students - some of whom were athletes and some not - and found
that in most cases the student’s BMI did not accurately reflect his or
her percentage of body fat.
The research is published in the March issue of Medicine and Science
in Sports and Exercise, the official journal of the American College of
Sports Medicine.
BMI is determined by this equation: A person’s weight divided by his
or her height squared. Generally a BMI of 25 or above indicates a
person is overweight; 30 or above indicates obesity. A person with a
higher BMI is thought to be at a greater risk of heart disease,
diabetes and other weight-related problems.
“The overlying issue is the same criteria for BMI are used across
the board,” said Joshua Ode, a Ph.D. student in the MSU Department of
Kinesiology and an assistant professor of kinesiology at Saginaw
Valley. “Whether you’re an athlete or a 75-year-old man, all the same
cut points are used.”
“BMI should be used cautiously when classifying fatness, especially
among college-age people,” said Jim Pivarnik, an MSU professor of
kinesiology and epidemiology. “It really doesn’t do a good job of
saying how fat a person really is.”
The problem, especially among younger people and athletes, is that
BMI does not distinguish between body fat and muscle mass, said Ode.
“A previous study of NFL football players found that a large
percentage of them - around 60 percent - were considered obese,” he
said. “But when you look at an athlete like that, you see that in many
cases he is not obese. Many athletes have huge BMIs because of muscle
mass, but in many cases are not fat.”
The answer, said Pivarnik, is instead of having one cutoff point for
everyone, perhaps have different classifications for different people.
“Is a BMI of 25 for overweight and 30 for obese the right ones to
use with 20- to 29-year-olds in terms of disease risk?” he asked.
“Maybe it could be as simple as this: If you’re a regular exerciser or
an athlete, maybe 28 is overweight for you and 33 is considered obese.”
BMI, said Pivarnik, is used as a “surrogate” for percent fat, even though body fat doesn’t really fit into the equation.
“What if you take fat out of the equation?” he said. “Is there
something unique about BMI that may increase a person’s risk of chronic
disease, unrelated to fatness? Are people with high BMIs but low
fatness as much at risk of heart disease as other people? The answer is
no one knows.”
In their research, Ode and Pivarnik used carefully measured height
and weight to calculate BMI in more than 400 college-age people. They
then used a standard method of measuring body fatness and found that
BMI was not providing an accurate portrayal of the amount of fat a
student had.
Other members of the research team included Mathew Reeves, an
associate professor of epidemiology at MSU, and Jeremy Knous, a Ph.D.
student in the MSU Department of Kinesiology.
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