The current BMI weight guidelines were adopted by a National Institutes of Health panel in 1998, based on previous WHO guidelines and on studies linking obesity to health problems, according Barbara Hansen, a member of the NIH panel and a professor of physiology at the University of Maryland School of Medicine.
Under previous rules, anyone with a Body Mass Index of 26 or above was simply classified as "overweight." The 1998 recommendations - released with little fanfare but distributed to doctors and researchers nationwide - lowered the pudginess threshold to 25, thereby adding 25 million people to the 72 million adults previously considered overweight. And it added 30 as a threshold for true obesity.
Hansen said the panel wanted to keep things simple: "First of all, it's a nice round number for obesity - 30. And it's approximately at that point where the studies showed one should seriously consider the increasing likelihood of being susceptible to certain diseases."
By setting the "overweight" threshold at 25, BMI provides an early warning for people to watch their weight, she said. Although athletes and others with large muscles are the exception to the rule, she added, statistically they are a tiny minority.
"We're talking about a very small number of people who may be exceptions," she said. "It's a good estimate for the population. It's not precise for individual use, but it's really best as a loose guideline."
Experts say competitive athletes are susceptible to high BMI scores because of the increased muscle that comes with conditioning. "Guys with incredible muscle mass are just going to weigh a lot more," said Dr. Andrew Tucker, director of sports medicine at Union Memorial Hospital and head physician for the Ravens.
University of North Carolina researchers reported in the Journal of the American Medical Association last month that 56 percent of the players in the NFL are obese, and Tucker said the NFL is examining the findings.
But he acknowledged that the game does reward players with increased size - particularly if they're lineman. "Their focus is function on the field, and if you're a linemen, those are positions that reward mass," he said.
"Are the rules promoting an unhealthy body type? Some people think so," he added, "but we really need sound science before we use that rationale to change the rules."
Even for those who are not NFL material, the federal BMI guidelines may seem unduly harsh. For example, a person who is 5 feet 10 inches tall and weighs 181 pounds has a BMI of 26 and is classified as overweight. If that person gains 25 pounds, his BMI closes in on 30 - which would make him obese.
And that's the point, says Michael Fumento, a senior fellow at the Hudson Institute in Washington and author of Fat of the Land. He sees the BMI guidelines as an early warning system for waistline creep.
"It can seem strict, but the fact is if your BMI is 23 at one point, and a year later, is at 24 or 25, it really isn't because you're exercising more," he said.
To calculate your body mass index online, visit www.baltimoresun.com/bmi.
What's your BMI?
BMI, Body Mass Index, is calculated by dividing a person's weight by height. Standards adopted by the National Institutes of Health in 1998 say that anyone with BMI of 25 or above is overweight and anyone with a BMI of 30 or above is obese. The BMI is applied to adults over age 20.
To find your BMI, see the chart on Page 6A or use a BMI calculator online at www.baltimoresun.com/bmi