It's no secret that size matters in the National Football League (search), but a new study suggests that a whopping 56 percent of NFL players would be considered obese by some medical standards.

The NFL called the study bogus for using players' body-mass index (search), a height-to-weight ratio that doesn't consider body muscle versus fat. The players' union said that despite the familiar sight of bulging football jerseys, there's no proof that obesity is rampant in the league.

But former defensive tackle John Jurkovic said he's seen plenty of evidence that players have gotten not just bigger but sometimes fatter, "big as houses" in recent years because of league pressure to intimidate opponents and win.

"The NFL teams want it because it's working," said Jurkovic, who played for Green Bay, Cleveland and Jacksonville before retiring in 2000.

The theory is that bigger men, especially linemen and defensive players, are better blockers and harder to move.

But the study results suggest that bigger players don't make a team more successful. There was no relationship between teams' average player BMI and their ranking in 2003-04, the season studied. Arizona had the highest average BMI but also the worst record in its division.

In the study, University of North Carolina endocrinologist Dr. Joyce Harp and student Lindsay Hecht used statistics on the NFL Web site to calculate BMIs for 2,168 NFL players, nearly all those playing in the 2003-04 season.

Almost all the players qualified as overweight, and 56 percent had BMIs of at least 30 — what doctors consider obese. For example, a 6-foot-2 man weighing 235 has a BMI of just over 30. Nearly half of the obese players were in the severely obese range, with a BMI of at least 35, and a small percentage were morbidly obese with a BMI of at least 40.

Harp acknowledged that without measuring body composition, it's uncertain how many players were truly fat, but she said it's unlikely the high BMIs were "due to a healthy increase in muscle mass alone."

"The high number of large players was not unexpected, given the pressures of professional athletes to increase their mass. However, it may not be without health consequences," the researchers wrote, citing previous studies that documented obesity-related problems, including sleep apnea and high blood pressure in NFL players.

The study appears in Wednesday's Journal of the American Medical Association.

While the study methods were not very scientific, players' growing girth "is a major concern," said Dr. Arthur Roberts, a former NFL quarterback and retired heart surgeon whose Living Heart Foundation works with the players' union to evaluate heart-related health risks faced by current and retired players.

"These larger body sizes are generally associated with greater cardiovascular risks," Roberts said.

The increasing emphasis on size may be a bad influence on "all the young kids that play football around the country ... and are trying to be like their heroes," Roberts said.

Players' union spokesman Carl Francis said health and safety are "discussed all the time," and that while some players likely are obese, it's not a major problem.

NFL spokesman Greg Aiello called the study substandard and said there's no proof obesity is worse in the NFL than in U.S. society in general, where about 30 percent of adults are obese, based on BMI data. "This was not a serious medical study," he said.

Dr. Brian Cole of Chicago's Rush University Medical Center, an orthopedic surgeon who works with the Arena Football League, also questioned the study methods and said some teams list inaccurately high weights to appear more intimidating.

"While clearly there are pressures for increased size" in professional football, relying on published height and weight data but not physical exams is faulty, he said.

Julie Burns, a nutritionist who works with the Chicago Bears, said combining BMI data with players' waist measurements is a better fat indicator because some highly conditioned athletes with a high BMI also have a large amount of lean tissue.

Jurkovic said he weighed 272 in the mid 1990s — hefty by any standards on his 6-foot-2 frame — but was pressured by a coach to get even bigger and ballooned up to 328. On the BMI scale, that's morbidly obese. Jurkovic said he had already maxed out on weightlifting so he packed on mostly fat by gorging.

Combined with the physical toll of football, excess weight wears down joints and causes problems as players age and then retire, Jurkovic said. At 37, he now weighs a "chunky" 295 and has ankle problems he blames on football and excess weight.

"It's tough for the league to police, but I think they should try to police it," he said.