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MATT KALIL, A MAN ROUGHLY THE SIZE of a Kodiak bear, is sitting across the table from me in the Vikings' cafeteria at training camp, eating his lunch with all the enthusiasm of an assembly-line robot. Covering his plate are mounds of chicken Alfredo and penne pasta, piles of carrots and bell peppers and a stack of french fries the size of apple wedges. A thick piece of buttered garlic bread sits atop the pyramid, as if to taunt him. Over the next 30 minutes, much of that food will disappear one mechanical bite at a time.

When he's not chewing, Kalil is trying to convince me, despite my skeptical glances, that if he were to stop playing football, he could drop weight in no time. "If I just ate a regular diet," he says between bites of garlic bread, "like 3,000 calories a day, I could probably drop 20 pounds in two weeks. Easily. I weighed 312 pounds this morning, but I'm at 17 percent body fat."

Right now, however, Kalil is choking down 7,000 calories each day, which is fairly typical for a growing NFL lineman. In the trenches, it's all about getting leverage on the guy on the other side of the ball, and being bigger than him is perceived as the way to do it. That's why the last four decades have seen a huge increase in huge linemen. They're called the Big Uglies, and we now take for granted that they pretty much all tip the scales at three bills or more. But for many of them to reach that weight, it's a never-ending battle to the bulge, and there's a definite downside to that mass consumption.

Not that anyone is overly concerned about a bunch of big guys who are forced to eat a lot. Concussions and suicides are the NFL's hot-button issues. The largest men on the field are often invisible; after all, they don't carry the ball or score touchdowns. So while the league and the media are in a frenzy over bounties and chronic traumatic encephalopathy (CTE), there has been no hysteria over the fate of the Uglies. This despite the fact that a recent National Institute for Occupational Safety and Health study determined that NFL players with a body mass index (BMI) of 30 or more during their careers, meaning they were clinically obese, are twice as likely to die of heart disease as their teammates.

Just starting his NFL journey, the 23-year-old Kalil, the fourth pick in the draft, is concerned only with keeping on the weight he's working so hard to add. The left tackle is blessed with the kind of blazing metabolism most of us would kill for. Which is why every night, regardless of what he's eaten that day, Kalil must down a 1,200-calorie protein shake. To get the chalky liquid down, he blends in peanut butter. Nights after a big dinner out with friends, Kalil will return home and stare at the shake in silent misery. Imagine adding a loaf of bread to an already full stomach. And if he drinks the grainy gunk too soon before bed, it will give him painful acid reflux and keep him awake for hours -- as if his digestive system is staging a revolt.

None of this is new to Kalil. It's been his routine for years. That's how NFL linemen are built nowadays -- one protein shake at a time. When Kalil was 15, he showed up for his first football practice at Servite High School in Anaheim, Calif., and expressed interest in playing tight end. But his father, Frank, a former collegiate lineman who'd had a brief career in the USFL, walked up to his son's coaches and put an end to the fantasy. "Sorry," Frank said, "but my son is a left tackle."

That's the position Frank had trained Matt to play, drilling him on slide steps and blocking technique at the park near their house. At the time, NFL tight ends weren't the size of Rob Gronkowski, so Matt put away his dream and joined the linemen. And every day since that first high school practice, people have been shoving large plates of food in front of him. "It's always been about me gaining weight," Kalil says. "My dad was like, 'Did you eat today? What do you weigh?'"

It's still a constant refrain. Kalil was an All-America tackle for Southern Cal, a 6'7", 290-pound bulldozer with ballerina feet, the kind of lineman every NFL general manager dreams of plugging into his lineup so he can sleep better on Saturday night. But when Kalil decided to forgo his senior year at USC and enter the draft, he spent five months hearing one thing over and over from coaches, analysts and experts: You'll need to put on more weight if you want to be an elite lineman. Says Kalil, "Every question I got at the combine was, 'So, how much do you think you could weigh?'"

NFL lineman is one of the only jobs in the world, along with maybe sumo wrestler, for which an employer can look at a 300-pound man and suggest, with a straight face, that he's undersize. Hall of Fame left tackle Anthony Munoz -- who, like Kalil, played at USC and was a top-five draft pick -- played his entire Bengals career, from 1980 to 1992, at 278 pounds. That would be impossible today as linemen continue to get bigger. In 1970, there was one NFL player who weighed 300-plus pounds. Last season, there were 360.

So how exactly did a 280-pound lineman become a lightweight? There's little doubt that the rise of performance-enhancing drugs was a factor. Steroids allow athletes to increase muscle mass and train longer and with more intensity, the perfect formula for a player looking to pack on pounds and gain an edge on the line of scrimmage. Though the NFL has one of the strictest testing programs in all of sports, a confidential survey published in 2009 by the Center for the Study of Retired Athletes at the University of North Carolina at Chapel Hill revealed that nearly 1 in 10 former NFL players admit to having used steroids. More than 20 percent of players from the 1980s admit to having used them. That number has dipped to 13 percent, but among the offensive linemen surveyed, 16 percent admit to having used PEDs.

That means the vast majority of players are getting bigger naturally, through diet and weight programs that have become more sophisticated and precise in the past three decades. "I went to high school in the '70s, and I never lifted weights until I got to college," says Titans coach Mike Munchak, a former guard and nine-time Pro Bowl selection with the Houston Oilers. "Now high schools have year-round weight-training programs. You're seeing guys develop sooner. When I got to the Oilers in 1982, there wasn't an offseason program. Guys just didn't make enough money. They were doing other jobs."

Munchak can still remember when he heard that a few NFL players had crossed the 300-pound threshold. "I thought, Oh my gosh, we've reached the limit here," he says. "I thought, Well, we've really maxed out. I just can't imagine guys getting much larger."

Up close, Kalil's chest looks like the hull of a small...