The “6 percent body fat” meme seems to have originated in a 2010 interview with Mike Allen of Politico. Allen asked him about P90X—“a fad, a craze that you’ve created here on Capitol Hill.” Ryan, who says he once worked as a “fitness trainer,” talks about the workout group, which at the time he led with then-Rep. Bart Stupak (D-Mich.): “Tony Horton, the creator of it, comes by and works out with us every few months. It works because it’s called muscle confusion, it hits your body in many different ways—pull-ups, push-ups, sit-ups, lots of cardio, karate, jump training, yoga. So what it does is it pushes your body in many different ways so that it gets out of its plateau.”

Here’s who else maintains 6 to 8 percent body fat: Olympic 100-meter sprinters, that’s who. Also, world-class boxers, wrestlers, and marathoners, according to this study of elite American athletes. Top collegiate swimmers look pretty fit, right? Well, they average out at a plump 9.5 percent, at least according to another study. Positively porky, compared to Ryan. (For some perspective, the average man has body fat of 17 to 24 percent, and most women a bit more.)

For whatever reason, Paul Ryan likes to brag about how fit he is, and seems to have told a big fat fib about his running skills. I remember running for class president in high school and claiming to have killed a man in Frisco just to watch him die. Didn’t do it. But everyone believed it. Lost the election but got two weeks detention and a special notation in my “permanent record.”

Now, having been the managing editor of Men’s Fitness, I know there are several ways to measure body fat:

Calipers: Good luck getting the same result twice, which will depend on how many sites on the body you use, the caliber of the calipers, AND the reliability of the person doing the pinching and measuring.

Electrical impedance: Every Sears and Bed Bath & Body sells one of those scales that runs an electrical charge up your leg (not unlike the one that runs up Chris Matthews’s whenever he thinks of the president) and determines how much water your body is carrying. Because muscle is mostly water, an algorithm (my generic term for a buncha equations that turn one set of numbers into a “conclusion” that is meaningful to someone) takes the quantity of drippy stuff and translates it into body fat percentage. Hydration is key here. Weigh yourself first thing in the morning, when your system tends to be dehyrated, and you’ll cry. Food and alcohol intake, wet hair, sweat, all kinds of factors, mess with the numbers. Wildly.

Underwater weighing: What I call the Eureka! method. This was considered the standard, especially for athletes. The subject basically holds his or her breath and is dunked in a tub of water. It’s all about volume displacement and the fact that your fat cells are composed of triglycerides that have a fixed density. It’s probably the third most accurate method of measuring body fat. The second is:

DEXA: Basically a whole-body X-ray.

And the most accurate method of measuring body fat:

Autopsy: Unfortunately, not much you can do with the results. But it is something your loved ones can brag about, and even consider putting on your headstone.

Which is a really, really long way of saying: One man’s 6% body fat is another man’s 12—without either necessarily being a lie.

But then again, lying is what politicians do.

P.S. Tried P90X. If you want to get from 12% bodyfat to 6, then go for it. The trick is staying there.