If you're Barry Allen, the superhero-in-disguise and star of the CW's hit show "The Flash," you can run at blinding speeds to save lives and do battle with evil metahumans.
But this amazing ability would require incredible energy expenditure, begging a practical question: How much food would The Flash have to eat?
To find out, Tech Insider spoke to James Kakalios, a physicist at the University of Minnesota and author of "The Physics of Superheroes."
We spoke to Kakalios for a previous post, which focused on the powers that Allen (played by actor Grant Gustin) would need to survive. But in this look at the science behind a favorite superhero, we dig into another important aspect of superspeed: Proper nutrition.
The number of calories we calculated that The Flash would need to eat shocked us. To understand how we got that number, though, we first need to look at how much food regular humans need to eat to run around.
The trouble with calories
Calculating the amount of calories a normal person burns is tricky, no matter what your treadmill may tell you.
An old rule used to be 100 calories per mile, regardless of speed. If you ran or walked a faster mile, the thinking went, you'd burn calories faster — but you'd also cover that mile in less time, balancing out calorie output.
That certainly makes the math easy. Unfortunately, "100 calories per mile" doesn't hold much weight. Moving at different speeds requires different strides and mechanics, and taxes the human body in different ways.
Runner's World's Amby Burfoot, who won the 1968 Boston Marathon, debunked the 100-calorie myth in 2005, citing a study that found speed and gait really does matter when it comes to burning calories:
Running and walking aren't as comparable as I had imagined. When you walk, you keep your legs mostly straight, and your center of gravity rides along fairly smoothly on top of your legs. In running, we actually jump from one foot to the other. Each jump raises our center of gravity when we take off, and lowers it when we land, since we bend the knee to absorb the shock. This continual rise and fall of our weight requires a tremendous amount of Newtonian force (fighting gravity) on both takeoff and landing.
Faster strides require more force to overcome gravity, since you're staying airborne for longer, and our legs require more energy to absorb the opposing force when we hit the ground. Air drag becomes problematic, too.
Running faster also brings a person closer to "oxygen debt," which is when your body switches to burning energy reserves in your muscles in the form of glycogen. Your muscles can take days to replenish glycogen, so once you hit this point (known as VO2 max) you can't stay at that pace for long.
Human metabolism is a complicated process. Figuring out caloric output for a metahuman is even trickier (nay, impossible) — for example, how many more calories would The Flash have to burn to fight air drag at supersonic speeds?
It's moments like these when Kakalios reminds himself that it's a work of fiction. "Relax, kid, it's a comic book." He'll suspend his disbelief, he says, "as long as they play fair and don't add powers willy nilly."
How much it takes to power The Flash
The canon explanation for Allen's energy source for superspeed is "the speed force:" a mythical, other-dimensional source of power tapped by him and other DC Comics speedsters. But we'll table that convenient plot device and try to get real.
So just how much would The Flash need to eat?
Snacking all day wouldn't cut it. And the specially baked energy bars that his friend Cisco Ramon bakes couldn't possibly pack enough energy, barring some wormhole-caloric-transport-situation inside the food.
Kakalios provided us with a rough estimate that gets at the scale of just how much food Barry Allen would have to put away, and it's nuts.
"He'd have to eat 200 million cheeseburgers to run at superspeed once," he said.
How many calories are in 200 million cheeseburgers? Obviously it varies, but let's use the closest thing to a single unit of cheeseburger: one from McDonald's.
A McDonald's cheeseburger has about 300 calories, so 200 million of them would provide you with 60 billion calories. And assuming 4 ounces per burger, that meal would weigh 7.5 million tons. That's equal to 15 Burj Khalifas — the world's tallest building — made of cheeseburgers.
And putting aside the issue of stomach real estate, eating that many calories (and burgers) would also pose a different kind of food expenditure problem. Kakalios put it simply. "One word: elimination."
