What is “the cheapest, most nutritious and bountiful food that has ever existed in human history” Hint: It has 390 calories. It contains 23g, or half a daily serving, of protein, plus 7% of daily fiber, 20% of daily calcium and so on.

Also, you can get it in 14,000 locations in the US and it usually costs $1. Presenting one of the unsung wonders of modern life, the McDonald’s McDouble cheeseburger.

The argument above was made by a commenter on the Freakonomics blog run by economics writer Stephen Dubner and professor Steven Levitt, who co-wrote the million-selling books on the hidden side of everything.

Dubner mischievously built an episode of his highly amusing weekly podcast around the debate. Many huffy back-to-the-earth types wrote in to suggest the alternative meal of boiled lentils. Great idea. Now go open a restaurant called McBoiled Lentils and see how many customers line up.

But we all know fast food makes us fat, right? Not necessarily. People who eat out tend to eat less at home that day in partial compensation; the net gain, according to a 2008 study out of Berkeley and Northwestern, is only about 24 calories a day.

The outraged replies to the notion of McDouble supremacy — if it’s not the cheapest, most nutritious and most bountiful food in human history, it has to be pretty close — comes from the usual coalition of class snobs, locavore foodies and militant anti-corporate types. I say usual because these people are forever proclaiming their support for the poor and for higher minimum wages that would supposedly benefit McDonald’s workers. But they’re completely heartless when it comes to the other side of the equation: cost.

Driving up McDonald’s wage costs would drive up the price of burgers for millions of poor people. “So what?” say activists. Maybe that’ll drive people to farmers markets.

For the average poor person, it isn’t a great option to take a trip to the farmers market to puzzle over esoteric lefty-foodie codes. (Is sustainable better than organic? What if I have to choose between fair trade and cruelty-free?) Produce may seem cheap to environmentally aware blond moms who spend $300 on their highlights every month, but if your object is to fill your belly, it is hugely expensive per calorie.

Junk food costs as little as $1.76 per 1,000 calories, whereas fresh veggies and the like cost more than 10 times as much, found a 2007 University of Washington survey for the Journal of the American Dietetic Association. A 2,000-calorie day of meals would, if you stuck strictly to the good-for-you stuff, cost $36.32, said the study’s lead author, Adam Drewnowski.

“Not only are the empty calories cheaper,” he reported, “but the healthy foods are becoming more and more expensive. Vegetables and fruits are rapidly becoming luxury goods.” Where else but McDonald’s can poor people obtain so many calories per dollar?

And as for organic — the Abercrombie and Fitch jeans of food — if you have to check the price, you can’t afford it. (Not that it has any health benefits, as last year’s huge Stanford meta-study showed.)

Moreover, produce takes more time to prepare and spoils quickly, two more factors that effectively drive up the cost. Any time you’re spending peeling vegetables is time you aren’t spending on the job.

Activists will go anywhere to wave the banner of caring and plant their flagpole of social justice right in the foot of the working class.

Forcing New Yorkers to pay unnecessary high prices, they’ve managed to keep Walmart out of the five boroughs of New York City. The City Council of Washington, DC, recently passed a bill, designed specifically to punish only Walmart, which would mandate a super-minimum wage to benefit a small number of employees while effectively placing a surtax on every Walmart shopper. (Walmart responded by saying it was canceling plans for three stores. The bill may yet be vetoed by Mayor Vincent Gray.)

Fuel prices, like food prices, disproportionately hit the poor, so do-gooders do everything they can to raise energy costs by blocking new fuel sources like the Keystone XL pipelines and fracking. And they are always up for higher gasoline taxes and regulating coal-burning energy plants to death.

If the macrobiotic Marxists had their way, of course, there’d be no McDonald’s, Walmart or Exxon, because they have visions of an ideal world in which everybody bikes to work with a handwoven backpack from Etsy that contains a lunch grown in the neighborhood collective.

That’s not going to work for the average person, but who cares if they go hungry because they can’t afford a burger anymore? Let them eat kale!

kyle.smith@nypost.com