Which is worse, ecologically speaking: Lettuce or bacon? We know what veggie activists — not to mention a majority of consumers — would say. But are they right?

A new study done by Carnegie Mellon University researchers certainly came to some eye-opening conclusions, namely that a vegetarian diet could cause more harm to the environment than the “standard” diet that includes red meat and poultry.

In fact, according to news research from the Pittsburgh-based university, “Following the USDA recommendations to consume more fruits, vegetables, dairy and seafood might be more harmful to the environment” because those foods generate relatively high resource usage and higher greenhouse gas emissions.

“Eating lettuce is over three times worse in greenhouse gas emissions than eating bacon,” said Paul Fischbeck, the study’s lead and a Carnegie Mellon Professor of Social and Decision Sciences. “Lots of common vegetables require more resources per calorie than you would think. Eggplant, celery and cucumbers look particularly bad when compared to pork or chicken.”

That sounds wildly positive for the 310 million Americans who aren’t (self-described) vegetarians, but hold on a moment. Even when it’s good news, sound science — not to mention good journalism — requires that we look at the facts and live with the truth.

So before you break into the Hallelujah Chorus' from Handel’s Messiah, let’s look at the facts.

Fischbeck, along with Carnegie Mellon colleagues Chris Hendrickson, Professor of Civil and Environmental Engineering, and Michelle Tom, a Ph.D. candidate in Civil Engineering, deserves some credit for knowing how to make the media salivate in crafting the news release touting their research results.

However, a closer reading of their data paints a different picture.

Blue, green and gray

The researchers compared three different dietary scenarios: one that reduced calories without shifting the mix of food choices; one that shifted the “typical American diet” to the recommended USDA diet; and a third one that reduced calories while shifting to the recommended USDA diet.

As they noted in their study, which was published in Environment Systems and Decisions, that third scenario “increases energy use by 38%, blue water footprint by 10%, and GHG emissions by 6%.”

A quick note on the term blue water. It’s used to denote the water drawn from rivers, lakes and wells for residential and commercial use. In calculating a true water footprint, however, the calculation also has to include “green water,” the water drawn from soil in growing crops, and “gray water, which is the wastewater produced in manufacturing and processing operations.

Take beer, for example. You need water to brew it, of course — in fact, you need super cold runoff from a Rocky Mountain glacier if you want your beer to be the brand preferred by a bunch of 20-something models hired by an ad agency to have fun hanging out at a nightclub or sitting around on a deserted beach while holding bottles of your product.

But that pure mountain water actually represents only about 6% of the beer’s total water footprint. Of the approximately 300 gallons of water needed to produce one gallon of beer, only 18 gallons of blue water are used in brewing. The green water required to grow the grain and the hops that are fermented during production represent about 85% of the water footprint, with the remainder being the gray water discharged from the bottling plant as wastewater.

And here’s the reason that this study’s dramatic findings need to be evaluated cautiously. As the authors stated, “These perhaps counterintuitive results are primarily due to USDA recommendations for greater caloric intake of fruits, vegetables, dairy, and fish/seafood, which have relatively high resource use and emissions per calorie (italics added).

That’s the source of the researchers’ assertion that lettuce is worse than bacon. A pound of lettuce contains about 48 calories and requires 15 gallons of water to produce, whereas a pound of bacon contains 2,077 calories and requires 1,630 gallons of water to produce.

That means lettuce produces 0.31 calories of food energy per gallon of water, versus 0.78 calories per gallon of water for bacon.

Not quite three times as much, but close.

The point being that lettuce doesn’t necessarily generate substantially greater environmental footprint than bacon, only that the comparisons activists use to make meat products seem vastly more impactful on overall water, energy and resource use are seriously misleading. As is pretty much all of their propaganda.

However, regardless of this study’s spin, next time I’m dining out, the idea that lettuce is three times worse than bacon gives me a brand new reason to order the classic BLT.

Dan Murphy is a food-industry journalist and commentator.