By now, most folks have reviewed the recent Carnegie Mellon University study that boldly stated, “Lettuce Produces More Greenhouse Gas Emissions Than Bacon Does: A vegetarian diet does not necessarily have a low impact on the environment.”

(Well, at least they noticed that provocative headline. Honestly, I’ve yet to find anyone who confirms that they actually read the study — me included; I relied on the summary published by Scientific American).

For anyone connected to animal agriculture, the takeaway from the study was pretty straightforward: Bacon is way better than lettuce. Taste-wise, that’s entirely true.

But the more important conclusion, which was referenced in the second part of that headline above, was that embracing the diet recommended by USDA’s Dietary Guidelines could result in as much as a 38% increase in energy use, a 10% increase in water use and a 6% increase in total greenhouse gas emissions.

That doesn’t imply that a meat-centric diet is healthier; only that incorporating a greater amount of fruits and vegetables in one’s daily diet would not be without consequences as far as energy use and resource allocations are concerned.

Two reasons for that.

First, the Carnegie Mellon study took into account what the total lifecycle of a food product: cultivation, irrigation, harvesting refrigerated transport, retail sales and overall shrink, or waste. On that score, bacon wins hands-down, because very little of the product is lost due to spoilage or consumer-level waste.

The second reason that lettuce looks so bad, comparatively speaking, is because of a concept which most consumers are vaguely familiar, but one that typically gets obscured amidst all the anti-industry bashing that surrounds livestock production, is nutrient density. Fruits and veggies look worse than meat products in comparing energy and water use, but only on a per-calorie basis.

In other words, it takes more energy and water to produce one calorie of lettuce than it does to produce one calorie of meat — because an entire head of lettuce only provides about 75 calories. That’s almost exactly what you get with the two small, cooked slices of bacon found on a typical foodservice BLT.

But let’s not jump to hasty conclusions here, as the researchers themselves cautioned.

“You cannot assume that any vegetarian diet is going to have a low impact on the environment,” Paul Fischbeck, a professor of Social and Decision Sciences and Engineering and Public Policy and one of the authors of the study, told Scientific American. “There are many that do, but not all. You can’t treat all fruits and veggies as good for the environment.”

In their study, the researchers concluded that fruits have the largest water and energy footprint per calorie, whereas meat and seafood have the highest greenhouse gas emissions per calorie. Neither is eco-neutral, so to speak.

Analyzing the whole diet

So what does this mean for the “typical” American diet, as recommended by the nutrition community? What should we be eating, if environmental protection were truly our primary concern?

Which it’s not, by the way. Even hardcore vegans flock to recipes and food choices that taste the best — just like their carnivorous cousins.

The short answer: The foods that few people. Vegetarian or otherwise, regularly consume: kale, okra, broccoli and Brussels sprouts, for starters.

Even born-again veggies rarely plan a meal around those foods.

There’s on other point that should temper the “bacon is better than lettuce” meme, and that involves a study done by a University of Michigan team led by Martin Heller, a research specialist at the university’s Center for Sustainable Systems. They concluded that if Americans actually followed the USDA Dietary Guidelines, they’d eat less meat, which would reduce GHG emissions, but would drink more milk, which would offset those reductions.

Ultimately, the bottom line is one that dieticians have been preaching for generations — eat a balanced diet, one that includes, not excludes, meat, dairy, fruits, vegetables, whole grains and legumes.

Let’s heed the insights that Prof. Fishbeck’s study provided, as Scientific American phrased it, that “the best diet for the environment would be terrible for a person’s health.”

“Which diet would have best impact on the environment?” Fischbeck told the magazine. “You’d eat a lot more fats and sugars.”

Um, professor. I think we’re already there. 

Dan Murphy is a food-industry journalist and commentator