Is Lettuce Worse for the Environment Than Bacon?

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A recent study and the flurry of media coverage surrounding it seems to suggest a truly puzzling conclusion: “Eating lettuce is more harmful to the environment than eating bacon.” How is this possible?? Let’s find out…

As the general assumption (supported by numerous previous studies) is that a meat-heavy diet is much more damaging to the environment than a more plant-oriented diet, these shocking recent headlines came as a surprise to many.

Based on a study by Carnegie Mellon University, which discusses the different environmental impacts of growing different fruits and vegetables, a sensationally worded press release published on December 14th, 2015 suggested that “Vegetarian And ‘Healthy’ Diets Could Be More Harmful To The Environment”.

The truth in fact, is not at all well-represented by this title, as the article below explains. BUT, as it also notes, there are some interesting and thoughtful discussions about taking a more holistic look at our eating habits that can come from even the most poorly-worded piece of news….

Michelle Tom co-authored the Carnegie Mellon study, originally titled “Energy use, blue water footprint, and greenhouse gas emissions for current food consumption patterns and dietary recommendations in the US.” That report, which looks into the environmental effects of different types of food, was retitled “VEGETARIAN AND “HEALTHY” DIETS COULD BE MORE HARMFUL TO THE ENVIRONMENT” by Shilo Rea, a director of media relations at the university, where Tom is a Ph.D candidate…
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“I think the title of this press release is definitely misleading and is not an accurate portrayal of our research,” Tom told me yesterday by phone. …

What Does the Study Say?

After drilling down through the study and talking to Tom and to Olson-Sawyer, here’s my understanding of what the study is actually trying to say: Not all vegetables and fruits have an equal impact on the environment (it looks at water use, energy use, and greenhouse gas emissions), and it’s even true that with some very careful rejiggering, you can create a possible produce-heavy diet that is worse for the environment than a meat-heavy one.

In her study, Tom sets up three possible scenarios, all related to the current caloric intake of the average American (they figured this at about 2,390 calories per day on average, with about half again that much in food waste) and the United States Department of Agriculture’s (USDA) recommendations regarding the percentages of each food group (grains, fruits, meats, vegetables, dairy) we should be eating….
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Lettuce vs Bacon: The Final Debate

The press release, and the coverage that followed, relied heavily on one very weird comparison: lettuce and bacon. This seems to come from one quote given by Paul Fischbeck, one of Tom’s advisers: “Eating lettuce is over three times worse in greenhouse gas emissions than eating bacon,” he said, according to the release….
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Regardless of Tom’s misgivings, you can see why a media person might have grabbed on to this—the two items fairly scream “healthy” and “unhealthy.” But to compare them using the information provided by this study is…insane. The study is in fact not saying anything of the sort, and the list of caveats needed to make that statement mathematically work would run pretty long. You’d have to compare them by calorie count instead of by weight or by nutritive benefits. You’d have to assume that any human would replace a protein source with a mostly water-filled leafy vegetable, which not even the USDA is recommending. (The USDA’s dietary guidelines do, in fact, include meat.) And you’d have to assume the figures on pork processing presented in the study are accurate, which I am not sure they are (given the lack of available data on full lifecycle emissions, which I’ll get into in a bit), and that the lettuce was grown in California….
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The Real Culprit is Not Lettuce

Tom told me that the basic point of her study was to demonstrate that not all fruits and vegetables are good for the environment and that not all meats are bad—but, in fact, even that is sort of irrelevant: The variable that really threw off the figures wasn’t the calorie counts in lettuce. The true X-factor in all this is sugars, fats, and oils. These items do not appear in either the abstract of the study (written by the scientists) nor in the press release, but a short interview with Tom was all it took to reveal that the true powerhouse in the equation, the high-calorie, low-impact foods that gave the study its conclusion, are these, and not lettuce. Tom wasn’t hiding it—the press release was, intentionally or not.
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When I asked if these categories—sugars, fats, and oils—had such a powerful effect on the calorie count that they would render any discussion of lettuce irrelevant, she laughed. “Well, yes. You are kind of right about that,” she said.

Of course that makes sense, if you look at it from a caloric perspective. (Which, by the way, not everyone thinks you should; Scientific American spoke to a researcher who advocates looking at the entire nutrient makeup of a diet rather than calorie count.) Sugars, fats, and oils have spectacularly high calorie counts by weight, meaning they’re “efficient” from that very specific perspective. And they’re also represented strongly in our current diet, rather than in the USDA’s recommendations. (The researchers, by the way, used the existing recommendations from 2010, not the new ones that should come out next year.) So it computes that of the three proposed scenarios, only the one that’s super high in sugars, fats, and oils would score high in caloric efficiency. Screw lettuce: This is a study about corn syrup and olive oil.

But is the Study Even Accurate?

Getting away from the problem of the press release for a minute, there are a whole mess of potential issues with the study itself. For one thing, when looking at the impact of certain foods on water use, it only examined “blue water” (referring to withdrawals from rivers, lakes, and groundwater), completely ignoring either “green water” (rain) or “grey water” (reused water)….

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…Olson-Sawyer notes that east of the Mississippi, green water is hugely important for agriculture. And California may be the country’s biggest agricultural state, but it’s nowhere near the majority…. In other words: California is important, hugely important, but there’s an awful lot of farming happening elsewhere. To ignore green water, which supplies a massive amount of water to thousands of farms, can totally throw off any water-use calculation.

Another issue: We all know that livestock produces lots of emissions… But as it turns out, we know basically nothing about the total greenhouse gas emissions involved in processing and packaging meat. “Since most of this is proprietary, it’s up to the business to share that information. The public doesn’t necessarily know what the environmental impact of processing is,” said Olson-Sawyer. A 2014 study from the University of Nebraska-Lincoln backs that up: The total greenhouse gas emissions of the whole life cycle of livestock, from breeding to raising to slaughter to packaging, is, basically, a mystery….

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This study is an interesting one, for sure; both Tom and Olson-Sawyer volunteered that, at its core, the report is a call for a more nuanced look at the way we eat and the way it affects the environment. Simply going vegetarian isn’t necessarily the answer, it says. In fact, there are (admittedly bizarre and unrealistic) ways that going vegetarian could actually be bad! But the study doesn’t suggest that vegetarianism is bad, or state that lettuce is “worse for the environment” than bacon. What it says, in a potentially flawed and messy but still valuable way, is that we have to think holistically about the way we eat, analyze it more thoughtfully and with a wider lens, if we want to have a positive impact.
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For the full in-depth analysis of the study, check out the original article at ModernFarmer.com.

 

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