Is eating lettuce really worse for the environment than bacon?

A recent study from Carnegie Mellon University in Pittsburgh entitled “Energy use, blue water footprint, and greenhouse gas emissions for current food consumption patterns and dietary recommendations in the US” has complicated the tidy narrative put forward by vegetarians that eating vegetables instead of meat would constitute a major reduction in greenhouse gases, water usage and resource wastefulness.

Not so fast, says the study. Your BLT sandwich is practically a weapons-grade emitter, combining both bacon and lettuce, compared to, say, a relatively more benign falafel.

“Eating lettuce is over three times worse in greenhouse gas emissions than eating bacon,” said Paul Fischbeck, professor of social and decisions sciences and engineering and public policy. “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.”

While the temptation may be great to shout, “Bacon! Yes! Screw you, vegetarians!” from the rooftops, the actual findings of Fischbeck’s study are a little more nuanced than “Vegetables bad, bacon good.”

The study, in fact, looked at the consequences of three hypothetical situations relative to the 2010 USDA Dietary Guidelines, which are “are intended to help individuals achieve and maintain healthy weight.”

So the study’s aim was to measure “the changes in energy use, blue water footprint, and greenhouse gas (GHG) emissions” that would result from a change in diet relative to USDA dietary guideline recommendations, which are less about reducing environmental impact than they are about reducing society-wide obesity.

Scenario 1 examined “reducing Caloric intake levels to achieve ‘normal’ weight without shifting food mix”, which resulted in a 9% decrease in energy use, blue water footprint, and GHG emissions.

Scenario 2 examined “switching current food mix to USDA recommended food patterns, without reducing Caloric intake”, which resulted in a 43% increase in energy use, a 16% increased blue water footprint, and an 11% increase in GHG emissions.

Scenario 3 examined “reducing Caloric intake levels and shifting current food mix to USDA recommended food patterns, which support healthy weight”, which resulted in a 38% increase in energy use, a 10% increased blue water footprint, and a 6% increase in GHG emissions.

So basically, the report is saying that a diet that values environmental concerns over personal health or obesity should not adhere more closely to USDA dietary guidelines, but should instead concentrate on taking in fewer calories, which after all require greater resources and energy usage per calorie.

“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,” write the paper’s authors.

In fact, what the study shows is that while a mass adoption of USDA guidelines may be good for the nation’s obesity rates, such a shift would be disastrous for the environment.

“There’s a complex relationship between diet and the environment,” said Michelle Tom, a member of the Carnegie Mellon team. “What is good for us health-wise isn’t always what’s best for the environment. That’s important for public officials to know and for them to be cognizant of these tradeoffs as they develop or continue to develop dietary guidelines in the future.”

That hasn’t stopped various click-baity news outlets, however, from trumpeting the study’s results as evidence that “Vegetarian and ‘healthy’ diets may actually be worse for the environment, study finds”.

On the other side of the ledger, vegetarians have believed for years, thanks to books like “Diet for a Small Planet” and ex-California governor Arnold Schwarzenegger speaking at the recent COP21 conference, that adopting a vegetarian diet is the best way to help the planet.

One can assume, however, that Schwarzenegger’s diet involves a whole lot of calories, and that eating broccoli instead of meat would be very much more damaging to the environment, especially to provide enough calories to feed a professional body builder.

As Tamar Haspal points out in the Washington Post, to replace a kilogram of beef, at 2,280 calories, you’d need 6.7 kilograms of broccoli.

First of all, nobody, even people who enjoy broccoli, are going to eat that much broccoli.

But when food is ranked by “emissions per calorie” rather than “emissions per kilogram”, tomatoes, broccoli and salmon are all worse offenders than pork, chicken and canned tuna.

And of course, the fact that lettuce on a per calorie basis is worse for emissions than bacon is not necessarily a total condemnation of lettuce, except in the case of that one idiot who’s trying to maintain a healthy weight on a lettuce-only diet.

What the Carnegie Mellon study says is that, to borrow a phrase from Facebook, “It’s complicated.”

If you were dreaming that vegetarianism was going to be your personal silver bullet solution to stopping climate change in its tracks, what this study says is that you’ll have to evaluate each food on a case-by-case basis.

Also, go ahead and eat some bacon. It’s fine, as long as your main diet consists of lentils, which rank top of the list for reduced environmental impact, according to Haspal’s list.

For a longer term solution, we’ll likely have to look at replacing store-bought meat with a lab-grown substitute, or eating bugs for protein.

A 2006 report by the United Nations Food and Agricultural Organization, called “Livestock’s Long Shadow”, concludes that 18% of annual global greenhouse gas emissions was caused by the methane emitted by livestock including cattle, sheep, pigs and poultry.

The Environmental Protection Agency says that methane from livestock constitutes one third of all annual agricultural emissions in the United States.

So, while you’re weighing the pros and cons of your food choices for the environment, not to mention for your waistline, keep in mind that food guidelines change over time, one decade warning against the dangers of coffee, alcohol and fat, the next suggesting that a balanced diet including all of the above may, in fact, be better for your individual health than abstaining.

Whether that diet is good for the planet is another question entirely.