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We should eat more plants. Here’s which ones are best for the planet.

(Washington Post Illustration)

So you’re thinking about eating more plants?

You’re in good company. Whether people are actually doing it, they’re certainly thinking and talking about it. A recent poll from Oklahoma State University that’s still undergoing peer review puts the number of American adults who say they’re vegan or vegetarian at 10 percent (a number consistent with other polls I’ve seen). Meanwhile, flexitarianism has also become a thing, and plant messages are everywhere.

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Plants themselves, not so much. So far, there’s no evidence that people are actually eating more of them — and meat consumption hasn’t decreased — but if you’re gonna do something, talking and thinking about it is a necessary first step.

Eating more plants gives you lots of room to maneuver because there are lots of kinds of plants. But, from a climate perspective, they’re not created equal; some are way better than others. If climate impact is one of the things making plants climb your personal dinner chart, it helps to know which tread most lightly on our earth.

Vegetables

When you think of vegans and vegetarians, you naturally think of vegetables. Salads, leafy greens, broccoli, asparagus! And they’re all better climate choices than meat. But, among plants, they’re the worst choice. Sounds weird, I know, because they’ve gotten more of a health halo than any other plant category, but there are three reasons vegetables are climatically suboptimal.

The first is that they have higher fertilizer and pesticide loads than most other plant crops. While there aren’t reliable input-per-crop statistics (that I’ve found), you can get a sense of the disparity by looking at production costs. A 2017 analysis of broccoli’s costs puts fertilizer at $269 and pesticides at $335, about $600 per acre per year. Look at corn or soy from that same year, and total fertilizer and pesticide costs ran about $200 per acre for corn, and less than $100 for soybeans. Vegetables are also mostly irrigated, and mostly tilled (California, for example, has very few no-till acres). Consequently, their impact on the environment is relatively heavy.

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Second is their perishability, which contributes to food waste. Something like one-third of the food we grow in the United States gets wasted, but for fruits and vegetables, it’s closer to half. I’m betting that, if you were to check your fridge right now, you’d find something at the bottom of the crisper to prove the point.

Third is that most vegetables, especially the green kind, have very few calories, and that’s a conundrum. In a world of overabundance, where obesity is a pressing public health problem, foods with few calories are a good thing. But when we have a growing population to feed, and limited land on which to do it, using that land to grow nutrients without calories is a luxury.

We’ve got about 7.7 billion people on Earth, and 2.7 billion acres growing crops. That comes to one-third of an acre per person, to grow crops both for us and the animals we eat (we also get calories from grazing animals, which is problematic for other reasons). Green vegetables yield some of the lowest calories per acre; spinach and leaf lettuce, for example, are about 1.6 million. Yes, they’re high in nutrition! But ideally, we’re looking for crops that deliver both calories and nutrition. Oh, and protein’s good, too; there are still places in the world where people don’t get enough (although the United States is emphatically not one of them).

I’m not anti-veg! I eat plenty of them, and they absolutely, positively have a place in a diet that both people and planet can thrive on. But if you eat more than a few servings a day, your diet’s going to have a bigger climate impact than if you focus on other kinds of plants.

Fruits and nuts

Climate-friendly foods grow on trees!

Tree fruits and nuts aren’t perfect. Fruits use a lot of pesticides (one 2019 estimate for growing apples in Washington state puts the cost at nearly $2,000 per acre per year), and nuts use a lot of water (almost 500 gallons per pound), but the amount of food they produce — without farmers having to till soil and replant every year — makes them some of the most climate-friendly foods we can eat. Apples, oranges and avocados (yes, a fruit) come in at 5 million to 7 million calories per acre, and nuts do even better, with almonds and walnuts in the 6-million-to-7-million range.

Plant an orchard, and you get a climate twofer: food, but also the perennial, carbon-storing plants they grow on.

On a per-calorie basis, apples have less than one-third the climate impact of brassicas (the group of vegetables that includes cauliflower, broccoli and cabbage). While berries and grapes aren’t quite as good as tree fruits, with almost three times the impact of apples, they’re still a fine choice. Nuts are crazy carbon-friendly, with a mere 2 percent of the footprint of that cauliflower rice.

Row crops

These are the crops that, obviously, grow in rows, but are also planted and harvested by big machines. It’s corn and soy, but also oats, barley, wheat, dry beans, chickpeas, lentils and all the other grains and legumes that are the backbone of a diet that’s good for both people and planet.

Let’s start with corn and soy, which are, respectively, the highest-yielding cereal grass and plant protein source we grow. Corn rolls in at about 15 million calories per acre, and soy is about 6 million (protein production uses a lot of plant resources, so high-protein crops are generally lower-yielding).

I know what you’re thinking: “But externalities!”

And there are many! I think the biggest one is that nutrient runoff causes toxic algae blooms and fish kills. But all crops use fertilizer (and the nutrients can be from either manure or chemical versions), and vegetables use more than the crops we’ve all learned to hate.

The externality that’s unique to corn and soy is the obesity and disease that result from eating way too many foods that contain the industrial ingredients derived from them. But imagine if, instead of putting our crops into cars (about 40 percent of our corn becomes ethanol) and pigs (another 40 percent of corn and 70 percent of soy become animal feed) and Twinkies (most of the rest goes into processed foods), we ate them as tortillas and tofu? Our 90 million acres of corn and 88 million acres of soy could, together, meet the caloric needs of nearly a quarter of the entire world’s population. (No, of course, people shouldn’t eat exclusively corn and soy. I’m just trying to give this a sense of scale.)

Staple crops — whole grains and legumes, but also tubers (potatoes and sweet potatoes) and even some starchy tree fruits (jackfruit and bananas) — are where the climate action is. They’re healthful, nutritious, versatile and much less perishable than garden-variety fruits and veg. They deliver calories and nutrition in one package. They use fewer inputs than other plants, and they’re often grown without irrigation.

I’d go so far as to suggest that we need a name for a diet that’s mostly staple crops, but “stapletarian” sounds like you’ve got a job in the copy shop. If you’ve got a better idea, please let me know.

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