Take collard greens. They are 90 percent water, which still sounds like a lot. But it means that, compared with lettuce, every pound of collard greens contains about twice as much stuff that isn’t water, which, of course, is where the nutrition lives. But you’re also likely to eat much more of them, because you cook them. A large serving of lettuce feels like a bona fide vegetable, but when you saute it (not that I’m recommending that), you’ll see that two cups of romaine cooks down to a bite or two.
The corollary to the nutrition problem is the expense problem. The makings of a green salad — say, a head of lettuce, a cucumber and a bunch of radishes — cost about $3 at my supermarket. For that, I could buy more than two pounds of broccoli, sweet potatoes or just about any frozen vegetable going, any of which would make for a much more nutritious side dish to my roast chicken.
Lettuce is a vehicle to transport refrigerated water from farm to table. When we switch to vegetables that are twice as nutritious — like those collards or tomatoes or green beans — not only do we free up half the acres now growing lettuce, we cut back on the fossil fuels and other resources needed for transport and storage.
Save the planet, skip the salad.