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Probing the healthiest of all vegetables


You may have already seen the headline (or a variant) somewhere. Here’s Yahoo’s.

According to a study from the U.S. Centers for Disease Control (CDC), the winner of “the healthiest vegetable” is watercress, which by the criteria of the study cited, scores 100 percent, making it the top “powerhouse” vegetable.

Some caveats are in order. News sources have picked up this story from healthy-eating magazine Prevention.

Headshot of Richard Smoley

Prevention says, “Agriculture and nutrition experts have recently identified the healthiest vegetable on Earth” (my emphasis). This depends on your definition of “recently.”

The study cited is actually from 2014.

Of course, that doesn’t make the story invalid: nutrient properties do not change radically over 9 years. But that does make it less newsy.

The study ranked produce items on the basis of whether they provide, “on average, 10% or more daily value per 100 kcal of 17 qualifying nutrients.”

It is puzzling, then, that the published paper only lists 10 nutrients: iron, riboflavin, niacin, folate, vitamin B6, vitamin B12, vitamin C, and vitamin K.

After watercress come Chinese cabbage (91.99 percent), chard (89.27), beet greens (87.08 percent), and spinach (86.43). Parsley is high, at 65.59 percent (did you eat that sprig on your plate?).

In sum, “items in cruciferous (watercress, Chinese cabbage, collard green, kale, arugula) and green leafy (chard, beet green, spinach, chicory, leaf lettuce) groups were concentrated in the top half of the distribution of scores . . . whereas items belonging to yellow/orange (carrot, tomato, winter squash, sweet potato), allium (scallion, leek), citrus (lemon, orange, lime, grapefruit), and berry (strawberry, blackberry) groups were concentrated in the bottom half.”

By these standards, beet greens are much healthier than strawberries (17.59 percent) or the sweet potato, at a pathetic 10.51 percent. Even lower was the unfortunate white grapefruit, which sat at the bottom of the list with 10.47 percent.

“Of 47 foods studied, all but 6 (raspberry, tangerine, cranberry, garlic, onion, and blueberry) satisfied the powerhouse criterion,” we also learn.

The paper cites another study, which describes “apples, bananas, corn, and potatoes” as “low-nutrient-dense.”

Let us now turn to the implications, as described in the study:

“The focus on individual foods in terms of the nutrients they provide may facilitate better understanding of PFV [powerhouse fruits and vegetables] than green leafy, yellow/orange, citrus, and cruciferous food groups that are emphasized. Messages might specify PFV to help consumers know what they are and choose them as part of their overall fruit and vegetable intake. As numeric descriptors of the amount of beneficial nutrients PFV contain relative to the energy they provide, the scores can serve as a platform for educating people on the concept of nutrient density. Expressing the nutrient desirability of foods in terms of the energy they provide may help focus consumers on their daily energy needs and getting the most nutrients from their foods. The rankings provide clarity on the nutrient quality of the different foods and may aid in the selection of more nutrient-dense items within the powerhouse group.”

Subtleties aside, this ranking is unlikely to “facilitate better understanding” of nutrients among consumers. I come away from the paper with the impression that apples, bananas, corn, and potatoes have low nutrient value.

I also dislike the faddish implications of such findings. The Yahoo article begins, “Step aside, kale—there’s a new superfood on the scene.” Kale scores a mediocre 49.07 percent. Poor kale! Now a has-been.

Admittedly, there is probably some value in news items reminding us that green vegetables are packed with nutrients.

But the public has always known that vegetables are healthy (didn’t your mother tell you?). Translating that into increased consumption is another matter.


Richard Smoley, contributing editor for Blue Book Services, Inc., has more than 40 years of experience in magazine writing and editing, and is the former managing editor of California Farmer magazine. A graduate of Harvard and Oxford universities, he has published 13 books.