Environment
Here’s a look at why greens are so vulnerable to contamination, how to avoid getting sick, and whether you can really trust labels that say “triple-washed.”
BySarah Gibbens
Published October 19, 2023
• 8 min read
After a long night of whatever long nights mean to you, there’s nothing quite as redeeming as a bowl of leafy greens.
Kale, spinach, mesclun, romaine, buttery-soft baby bibb—leafy greens tossed with veggies and proteins are the gastronomical equivalent of sleeping on fresh sheets.
When I eat a big bowl of greens, I just feel healthy—knowing that their vitamins, fiber, and other nutrients have been dispatched to perform cellular maintenance. But is there actually something more sinister nestled among all that microscopic goodness?
Leafy greens, infamously, are regularly recalled for contamination. They’re the vegetables most likely to get you sick according to a 20-year study of California’s contaminated produce. One of the most famous outbreaks occurred in 2006 when spinach contaminated with the bacteria E. Coli hospitalized 200 people and caused 18 deaths. Just this past June, a listeria outbreak in leafy greens hospitalized 18 people.
These cases make me pause when I reach for my weekly bag of kale, and I’m not alone. One Consumer Reports survey of a thousand shoppers found half had the same concerns.
How do we weigh these risks—and is the risk of getting sick even that high at all? Here’s a breakdown of which lettuces are healthiest, exactly why they can be so vulnerable to contamination, and why pre-washed bags of greens may not be as safe as you think.
And if you have more questions about navigating the science of your everyday life, tag me on X (formerly known as Twitter), or send me an email here.
Which greens are the healthiest?
Our bodies need different nutrients and vitamins to properly function. By eating just a cup of kale, an average adult woman like me could get half her recommended intake of vitamin A, nearly a third of her daily recommended intake of vitamin C, and nearly all her recommended vitamin K (a vitamin that helps build healthy bone tissue).
And while I’d still need a well-rounded diet to get my needed daily dose of dietary fibers, protein and minerals like potassium and magnesium, that cup of kale could help me get part of the way there.
(Learn more about how magnesium affects your sleep and anxiety.)
“[Leafy greens] quite literally are these powerhouses of nutrients,” says Debbie Fetter, a nutritionist at the University of California, Davis.
What exactly are leafy greens, you asked? This large category of vegetables describes the literal vegetable leaves we eat: lettuce, which encompasses romaine and iceberg, as well as other greens like kale, arugula, and spinach. All these greens are healthy, but they vary in the amount of vitamins and minerals they imbue. A single cup of romaine lettuce would trump that cup of kale when it comes to vitamin A, but it’s much lower in vitamins C and K.
Using data from the U.S. Department of Agriculture, the Harvard Medical School created this helpful chart showing which greens provide which benefits.
Personally, I love finely chopped and oil-massaged curly kale, which means I’m in luck—a good rule of thumb for choosing the most nutritious greens is to select the darkest green colors, according to the Academy of Nutrition and Dietetics.
But Fetter says that guiding principle isn’t a perfect science and consuming a variety of greens means you’ll also be consuming a variety of different benefits.
Ultimately, the best greens for you are probably the ones you’ll eat the most often.
“I always recommend people pick the ones they like because life is too short to force yourself to eat something just because you hear it’s healthy,” she says. “There are so many options out there that you’re bound to find one that fits your taste.”
Are leafy greens dangerous to eat?
Despite their myriad benefits, the fact that lettuce could make me sick is enough to keep me vigilant. Because while rare, the risk is still very real.
From 2014 to 2020, the U.S. Centers for Disease Control and Prevention logged over 2,000 illnesses and 18 deaths from leafy greens. And in the two decades spanning 1996 to 2016, leafy greens dominated the list of vegetables likely to be the source of food-related illnesses, according to the California Department of Public Health.
Lettuce made up nearly 40 percent of those incidents and spinach was a close second, making up 26 percent of those incidents.
“If you look at the way romaine lettuce grows, it creates a funnel. The leaves are uneven and corrugated. Some of these bacteria can attach and stick to the leaves,” says Michele Jay-Russell, a microbiologist at the University of California, Davis, who studies leafy green food safety.
She says her personal favorite, spinach, “has some unique risks because it’s grown so close to the ground.”
While that recent California study showed other greens like radicchio, chard, kale, and cabbage only had outbreaks in the single digits, they still beat out all the rest of the vegetables studied.
Nailing down exactly where the bacteria that contaminates these greens is coming from is complex.
“We don’t have fields where cattle are just pooping in the field. It’s much more subtle. And there’s very little indication that it’s coming from farm workers,” says Jay-Russell.
Anything from birds swooping down and defecating in an irrigation canal to floodwaters washing dirty water onto a field could cause an outbreak.
But another reason leafy greens are so frequently caught up in recalls might simply be that we eat them raw instead of cooking them like we do with other vegetables.
That deprives the greens of what Jay-Russell calls a “kill step,” a surefire way to completely eliminate any viruses or bacteria—the same way that pasteurizing milk makes it safer to drink milk.
Leafy greens might also be overrepresented in causing food-borne illnesses because of their popularity, Jay-Russell says—meaning more people buy them and are potentially exposed to their risks than other produce. According to the International Fresh Produce Association, lettuce was the fourth most popular veggie purchased in 2022, and other leafy greens followed close behind.
So what can you do to avoid food-borne illnesses
The most obvious precaution to take with greens is to throw out any greens in your kitchen that have been recalled for known contamination.
And if you’re tempted to seek out those plastic containers of triple-washed lettuce the next time you’re at the grocery store, you might want to think again. Pre- and triple-washed labels aren’t regulated by the U.S. Food and Drug Administration, and even these products have been recalled for contamination risks.
“It makes a difference, but it’s not a guarantee,” says Jay-Russell.
(And who wants to buy all that plastic anyway?)
But, she says, if you do buy pre-washed, ready-to-eat, or triple-washed greens, you might as well eat them as-is instead of additionally washing it in your sink because the average kitchen sink is known to be a hotbed of germs. (I wrote more about that back in 2018.)
If you got your greens fresh at the market—in which case, kudos to you—you do need to give them a rinse. The CDC recommends rinsing them off in water. Not diluted bleach. Not a vinegar solution. Just water.
With just a little vigilance, we can have our greens and eat them too.
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