The produce aisle now offers far more than plain iceberg lettuce. Shoppers can choose among romaine, red-leaf lettuce, butter lettuce, beet greens, bok choy, bitter radicchio and arugula at every stage of growth. For many, taste and texture decide the pick. But for those trying to hit a daily vegetable target of 2.5 cups, or for Americans rethinking their salad bowls in the wake of a cyclospora outbreak, the question of which greens are truly the most nutritious has become more urgent.
Nutrition experts point to “nutrient density” — the amount of nutrients per calorie — as a useful benchmark. Jamie Mok, a Los Angeles-based registered dietitian nutritionist, says this concept can guide produce choices. A 2014 study by the US Centers for Disease Control and Prevention ranked watercress at the top of its nutrient-density list, with 17 nutrients per calorie, nearly twice the density of kale. Mok, who grew up eating watercress in Chinese soups, notes that it is rich in vitamin K, vitamin C, minerals such as calcium and manganese, and a host of phytochemicals — beneficial plant compounds — all in a light, delicate leaf.
Yet experts caution against fixating on a single “best” green. Many other cruciferous vegetables, including green or Napa cabbage, kale and arugula, offer similarly substantial benefits. They contain glucosinolates, sulfur-containing compounds with antioxidant activity that researchers believe may help protect against cancer, along with vitamin C, vitamin K and fiber. “I don’t encourage people to focus on finding one ‘best’ leafy green,” says Dr Nina Cherie Franklin, a research scientist and health coach known as “That Salad Lady.” “Eating a variety is almost always the better approach.” Spinach, chard, collards, mustard greens, turnip greens and dandelion greens all bring something different to the bowl, she adds.
The nutritional differences are visible in the numbers. A cup of shredded cabbage provides about 2 grams of fiber and 28 milligrams of vitamin C but no vitamin A, while a cup of spinach delivers 1 gram of fiber, 9 milligrams of vitamin C and 16 micrograms of vitamin A. For convenience, pre-mixed mesclun — blends of mustard greens, arugula and lettuces — can be a practical way to get that variety, Mok suggests.
Does darker mean healthier? Generally, yes. The deep green of kale packs more nutrients, especially phytonutrients, than the pale leaves of iceberg lettuce. But lighter greens are far from empty, Franklin notes. Romaine, butter lettuce, endive and similar varieties still supply vitamins, fiber, hydration and beneficial plant compounds.
How greens are eaten also matters. Vitamins A, E and K are fat-soluble, so pairing greens with avocado, olive oil, eggs or other healthy fats improves absorption. Sauteing greens in olive oil can have the same effect, Mok says. Cooking also shrinks the leaves, making it easier to consume larger amounts: two cups of raw leafy vegetables count as just one cup of vegetables. For iron-rich greens such as spinach, Mok recommends adding vitamin C sources like citrus, bell peppers or tomatoes to enhance iron uptake.
Food safety is another consideration. Heating greens to about 160F (71C) can make them safer to eat, especially when there is concern about pathogens like cyclospora, E coli or salmonella. “Washing raw produce can reduce dirt and some contamination, but no home-washing method can guarantee the removal of every organism,” Franklin says, adding that cooking is more effective at lowering the risk of foodborne illness. For those who prefer raw salads, she advises washing hands and surfaces, discarding damaged leaves, rinsing greens thoroughly under running water and drying them with a clean cloth, paper towel or salad spinner.
Leafy greens are particularly vulnerable to contamination. Research from Ohio State University links leafy greens to up to 9 percent of pathogen-caused foodborne illnesses in the US, an estimated 2.3 million cases each year at a cost of more than $5 billion. Kristin Krokowski, a commercial horticulture educator at the University of Wisconsin-Madison, explains that the bumpy surfaces of leaves provide many tiny spots where organisms like cyclospora can attach, and the layered structure of head-forming greens can trap contaminants as well.