Spinach is loaded with vitamins A, C, E, and K, carotenoids, folic acid, potassium, magnesium, and iron--in short, it's a nutrient-dense food containing many of the phytochemicals that help prevent chronic disease. But like its relatives chard and beet greens, spinach is very high in oxalic acid, which leeches calcium and iron from the body.
Verdict: Consume spinach in moderation--eating a spinach salad every day is not the best idea. While cooking spinach with fat-containing foods like cheese, seeds, eggs, or oil will help counteract the effects of the oxalic acid, it's best to alternate between spinach and some low-oxalate greens, like kale and collards.
While many types of lettuce are full of vitamins and minerals, the most commonly consumed lettuce in the U.S. is iceberg, which offers little more than water and a small amount of fiber. For comparison, romaine lettuce, the staple of Caesar salads, contains six times more Vitamin C.
Verdict: Eat the darker lettuce varieties. And watch what kind of dressing you put on your salad--creamy dressings are often loaded with fat, sugar, and additives, and will turn your healthy salad into something with the caloric profile of a fast-food meal.
Cabbage is one of the world's most widely grown vegetables. A member of the cruciferous vegetable family, cabbage contains sulforaphane, which helps guard against the development of cancerous tumors. And when fermented to make sauerkraut, cabbage does everything from helping to foster clear skin to promoting the growth of healthy flora in the digestive tract.
Verdict: An underappreciated nutritional powerhouse. And sauerkraut is truly a health food if bought fresh and unpasteurized (pasteurization kills the beneficial bacterial cultures) or made from scratch.
Edible wild greens--including such common weeds as dandelion, lamb's quarters, chickweed, and amaranth--are often more nutritious than the cultivated greens available in your supermarket. If you take a class or go on a nature walk with a knowledgeable guide who can help you ID these plants, you've got yourself a way to add some exotic flavors, for free, into your diet.
Verdict: Put away that weed-whacker! If you're up for a little experimentation, wild greens are worth checking out.