Modern varieties of vegetables, the ones you see for sale in the produce section of the supermarket, are generally sweeter, starchier, and less fibrous than their wild ancestors. They are also far less nutritious: wild dandelion leaves, for example, have eight times more antioxidants than spinach and forty times more than iceberg lettuce.
So doing what you can to maximize the nutrients in the vegetables you eat is important — but it turns out that many common cooking habits are actually making vegetables less nutritious. Did you know you should wait 10 minutes before cooking chopped garlic? Or that broccoli is one of the most perishable vegetables in your crisper? Investigative journalist Jo Robinson spent 10 years combing through the latest research on nutrients in vegetables and fruits for her book, Eating on the Wild Side, and her evidence-based tips for storing and preparing vegetables will change the way you cook.
When you hear “nutrients,” you may only be thinking of vitamins, such as vitamins A and C, or minerals like calcium and iron. But vegetables are also a source of phytonutrients, the powerful antioxidants that plants produce in order to protect themselves from harmful UV light or damage from scavenging insects. “What [the scientific community] is discovering is that consuming these phytonutrients plays the same role for us, ” Robinson told me. “It protects us from external and internal threats.” Lycopene in tomatoes, resveratrol in red wine, and anthocyanins in blueberries are just a few of the phytonutrients scientists are excited about, and their names may be familiar to you.
Research on phytonutrients is relatively new, which is why tips about how to make the most of them in the kitchen are not yet common knowledge. Time to change that! Here are 10 ways you may be unknowingly making your vegetables less nutritious.
1. Buying fresh tomatoes instead of canned.
Cooking tomatoes makes them more nutritious, and the longer you cook them, the better. Heat changes the lycopene into a form our bodies can more readily absorb and — surprise! — canned tomatoes are much higher in phytonutrients, thanks to the heat of the canning process. Tomato paste, being more concentrated, is even better.
2. Storing lettuce wrong.
You might think that damaging your vegetables before storing them is a mistake, but when it comes to lettuce, tearing the leaves triggers a protective blast of phytonutrients that you can take advantage of by eating the greens within a day or two. Lettuce that is torn before storing can have double the antioxidants of whole lettuce leaves.
3. Boiling spinach — or any vegetable really.
You may have heard that boiling vegetables is a no-no because water-soluble vitamins like vitamin C leach out of the food and into the cooking water, but you might not know that boiling also reduces the antioxidant content. The difference in spinach is especially dramatic: after 10 minutes of boiling, three-quarters of its phytonutrient content is in cooking water, not in the vegetable itself. (Of course, if you consume the cooking liquid, as you do when making soup, you consume all the nutrients in the water as well.)
Steaming, microwaving, sautéing, and roasting — cooking methods that don’t put vegetables in direct contact with water — result in more nutritious vegetables on the plate.