Vegetables are an excellent source of vitamins, minerals, phytochemicals, and fiber, and health-conscious consumers naturally want to know how to get the most nutritional impact from these powerful foods. “Nutritionally, there are pluses and minuses to cooking vegetables,” says Helen Rasmussen, PhD, RD, a senior research dietitian at Tufts’ Jean Mayer USDA Human Nutrition Research Center on Aging. For example, cooking carrots reduces levels of vitamin C (which plays an important role in maintaining collagen, the glue that holds cells together) but increases availability of beta-carotene, a precursor of vitamin A (which plays an important role in vision, reproduction, bone growth, and regulating the immune system).
Reduced Concentration. Some nutrients will be lost in any cooking method. “Some vitamins are not very stable,” says Rasmussen. “The longer a food is exposed to heat, the more vitamin C levels are reduced, for example.” The concentration of some nutrients is particularly affected by cooking in water. “Vitamin C and B vitamins are water soluble, as are certain phytochemicals, like flavonoids,” says Jeffrey B. Blumberg, PhD, a research professor at Tufts’ Friedman School of Nutrition Science and Policy. “They leach out into water when the vegetables are boiled.” Blumberg recommends eating produce high in these nutrients (like broccoli, kale, and bell peppers) raw. “When you do cook them, try methods like steaming, blanching, sauting, roasting, or microwaving, which use little water,” says Blumberg. If you do boil your vegetables in excess water, Rasmussen recommends using that water to make broths or sauces, rather than pouring nutrients down the drain.