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. 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. 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. They leach out into water when the vegetables are boiled. Try 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. If you do boil your vegetables in excess water, use that water to make broths or sauces, rather than pouring nutrients down the drain.
Increased availability
Eating a raw diet to avoid losing nutrients to cooking is not the answer. A study published back in 2008 found that following a strict long-term raw food diet was associated with relatively high blood levels of beta-carotene and normal levels of vitamin A, but low levels of prostate-cancer fighting lycopene. Heat breaks down the cell matrix and allows some nutrients to be released from the cell walls. This explains why studies find cooked tomato products like tomato sauce and ketchup have higher levels of available lycopene than raw tomatoes. Other studies have found vegetables like carrots, spinach, broccoli, mushrooms, zucchini, asparagus, cabbage, and peppers supply more carotenoids to the body when cooked than when eaten raw.
Method matters
How vegetables are cooked and eaten does make a difference in nutrient availability and absorption. In general, steaming preserves nutrients best, since this method avoids the leaching of water-soluble compounds and limits exposure to heat that can degrade some vitamins. Regardless of cooking method, some nutrients will be better absorbed if veggies are prepared or eaten with some healthy fat. Fat soluble vitamins (A, D, E, and K) and phytonutrients (especially beta-carotene, lycopene, and other carotenoids) are better absorbed when cooked with vegetable oil. Chopping also helps release these health-promoting compounds.
When eating vegetables raw, such as in a salad, add some dressing, avocado, or nuts to help with absorption of fat-soluble nutrients. The best choice is to eat vegetables however they most appeal to you. Taste and texture matter. If you don't like them, you won't eat them at all. More important than raw versus cooked is to eat your veggies. Getting 50 percent of a nutrient is still better than getting nothing.
Take charge of your health
Eat a variety of vegetables and enjoy them raw or cooked to vary the nutrients your body receives.
Cook with less water and heat exposure when possible to preserve water-soluble and heat-sensitive nutrients. (Try steaming, microwaving, or blanching.)
Pair veggies high in fat-soluble nutrients (such as asparagus, carrots, Swiss chard, and squash) with healthy fats (like vegetable oil, seeds, nuts, and avocado) to increase absorption.
Store non-root veggies in the refrigerator to preserve nutrients longer (although keeping some out where they can be seen may increase intake).
Wash raw vegetables well to remove any bacteria. Rinse with clean cold water; use a vegetable brush for produce with thick skin; soak produce with nooks and crannies (such as broccoli and cauliflower) for one to two minutes in clean cold water.
Adapted from: Medical Xpress
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