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Does cooking vegetables change their nutritional value?

By The Health News Team | July 1, 2020
Vegetables cooking in a wok on the stove

When it comes to your health, vegetables have superpowers. They help boost your immune system, reduce inflammation and protect against diseases.
A bonus? In addition to eating them raw, vegetables can be roasted, boiled, steamed and fried, creating endless cooking and serving opportunities to make the most out of your farmers market bounty.
One question remains: Does cooking vegetables rob you of essential vitamins and minerals? According to Lauren DeWolf, MS, RD, a wellness education specialist with Sharp Rees-Stealy’s Center for Health Management, the answer is both yes and no.
“The way you prepare vegetables can alter their nutritional quality,” DeWolf says. “How they are altered depends on the vitamin or mineral. While some vitamins can be degraded, some can actually be improved by heating them.”
Water-soluble vitamins, such as B and C, are the most sensitive to cooking methods. These vitamins have a tendency to leach out of veggies when boiled — and can be degraded by heat. Yet fat-soluble vitamins, such as A, D, E and K, fare better during the cooking process. When it comes to minerals, heat can improve the ability of some to be digested, absorbed and metabolized.
5 ways to prep your produce
DeWolf shares the five most common cooking (and non-cooking) methods, and how they impact the nutritional integrity of veggies:

  1. Raw — While you won’t lose any nutrients by eating them raw, some veggies, such as squash or potatoes, are difficult to eat and digest without cooking them.

  2. Roasted or broiled — Dry heat cooking methods are a great way to enjoy vegetables without losing too many nutrients. Plus, roasting or broiling make tougher vegetables more palatable and easier to digest.

  3. Boiled — When cooking vegetables over a long period of time in water, some nutrients will be lost. However, if the water will be consumed with the vegetables — as in the case of soups, stews or curries — many of the vitamins will be retained in the final dish.

  4. Steamed — Because vegetables do not come in contact with cooking water during the steaming process, most vitamins are retained, and tougher vegetables can be more easily digested.

  5. Stir-fried or sautéed — Stir-frying your veggies — with a small amount of heart-healthy oil — can help enable your body to absorb fat-soluble vitamins. You can replace the oil with vegetable broth, if cooking your veggies with food that contains its own fat. 

Frozen or canned?
Frozen vegetables can closely match the nutrient content of their fresh counterparts. Some vegetables are flash-frozen shortly after harvest, a time when their nutritional content is highest.
In general, vitamins and minerals are unchanged by the canning process. However, canned veggies may have fewer water-soluble vitamins, such as B and C. Always look for low-sodium canned veggies, and rinse well before using.
Variety is key
Knowing that vitamins and minerals behave differently depending on how vegetables are prepared, it’s important to add variety to how your vegetables are consumed.
“When choosing between raw and cooked veggies, remember that they each have their advantages and disadvantages,” DeWolf says. “Your goal should be to diversify your portfolio, ensuring you maximize a vegetable’s best qualities.”
It’s also important to diversify the kind of vegetables you eat. Consuming veggies in a variety of colors helps your body get a range of phytonutrients — compounds found in plants that support health and help prevent against disease.
DeWolf offers the following creative suggestions for diversifying the produce in your diet:
Skewer ’em up. Veggie kebabs are a colorful and flavorful way to enjoy a mix of nutrient powerhouses. Try packing a skewer with bell peppers, mushrooms, zucchini, yellow squash and red onion, and tossing them on the grill.
Break out the blender. Adding veggies to your morning smoothie is an easy way to take advantage of their raw power. Frozen spinach and kale blend nicely with frozen fruit and almond or low-fat milk. And for a sweet treat, try a carrot cake smoothie — a mix of raw carrots, frozen pineapple, Greek yogurt, oats, nut butter and your favorite milk.
Get sneaky. If your favorite foods are lacking in the nutrition department, find ways to add a veggie or two. For example, blend beets into your hummus, puree butternut squash or cauliflower into your mac ’n’ cheese, or use spiralized or thinly sliced zucchini “noodles” instead of pasta.
Focus on comfort. Soup, the ultimate comfort food, allows vegetables to take center stage. Vegetable soup is a great way to clear your fridge of about-to-expire produce, while adding a mix of vitamins and nutrients in one nourishing meal.
Boost the flavor. Spices bring out the best in veggies, and finding your perfect combination creates a taste profile personal to you.
“There are so many great ways to prepare produce,” DeWolf says. “And while cooking methods do have an impact on keeping or enhancing vitamins and minerals, the main goal is to ensure that we’re eating them in the first place.”

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