Cooked vegetables, including asparagus, mushrooms and spinach, often provide more nutrients than raw, as cooking releases essential health-boosting vitamins and antioxidants.
Raw food diets are a fairly recent trend, including raw veganism. It is believed that the less processed food, the better. However, not all foods are more nutritious when eaten raw. Indeed, some vegetables are actually more nutritious when cooked. Here are nine of them.
All living things are made up of cells, and in vegetables, important nutrients are sometimes trapped within these cell walls. When vegetables are cooked, the walls break down, releasing nutrients that are more easily absorbed by the body. Cooking asparagus breaks down its cell walls, making vitamins A, B9, C and E more available for absorption.
Mushrooms contain large amounts of the antioxidant ergothioneine, which is released during cooking. Antioxidants help break down free radicals, chemicals that can damage our cells, causing disease and aging.
Spinach is rich in nutrients, including iron, magnesium, calcium and zinc. However, these nutrients are more easily absorbed when spinach is cooked. This is because spinach is full of oxalic acid acid (a compound found in many plants) that blocks the absorption of iron and calcium. Heating the spinach releases the bound calcium, making it more available to the body for absorption.
Research suggests that steamed spinach maintains folate (B9) levels, which may reduce the risk of certain cancers.
Cooking, using any method, significantly increases the antioxidant lycopene in tomatoes. Lycopene is associated with a lower risk of a number of chronic diseases, including heart disease and cancer. This increased amount of lycopene comes from the heat that helps break down the thick cell walls, which contain several important nutrients.
Although cooking tomatoes reduces their vitamin C content by 29%, their lycopene content increases by more than 50% within 30 minutes of cooking.
Cooked carrots contain more beta-carotene than raw carrots, which is a substance called a carotenoid that the body converts into vitamin A. This fat-soluble vitamin supports bone growth, vision and the immune system.
Cooking carrots with their peels more than doubles their antioxidant power. You should boil the carrots whole before cutting as this prevents these nutrients from escaping into the cooking water. Avoid frying carrots as this has been found to reduce the amount of carotenoids.
Paprika is an excellent source of antioxidants that strengthen the immune system, especially carotenoids, beta-carotene, beta-cryptoxanthin and lutein. The heat breaks down the cell walls, making the carotenoids easier for your body to absorb. As with tomatoes, vitamin C is lost when peppers are cooked or steamed because the vitamin can leach into the water. Try baking them instead.
Brassica, which includes broccoli, cauliflower and Brussels sprouts, is high in glucosinolates (sulfur-containing phytochemicals), which the body can convert into a range of cancer-fighting compounds. In order for these glucosinolates to be converted into cancer-fighting compounds, an enzyme in this vegetable called myrosinase must be active.
Research has found that steaming these vegetables preserves both vitamin C and myrosinase, and thus the cancer-fighting compounds you can get from them. Chopping the broccoli and letting it sit for at least 40 minutes before cooking also allows the myrosinase to activate.
Similarly, sprouts, when cooked, produce indole, a compound that may reduce the risk of cancer. Cooking the sprouts also causes glucosinolates to break down into compounds known to have cancer-fighting properties.
Green beans have higher levels of antioxidants when baked, microwaved, grilled, or even fried, as opposed to boiled or pressure-cooked.
Kale is healthiest when lightly steamed because it deactivates enzymes that prevent the body from using the iodine it needs for the thyroid gland, which helps regulate your metabolism.
For all vegetables, higher temperatures, longer cooking times and higher amounts of water lead to more nutrient loss. Water-soluble vitamins (C and many B vitamins) are the most unstable nutrients when it comes to cooking, as they leach out of vegetables into the cooking water. So avoid soaking them in water, use the least amount of water when cooking and use other cooking methods, such as steaming or baking. Also, if you have leftover cooking water, use it in soups or sauces as it contains all the leached nutrients.
Written by Laura Brown, Senior Lecturer in Nutrition, Food and Health Sciences, Teesside University.
Adapted from an article originally published in The Conversation.
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