‘In vegetables, important nutrients are sometimes trapped within the cell walls. When the vegetables are cooked, the walls break. ‘
Raw food diets are a fairly recent trend, including raw veganism, with the belief that the less processed the food, the better. However, not all food is more nutritious when eaten raw. In fact, some vegetables are actually more nutritious when cooked. Here are nine.
All living things are made up of cells and in vegetables sometimes important nutrients are trapped within these cell walls. When vegetables are cooked, the walls break, releasing nutrients that can then be absorbed more easily by the body. Cooking asparagus breaks down their cell walls, making vitamins A, B9, C and E more available to be absorbed.
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 packed with nutrients, including iron, magnesium, calcium, and zinc. However, these nutrients are more easily absorbed when spinach is cooked. This is because spinach is rich in oxalic acid (a compound found in many plants) which blocks the absorption of iron and calcium. Heating spinach releases the bound calcium, making it more available for absorption by the body.
Research suggests that steamed spinach maintains its folate (B9) levels, which may reduce the risk of some cancers.
Cooking, by any method, greatly increases the antioxidant lycopene in tomatoes. Lycopene has been 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 which helps break down the thick cell walls, which contain several important nutrients.
Although cooking the tomatoes reduces their vitamin C content by 29%, their lycopene content is increased 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 the peel doubles their antioxidant power. You should boil whole carrots before slicing them as it prevents these nutrients from escaping into the cooking water. Avoid frying carrots as this has been found to reduce the amount of carotenoids.
Peppers are an excellent source of antioxidants that stimulate the immune system, especially carotenoids, beta-carotene, beta-cryptoxanthin and lutein. Heat breaks down cell walls, making it easier for your body to absorb carotenoids. As with tomatoes, vitamin C is lost when peppers are boiled or steamed because the vitamin can leak into the water. Try roasting them instead.
Brassica, which includes broccoli, cauliflower, and Brussels sprouts, is rich in glucosinolates (phytochemicals containing sulfur), which the body can convert into a variety of anticancer compounds. In order for these glucosinolates to be converted into cancer-fighting compounds, an enzyme within these vegetables called myrosinase must be active.
Research has found that steaming these vegetables preserves both vitamin C and myrosinase and, therefore, the anticancer compounds you can get from them. Chopping the broccoli and letting it rest for a minimum of 40 minutes before cooking also allows this myrosinase to activate.
Likewise, the sprouts, once cooked, produce indole, a compound that can reduce the risk of cancer. Cooking the sprouts also causes the glucosinolates to break down into compounds known to have anticancer properties.
8. Green beans
Green beans have higher levels of antioxidants when baked, microwaved, broiled or even fried than boiled or pressure cooked.
Kale is healthier when lightly steamed as it deactivates enzymes that prevent the body from using the iodine it needs for the thyroid, which helps regulate metabolism.
For all vegetables, higher temperatures, longer cooking times and greater amounts of water result in the loss of more nutrients. Water-soluble vitamins (C and many of the B vitamins) are the most unstable nutrients when it comes to cooking because they seep from the 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 roasting. Also, if you have any cooking water left over, use it in soups or gravies as it contains all the leached nutrients. – The conversation | Rappler.com
Laura Brown is a senior professor of Nutrition, Food and Health Sciences at Teesside University.
This piece was originally published on The Conversation.