“In vegetables, important nutrients can be trapped in the cell wall. When vegetables are cooked, the wall collapses.”
Raw food diets are a fairly recent trend, including raw vegetarianism, and there is a belief that less processed foods are better. However, not all foods are more nutritious when eaten raw. Indeed, some vegetables are more nutritious when actually cooked. Here are nine of them.
1. Asparagus
All organisms are made up of cells, and in vegetables important nutrients can be trapped in these cell walls. When vegetables are cooked, the walls collapse and nutrients are released, making them easier for the body to absorb. Cooking asparagus destroys the cell walls and facilitates the absorption of vitamins A, B9, C and E.
2. Mushroom
Mushrooms contain large amounts of the antioxidant ergothioneine, which is released during cooking. Antioxidants help break down “free radicals,” chemicals that can damage cells and cause illness and aging.
3. Spinach
Spinach is rich in nutrients such as iron, magnesium, calcium and zinc. However, when you cook spinach, these nutrients are more easily absorbed. This is because spinach contains oxalic acid (a compound found in many plants) that interferes with the absorption of iron and calcium. Heating spinach releases bound calcium, which makes it easier for the body to absorb.
Studies show that steaming spinach may maintain folic acid (B9) levels and reduce the risk of certain cancers.
4. Tomato
Cooking using any method will significantly increase the antioxidant lycopene in tomatoes. Lycopene is associated with a low risk of various chronic illnesses, including heart disease and cancer. This increased amount of lycopene comes from the heat that helps destroy the thick cell walls that contain some important nutrients.
Cooking tomatoes reduced the vitamin C content by 29%, while the lycopene content increased by more than 50% within 30 minutes of cooking.
5. Carrot
Cooked carrots contain more beta-carotene than raw carrots, a substance called carotenoids that the body converts to vitamin A. This fat-soluble vitamin supports bone growth, vision and the immune system.
Cooking carrots with skin more than doubles their antioxidant power. Whole carrots need to be boiled before slicing as these nutrients prevent them from escaping into the cooking water. Avoid frying carrots as they are known to reduce the amount of carotenoids.
6. Bell pepper
Bell peppers are an excellent source of antioxidants that boost the immune system, especially carotenoids, beta-carotene, beta-cryptoxanthin, and lutein. Heat destroys the cell walls and makes it easier for the body to absorb carotenoids. Like tomatoes, boiling and steaming peppers loses vitamin C. This is because vitamins can seep into the water. Try roasting them instead.
7. Brassica
Brassica, including broccoli, cauliflower and Brussels sprouts, is high in glucosinolates (sulfur-containing phytochemicals) that the body can convert into compounds that fight a variety of cancers. In order for these glucosinolates to be converted into cancer-fighting compounds, an enzyme in these vegetables called myrosinase must be active.
Studies show that steaming these vegetables preserves both vitamin C and myrosinase, thus preserving the cancer-fighting compounds that result from them. This myrosinase is activated by chopping broccoli and leaving it for at least 40 minutes before cooking.
Similarly, bean sprouts, when cooked, produce indole, a compound that has the potential to reduce the risk of cancer. When Brussels sprouts are cooked, glucosinolates are broken down into compounds known to have cancer-fighting properties.
8. Green beans
Green beans have higher levels of antioxidants when baked, microwaved, gridded, or fried, as opposed to boiling or cooking in a pressure cooker.
9. Kale
Kale is the healthiest because light steaming helps to regulate metabolism by inactivating enzymes that prevent the body from using the iodine it needs for the thyroid gland.
For all vegetables, the higher the temperature, the longer the cooking time, and the higher the water content, the more nutrients will be lost. Water-soluble vitamins (C and many B vitamins) are the most unstable nutrients for cooking because they leach from vegetables into the cooking water. Therefore, avoid soaking in water, use minimal water when cooking, and use other cooking methods such as steaming and roasting. Also, if cooking water remains, it retains all the leached nutrients and should be used in soups and gravy sauces. – The Conversation | Rappler.com
Laura Brown is a senior lecturer in nutrition, food and health sciences at Teesside University.
This work was originally published in The Conversation.
