Current raw food trends overlook the fact that some vegetables are more nutritious when cooked. Cooking methods such as steaming or roasting can increase the availability of essential nutrients in vegetables such as asparagus, mushrooms and spinach. This process releases important vitamins and antioxidants that are sometimes trapped in the vegetable’s cell walls. Although cooking can reduce certain vitamins such as vitamin C, overall nutrient intake is often increased, benefiting aspects such as immune function, bone growth and cancer prevention.
Cooked vegetables, including asparagus, mushrooms and spinach, often provide more nutrients than raw vegetables because cooking releases important vitamins and antioxidants that have positive effects on health.
Raw food diets are a relatively new trend, including raw veganism. It is believed that the less processed food there is, the better. However, not all foods are more nutrient dense when eaten raw. In fact, some vegetables are even more nutritious when cooked. Here are nine of them.
1. Asparagus
All living things are made of cells, and vegetables sometimes have important nutrients trapped within these cell walls. When vegetables are cooked, the walls break down and the nutrients are released, which are then more easily absorbed by the body. Cooking asparagus breaks down the cell walls, making vitamins A, B9, C and E easier to absorb.
When asparagus is cooked, its cell walls break down, releasing numerous nutrients that would otherwise be difficult to access. This process makes vitamins A, B9 (folate), C and E more available for absorption. These vitamins play a crucial role in maintaining immune health, skin health and cellular function.
2. Mushrooms
Mushrooms contain large amounts of the antioxidant ergothioneine, which is released when cooked. Antioxidants help break down “free radicals,” chemicals that can damage our cells and cause disease and aging.
3. Spinach
Spinach is rich in nutrients including iron, magnesium, calcium and zinc. However, these nutrients are more easily absorbed when the spinach is cooked. This is because spinach is full of oxalic acid 
Cooked tomatoes are a nutritional powerhouse, largely due to the significant increase in lycopene, a powerful antioxidant, when heated. Lycopene has been linked to a reduction in the risk of chronic diseases, including heart disease and certain types of cancer. While cooking tomatoes reduces their vitamin C content, the overall increase in bioavailable nutrients, particularly lycopene, outweighs this loss.
4. Tomatoes
Cooking, no matter the method, significantly increases the antioxidant lycopene content in tomatoes. Lycopene has been linked to a lower risk of a number of chronic diseases such as heart disease and cancer. This increased amount of lycopene comes from the heat helping to break down the thick cell walls that 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.
5. Carrots
Cooked carrots contain more beta-carotene than raw carrots, 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 on them more than doubles their antioxidant effects. You should cook the carrots whole before cutting as this will prevent these nutrients from leaching into the cooking water. Avoid frying carrots as this has been shown to reduce the amount of carotenoid.
When cooked, peppers undergo a transformation that increases the availability of certain nutrients. Cooking destroys their cell walls and makes carotenoids such as beta-carotene, beta-cryptoxanthin and lutein more absorbable. These antioxidants are crucial for maintaining eye health and supporting the immune system.
6. Paprika
Bell peppers are a great source of immune-boosting antioxidants, particularly the carotenoids, beta-carotene, beta-cryptoxanthin and lutein. Heat destroys the cell walls, making the carotenoids easier to absorb into the body. As with tomatoes, vitamin C is lost when peppers are cooked or steamed because the vitamin can leach into the water. Try roasting them instead.
7. Cabbage
Cabbage, which includes broccoli, cauliflower and Brussels sprouts, is rich in glucosinolates (sulfur-containing phytochemicals) that 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 called myrosinase must be active in this vegetable.
Research shows that steaming these vegetables preserves both vitamin C and myrosinase, and therefore the cancer-fighting compounds you can get from them. Chopping broccoli and letting it rest for at least 40 minutes before cooking also activates this myrosinase.
Likewise, when cooked, sprouts produce indole, a compound that may reduce the risk of cancer. Cooking sprouts also causes the glucosinolates to break down into compounds known to have cancer-fighting properties.
Cooking green beans can increase their nutritional value, especially in terms of antioxidant content. Various cooking methods such as baking, microwaving, and grilling have been shown to increase the antioxidant content of green beans compared to boiling or pressure cooking. These antioxidants play a crucial role in protecting the body from oxidative stress and inflammation.
8. Green beans
Green beans have higher antioxidant content when baked, microwaved, grilled, or even fried, as opposed to boiled or pressure cooked beans.
9. Kale
Kale is healthiest when lightly steamed because it deactivates enzymes that prevent the body from using needed iodine for the thyroid, which helps regulate metabolism.
For all vegetables, higher temperatures, longer cooking times and larger amounts of water lead to more nutrients being lost. Water-soluble vitamins (C and many of the B vitamins) are the most unstable nutrients in cooking because they leach from vegetables into the cooking water. Therefore, avoid soaking them in water, use the least amount of water when cooking, and use other cooking methods such as steaming or frying. Additionally, if you have leftover cooking water, use it in soups or sauces as it contains all the nutrients that have been leached out.
Written by Laura Brown, Lecturer in Nutrition, Food and Health Sciences, Teesside University.
Adapted from an article originally published in The Conversation.