Recent trends in raw food diets ignore the fact that some vegetables are more nutritious when cooked. Cooking methods such as steaming or roasting can improve 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 some vitamins such as vitamin C, the overall absorption of nutrients is often increased, which benefits aspects such as immune function, bone growth and cancer prevention.
Cooked vegetables, including asparagus, mushrooms and spinach, often provide more nutrients than when raw, as cooking releases essential vitamins and antioxidants for enhanced health benefits.
Raw food diets are a relatively new trend, including raw food. The belief is that the less processed the food, the better. However, not every food is more nutritious when eaten raw. Indeed, some vegetables are actually more nutritious when cooked. Here are nine of them.
1. Asparagus
All living things are made of cells, and in vegetables, important nutrients are sometimes trapped in these cell walls. When vegetables are cooked, the walls break down, releasing the nutrients, which can then be more easily absorbed by the body. Cooking asparagus breaks down its cell walls, making vitamins A, B9, C and E more available for absorption.
When asparagus is cooked, its cell walls break down, releasing an abundance of nutrients that are otherwise hard to come by. This process makes vitamins A, B9 (folate), C and E more available for absorption. These vitamins play a critical 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, causing disease and aging.
3. Spinach
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 
Cooked tomatoes are a nutritional powerhouse, mainly due to the significant increase in lycopene, a powerful antioxidant, when heated. Lycopene has been linked to a reduced risk of chronic diseases, including heart disease and some cancers. While cooking tomatoes reduces their vitamin C content, the overall increase in bioavailable nutrients, especially lycopene, outweighs this loss.
4. Tomatoes
Cooking, using either method, greatly 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, which helps break down the thick cell walls that contain several important nutrients.
Although cooking tomatoes reduced their vitamin C content by 29%, their lycopene content increased by more than 50% within 30 minutes of cooking.
5. Carrots
Cooked carrots contain more beta-carotene than raw carrots, which is a substance called a carotenoid that the body converts to vitamin A. This fat-soluble vitamin supports bone growth, vision and the immune system.
Cooking carrots with their peels doubles their antioxidant power. You should boil carrots whole before slicing them, as this prevents these nutrients from leaching into the cooking water. Avoid frying carrots as this has been found to reduce the amount of carotenoid.
Peppers, when cooked, undergo a transformation that increases the availability of certain nutrients. Cooking breaks down their cell walls, making carotenoids like beta-carotene, beta-cryptoxanthin and lutein more absorbable. These antioxidants are vital for maintaining eye health and supporting the immune system.
6. Peppers
Peppers are a great source of immune-boosting antioxidants, especially the 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 boiled or steamed, as the vitamin can leach into the water. Try baking them instead.
7. Cabbage
Brassicas, which include broccoli, cauliflower and Brussels sprouts, are high in glucosinolates (sulphur-containing phytochemicals), which the body can convert into a number of cancer-fighting compounds. In order for these glucosinolates to be converted into cancer-fighting compounds, an enzyme in these vegetables called myrosinase must be active.
Research has found that steaming these vegetables preserves both vitamin C and myrosinase, and therefore the cancer-fighting compounds you can get from them. Cutting broccoli and letting it sit for a minimum of 40 minutes before cooking also allows this myrosinase to activate.
Likewise, sprouts, when cooked, produce indole, a compound that may reduce the risk of cancer. Cooking sprouts also causes glucosinolates to break down into compounds known to have anti-cancer 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 antioxidant levels in 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 levels of antioxidants when baked, microwaved, grilled, or even fried, as opposed to boiled or pressure-cooked.
9. Cale
Kale is healthiest when lightly steamed, as 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 larger amounts of water result in more nutrient loss. Water-soluble vitamins (C and many of the B vitamins) are the most unstable nutrients when it comes to cooking because they are leached from the vegetables into the cooking water. So avoid soaking them in water, use minimal amount of water when cooking and use other cooking methods like 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 on The Conversation.