Raw foods and accompanying diets are a fairly recent trend, including raw veganism.

The belief is that the less processed food, the better. However, not all foods are more nutritious when eaten raw. Indeed, some vegetables are more nutritious when cooked. Here are nine.

1. Asparagus

All living things are made up of cells; in vegetables, important nutrients are sometimes locked up in these cell walls. When vegetables are cooked, the barriers break down, releasing nutrients that are easier for the body to absorb. When asparagus is cooked, the cell walls are broken down, making vitamins A, B9, C, and E more available for absorption.

2. Mushrooms

Mushrooms contain high amounts of the antioxidant ergothioneine released during cooking. 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 (a compound found in many plants) that blocks the absorption of iron and calcium. Heating spinach releases bound calcium, making it more available for the body to absorb.

Research suggests that steaming spinach maintains its folate (B9) content, possibly reducing the risk of certain cancers.

4. Tomatoes

Cooking, either way, significantly increases the antioxidant lycopene in tomatoes. This increased amount of lycopene comes from the heat that helps break down the thick cell walls, which contain several important nutrients. Lycopene has been linked to a lower risk of various chronic diseases, including heart disease and cancer.

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 to vitamin A. This fat-soluble vitamin supports bone growth, vision, and the immune system.

Avoid frying carrots as it has been found to reduce the amount of carotenoid. Cooking carrots with the skin on more than doubles their antioxidant power. You should cook whole carrots before slicing them, as these nutrients cannot escape into the cooking water.

6. Peppers

Peppers are a great source of antioxidants that boost the immune system, especially carotenoids, beta-carotene, beta-cryptoxanthin, and lutein. Heat breaks down the cell walls, making the carotenoids easier for your body to absorb. As with tomatoes, when peppers are cooked or steamed, vitamin C is lost because the vitamin can leach into the water. Try roasting them instead.

7. Brassica

Brassicas, including broccoli, cauliflower, and Brussels sprouts, are high in glucosinolates (sulfur-containing phytochemicals), which the body can convert into a range of cancer-fighting compounds. To convert these glucosinolates into cancer-fighting compounds, an enzyme called myrosinase must be active in these vegetables.

Research has shown that steaming these vegetables preserves vitamin C and myrosinase, thus the cancer-fighting compounds you can get from them. Chopping broccoli and letting it sit for at least 40 minutes before cooking can activate this myrosinase.

Similarly, when cooked, sprouts produce indole, a compound that may reduce cancer risk. Cooking sprouts also break down glucosinolates into compounds known to have cancer-fighting properties.

Chopped broccoli should stand for at least 40 minutes before cooking. Photo: Getty

8. Green beans

Green beans have a higher antioxidant content when baked, microwaved, grilled, or even baked, as opposed to boiled or pressure-cooked.

9. Kale

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.

With all vegetables, higher temperatures, longer cooking times, and larger amounts of water mean more nutrients are lost. Water-soluble vitamins (C and many B vire the most unstable nutrients when it comes to cooking, as they leach from vegetables into the cooking water. So do not soak them in water; use as little water as possible when cooking, and use other cooking methods, such as steaming or roasting. If you have leftover cooking water, use it in soups or gravies, as it contains all the leached nutrients.

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Laura Brown, Senior Lecturer in Nutrition, Food and Health Sciences, Teesside University

This article is republished from The Conversation under a Creative Commons license. Read the original article.