How Cooking Methods Affect Vegetable Nutrition

Carlene Thomas is a dietitian, a person who gives advice about healthy foods to eat. When it comes to eating healthy vegetables, Thomas says there are two kinds of people who ask her for advice. The first kind wants to know how different cooking methods affect the nutrition in vegetables. The other kind of person wants to know how to eat more vegetables. Thomas’ simple answer to both groups is this: The best vegetables are the ones you actually want to eat.

Thomas told the Associated Press that many people buy vegetables that they think they will eat. Maybe the produce is popular or someone is bringing attention to it on social media. But then they end up not using it. That means the vegetable gets thrown away after it goes bad. In that case, Thomas said, “It doesn’t matter how you cook them, because if they’re going in the trash, they’re not in your body.”

However, Thomas said research shows cooking methods do affect nutrition. But it is not as simple as comparing raw, or uncooked, vegetables to cooked ones. Cooking methods can include steaming, roasting, boiling, or sauteing. So, are raw vegetables healthier than cooked? Not always. When vegetables are cooked with high heat for a long period of time many nutrients break down. However, cooking softens the cell walls in vegetables, making them easier for the body to digest. Cooking changes the structure of vegetables which increases what dietitians call bioavailability. This is the body’s ability to use the nutrients in vegetables, Thomas said.

Cooked food is often more nutritious than raw food. For example, cooked tomatoes release more of the antioxidant lycopene than raw tomatoes, she said. Lycopene is believed to have qualities that prevent cancer. Also, cooked carrots have more beta-carotene that can be absorbed by the body. Roasting pumpkins, carrots and sweet potatoes increases available carotenoids. These antioxidants are thought to prevent inflammation in the body.

Which cooking methods are the healthiest? However, the shorter the cooking time, the more nutrients are kept in the food. That advice comes from Amber Pankonin, a dietitian in the U.S. state of Nebraska. Cooking over boiling water, or steaming, and in a microwave are considered the most nutritious methods. These two methods use little time and require no fat.

Another healthy method is blanching. This is when you boil vegetables in water for a minute or two. But not too long. Boiling vegetables runs the risk of losing water-soluble nutrients including vitamin C, B1 and folate. Thomas explained the reason boiling is not good for vegetables: The nutrients are "... leaching into the water, and you’re tossing out the water.” However, you could save the water from boiled vegetables and use it for other purposes, such as soups, or just drink it.

What about taste? Dietitians say there is no problem using a small amount of fat. Besides making vegetables taste better, a little cooking oil helps the body to absorb fat-soluble vitamins, said Pankonin. That means more vitamin A from squash, carrots, and sweet potatoes; more vitamin D from mushrooms; more vitamin E from bell peppers, leafy greens and asparagus; and more vitamin K from greens, broccoli and onions.

For pan frying or sauteing, Pankonin suggests cooking with enough oil so the vegetables do not stick to the pan. The amount of oil will depend on the quantity of vegetables and the size of the pan. For roasting, you will likely need more oil. Despite the longer cooking time, roasting will still keep some nutrients and will increase the flavor with the heating of natural sugars. “Flavor is king,” Pankonin said. “I would much rather see people roasting their vegetables and enjoying them.”