Cooking Techniques and the Preservation of Food Nutrients

When it comes to your health, vegetables have superpowers. They help boost your immune system, reduce inflammation and protect against diseases. A bonus? In addition to eating them raw, vegetables can be roasted, boiled, steamed and fried, creating endless cooking and serving opportunities to make the most out of your farmers market bounty.

One question remains: Does cooking vegetables rob you of essential vitamins and minerals? According to Lauren DeWolf, MS, RD, a wellness education specialist, the answer is both yes and no. “The way you prepare vegetables can alter their nutritional quality,” DeWolf says. “How they are altered depends on the vitamin or mineral. While some vitamins can be degraded, some can actually be improved by heating them.”

Water-soluble vitamins, such as B and C, are the most sensitive to cooking methods. These vitamins have a tendency to leach out of veggies when boiled — and can be degraded by heat. Yet fat-soluble vitamins, such as A, D, E and K, fare better during the cooking process. When it comes to minerals, heat can improve the ability of some to be digested, absorbed and metabolized.

Blanching

Blanching is a great technique to help reduce the loss of food quality and maximize its nutritional content. To blanch means to quickly boil and then place the food in a bath of ice water to stop the cooking process suddenly. This technique is especially great for veggies you want to keep a little bit crisp or almost raw. As a result, your vegetables' colors and nutrients will be locked in, and they will stay bright and fresh-looking.

Blanching does the following:

• Destroys microorganisms on the surface of vegetables.
• Softens the vegetable, brightens color, and slows the loss of vitamins.
• Inactivates enzymes which can lead to loss of flavor, color, and texture in frozen produce.

Boiling, simmering, and poaching

Boiling, simmering, and poaching are similar methods of water-based cooking. These techniques differ by water temperature:

• Poaching: less than 180°F (82°C)
• Simmering: 185–200°F (85–93°C)
• Boiling: 212°F (100°C)

Vegetables are generally a great source of vitamin C, but a large amount of it is lost when they’re cooked in water. In fact, boiling reduces vitamin C content more than any other cooking method. Broccoli, spinach, and lettuce may lose up to 50% or more of their vitamin C when boiled. Because vitamin C is water-soluble and sensitive to heat, it can leach out of vegetables when they’re immersed in hot water.

B vitamins are similarly heat sensitive. Up to 60% of thiamine, niacin, and other B vitamins may be lost when meat is simmered and its juices run off. However, when the liquid containing these juices is consumed, 100% of the minerals and 70–90% of B vitamins are retained.

On the other hand, boiling fish was shown to preserve omega-3 fatty acid content significantly more than frying or microwaving.

Grilling and broiling

Microwaving

Microwaving is an easy, convenient, and safe method of cooking. Short cooking times and reduced exposure to heat preserve the nutrients in microwaved food.

In fact, studies have found that microwaving is the best method for retaining the antioxidant activity of garlic and mushrooms. Meanwhile, about 20–30% of the vitamin C in green vegetables is lost during microwaving, which is less than most cooking methods.

Roasting and baking

Roasting and baking refer to cooking food in an oven with dry heat. Although these terms are somewhat interchangeable, roasting is typically used for meat while baking is used for bread, muffins, cake, and similar foods.

Most vitamin losses are minimal with this cooking method, including vitamin C. However, due to long cooking times at high temperatures, the B vitamins in roasted meat may decline by as much as 40%.

Sautéing and stir-frying

With sautéing and stir-frying, food is cooked in a saucepan over medium to high heat in a small amount of oil or butter. These techniques are very similar, but with stir-frying, the food is stirred often, the temperature is higher, and the cooking time is shorter.

In general, this is a healthy way to prepare food. Cooking for a short time without water prevents the loss of B vitamins, and the addition of fat improves the absorption of plant compounds and antioxidants.

One study found that the absorption of beta carotene was 6.5 times greater in stir-fried carrots than in raw ones. In another study, blood lycopene levels increased 80% more when people consumed tomatoes sautéed in olive oil rather than without it. On the other hand, stir-frying has been shown to significantly reduce the amount of vitamin C in broccoli and red cabbage.

Frying

Frying involves cooking food in a large amount of fat — usually oil — at a high temperature. The food is often coated with batter or bread crumbs.

It’s a popular way of preparing food because the skin or coating maintains a seal, which ensures that the inside remains moist and cooks evenly. The fat used for frying also makes the food taste very good. However, not all foods are appropriate for frying.

Fatty fish are the best sources of omega-3 fatty acids, which have many health benefits. However, these fats are very delicate and prone to damage at high temperatures. For example, frying tuna has been shown to degrade its omega-3 content by up to 70–85%, while baking causes only minimal losses.

In contrast, frying preserves vitamin C and B vitamins, and it may also increase the amount of fiber in potatoes by converting their starch into resistant starch.

When oil is heated to a high temperature for a long period of time, toxic substances called aldehydes are formed. Aldehydes have been linked to an increased risk of cancer and other diseases.

The type of oil, temperature, and length of cooking time affect the amount of aldehydes produced. Reheating oil also increases aldehyde formation.

If you’re going to fry food, don’t overcook it, and use one of the healthiest oils for frying.

Steaming

Steaming is one of the best cooking methods for preserving nutrients, including water-soluble vitamins, which are sensitive to heat and water.

Researchers have found that steaming broccoli, spinach, and lettuce reduces their vitamin C content by only 9–15%. The downside is that steamed vegetables may taste bland. However, this is easy to remedy by adding some seasoning and oil or butter after cooking.

Tips to maximize nutrient retention during cooking

Here are 10 tips to reduce nutrient loss while cooking:

• Use as little water as possible when poaching or boiling.
• Consume the liquid left in the pan after cooking vegetables.
• Add back juices from meat that drip into the pan.
• Don’t peel vegetables until after cooking them. Better yet, don’t peel at all to maximize their fiber and nutrient density.
• Cook vegetables in smaller amounts of water to reduce the loss of vitamin C and B vitamins.
• Try to eat any cooked vegetables within a day or two, as their vitamin C content may continue to decline when the cooked food is exposed to air.
• Cut food after — rather than before — cooking, if possible. When food is cooked whole, less of it is exposed to heat and water.
• Cook vegetables for only a few minutes whenever possible.
• When cooking meat, poultry, and fish, use the shortest cooking time needed for safe consumption.
• Don’t use baking soda when cooking vegetables. Although it helps maintain color, vitamin C will be lost in the alkaline environment produced by baking soda.

It May Depend on the Food

Neither a completely raw nor completely cooked diet can be justified by science. That’s because both raw and cooked fruits and vegetables have various health benefits, including a lower risk of chronic disease. The truth is that whether food should be consumed raw or cooked may depend on the food.

Here are a few examples of foods that are either healthier raw or healthier cooked:

Foods That Are Healthier Raw

• Broccoli: Raw broccoli contains three times the amount of sulforaphane, a cancer-fighting plant compound, than cooked broccoli does.
• Cabbage: Cooking cabbage destroys the enzyme myrosinase, which plays a role in cancer prevention. If you choose to cook cabbage, do so for short periods.
• Onions: Raw onion is an anti-platelet agent, which contributes to heart disease prevention. Cooking onions reduces this beneficial effect.
• Garlic: Sulfur compounds found in raw garlic have anti-cancer properties. Cooking garlic destroys these sulfur compounds.

Foods That Are Healthier Cooked

• Asparagus: Cooking asparagus breaks down its fibrous cell walls, making folate and vitamins A, C and E more available to be absorbed.
• Mushrooms: Cooking mushrooms helps degrade agaritine, a potential carcinogen found in mushrooms. Cooking also helps release ergothioneine, a powerful mushroom antioxidant.
• Spinach: Nutrients like iron, magnesium, calcium and zinc are more available for absorption when spinach is cooked.
• Tomatoes: Cooking greatly increases the antioxidant lycopene in tomatoes.
• Carrots: Cooked carrots contain more beta-carotene than raw carrots.
• Potatoes: The starch in potatoes is nearly indigestible until a potato is cooked.
• Legumes: Raw or undercooked legumes contain dangerous toxins called lectins. Lectins are eliminated with proper soaking and cooking.
• Meat, fish and poultry: Raw meat, fish and poultry may contain bacteria that can cause food-borne illnesses. Cooking these foods kills harmful bacteria.

Conclusion

The way you cook your food can affect the nutritional quality of your meal. Some cooking methods can preserve nutrients, while others can cause their loss. To maximize the retention of nutrients, you can use various techniques like blanching, steaming, and sautéing. You can also follow some tips like using less water, consuming the cooking liquid, and cutting food after cooking. Finally, the decision to consume food raw or cooked may depend on the specific food, and there are some foods that are healthier raw, while others are healthier cooked. By making informed choices about cooking techniques, you can help ensure that you are getting the most nutrition out of your food.

Sources:

• Does cooking vegetables change their nutritional value?
• How Cooking Affects the Nutrient Content of Foods
• Is Raw Food Healthier Than Cooked Food?
• How To Cook Your Food for the Biggest Health Benefits