Save antioxidants when cooking vegetables

Diet seems to be the crucial part of preventing and even reversing diseases like cancer, heart disease, diabetes and other serious conditions. Because vegetables are a rich source of phytochemicals and antioxidants it is believed that they are especially important for protecting you from diseases. Antioxidant activity is typically measured in fresh produce, but most people eat their vegetables cooked. That leaves the question if cooking vegetables is changing their antioxidant content in any way. In this article you’ll find out:

  • how to get the most antioxidants from cooked vegetables
  • which vegetables are losing the most antioxidants when cooked
  • which commonly used vegetables even increase their antioxidant value after cooking

Cooking methods

There are different ways you can cook vegetables. Some are more gentle to the nutrients in them than others. Common cooking methods include boiling, microwaving, pressure-cooking, grilling, frying, roasting and baking, sauteing, blanching and steaming.

Like it is often the case in the field of nutrition, research with opposing results exist on this topic. For example this study found that total antioxidant activity increased or remained unchanged depending on the type of vegetable but not type of cooking. On the other hand this study found that pressure-cooking and boiling lead to greater losses of nutrients compared to griddling, microwave cooking, baking and frying. As you can see it’s not a simple case of pointing to one cooking method and saying it is the best or worst one.

Why are the research results opposing? That’s because cooking can destroy nutrients in some vegetables but increase the bio-availability of others. Tomatoes and lycopene content before and after cooking are a well known example of this. That’s why it is impossible to pin point any cooking method and claim it preserves or destroys the most nutrients. Simply, every method has its benefits and disadvantages. We’ll cover some of the most common cooking methods and what you should pay attention to when it comes to cooking your vegetables to get the most nutrition out of them.

Boiling

Boiling corn in a pot

Boiling vegetables is achieved when the water in the pot hits 212 °F (100 °C) . At this temperature thermo-sensitive nutrients like vitamin C, vitamin B and polyphenols can be completely destroyed. But the biggest nutrient loss during boiling occurs because under high temperatures water-soluble nutrients like vitamin C leach into the water. This leaves the cooked vegetables void of some valuable nutrients including antioxidants. That’s why it’s best to boil vegetables when you’re making soup, since you’re going to eat the liquid with all the lost nutrients. If you want to eat boiled vegetables and reduce nutrient loss as much as possible use just a small amount of water and cover the pot with a lid during cooking. Shorten the cooking time to keep more nutrients in the food.

The cooking liquid of boiled vegetables is full of nutrients. Don’t through it away. Use it to make soup or as stock liquid.

Pressure cooking

Pressure cooker

Pressure cooking is very similar to boiling. The only difference lies in the time needed to boil vegetables. Under high pressure, the cooking time is significantly reduced up to 70%.  The short cooking time decreases nutrients migration into the water. That way vegetables are left with more nutrients compared to conventional boiling. A study published in the Journal of Food Science concluded that broccoli retained more than 90% of vitamin C after pressure cooking compared to 66% for conventional boiling.

Pressure cooking reduces nutrient leaching into the water compared to conventional boiling.

Microwaving

Micorwaving vegetables

In most studies microwaving vegetables has shown to be a good cooking method. Antioxidant loss is small compared to other cooking methods. In a 2009 study published in the Journal of food science a team of Spanish researchers investigated common cooking methods on 20 different vegetables. They found that microwaving preserved on average 97.3% of the antioxidants in vegetables.

Microwaving vegetables causes minimal antioxidant loss in most vegetables.

Frying

Deep frying vegtables

Frying vegetables in deep oil causes an intermediate loss of nutrients. The big drawback of frying vegetables is the oil content and quality it adds to the vegetables. Frying is especially unhealthy when done in reheated oil. That way a bunch of free radicals and unnecessary calories are added to your food. Frying and deep frying is best avoided if you want to eat healthier vegetables and avoid burdening your metabolism with additional work.

Frying adds unnecessary calories and free radicals from oil to vegetables.

Sauteing

Sauteing vegetables

Sauteing means cooking vegetables with a little bit of oil and adding a small amount of liquid (water, stock, wine,..) over high heat in a short amount of time. This is one of the better cooking methods, because it uses only small amounts of liquids so that the nutrient loss into the cooking liquid is minimal. It also adds a little bit of oil to the veggies which increases the absorption of fat-soluble antioxidants.

Sauteing increases the absorption of fat-soluble antioxidants from vegetables.

Steaming

Steaming vegetables

Steaming vegetables is commonly believed to be a healthy way of cooking because it retains most nutrients. In a study researchers compared antioxidant content after boiling, steaming and frying carrots, zucchini and brocolli. Steaming showed less nutrient loss, especially in health promoting phenol compounds, than the other cooking methods. The main concern with this cooking method is the fact that it doesn’t use any fat during cooking. That makes it difficult for fat-soluble antioxidants to be used by the body. If you don’t want to miss out on these important nutrients, sprinkle a little bit of olive oil over your veggies before you eat them. If you want to limit your fat consumption use an oil mister to add a very thin coating of oil.

Add a little bit of olive oil to steamed vegetables to help absorption of fat soluble antioxidants.

Griddling

Grilling and griddling vegetables

Griddling witch is very similar to grilling has been proved to be a cooking method that causes only low losses of antioxidants. According to the Spanish research team it is very similar to microwaving when it comes to nutrient loss. What you should pay attention to is that griddling is typically done on electric appliances that have anti stick coatings that have been linked to cancer. Use a thick cast iron grill pan instead, to get the same  delicious results but without the dangerous PFOA-s. This type of cooking caramelizes the sugar in your veggies witch gives them a rich flavor.

Griddle your vegetables on cast iron grill pans instead of non stick pans to retain the most nutrients and avoid contamination with cancerous PFOA.

Baking and roasting

Baking vegetables

Baking and roasting are among the better cooking methods as they are are linked to minimal nutrient losses according to the previously mentioned study from Spain. Baking showed minimal nutrient loss in some vegetables and even increase of antioxidants in others. Of course the rule here is to try to shorten the baking time as much as possible to get the best results.

Every vegetable acts differently

As you can see no cooking method is perfect when it comes to retaining nutrients in vegetables. To make it even more complicated not all vegetables behave the same way when exposed to the same cooking methods. Antioxidant content in vegetables after cooking depends both on the type of vegetable and cooking method used. The same cooking method can increase certain antioxidants while deceasing others in the same vegetable. Some of the common vegetables used in western cooking have been researched to find how different cooking methods are influencing the antioxidant content in them. Here is a review for some of them:

Artichokes

Artichoke

You can cook artichokes in any way without any fear of major nutrient loss.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingok-sign
Microwavingok-sign
Pressure-cookingok-sign
Griddlingok-sign
Fryingok-sign
Bakingok-sign

Asparagus

green asparagus

You can cook asparagus as you like just avoid frying.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingok-sign
Microwavingok-sign
Pressure-cookingok-sign
Griddlingok-sign
Fryingavoid-sign
Bakingok-sign

Beets (Beetroot)

beetroot

Beets can be cooked in any way without antioxidant loss.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingok-sign
Microwavingok-sign
Pressure-cookingok-sign
Griddlingok-sign
Fryingok-sign
Bakingok-sign

 

Carrots

Carrots

Carrots even increase their antioxidant value after cooking. Just cook away. They are better cooked than raw.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingok-sign
Microwavingok-sign
Pressure-cookingok-sign
Griddlingok-sign
Fryingok-sign
Bakingok-sign

Cauliflower

cauliflower

Cauliflower is sensitive to boiling. It is also one of the rare vegetables that lose antioxidants in the microwave. Avoid these two cooking methods when it comes to cauliflower.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingavoid-sign
Microwavingavoid-sign
Pressure-cookingok-sign
Griddlingok-sign
Fryingok-sign
Bakingok-sign

Celery

celery

Celery increases antioxidant values after cooking. Just cook on.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingok-sign
Microwavingok-sign
Pressure-cookingok-sign
Griddlingok-sign
Fryingok-sign
Bakingok-sign

Garlic

garlic

Garlic is best consumed raw. It loses most antioxidants when cooked. Add it to your meals for flavor but try to eat some raw too or add it at the end of cooking.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingavoid-sign
Microwavingok-sign
Pressure-cookingavoid-sign
Griddlingavoid-sign
Fryingavoid-sign
Bakingavoid-sign

Green beans

green beans

Keep away the water from green beans. They lose antioxidants during boiling and pressure-cooking. All the other methods actually increase antioxidant content.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingavoid-sign
Microwavingok-sign
Pressure-cookingavoid-sign
Griddlingok-sign
Fryingok-sign
Bakingok-sign

Onions

onions

You can cook them without any fear of loosing nutrients.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingok-sign
Microwavingok-sign
Pressure-cookingok-sign
Griddlingok-sign
Fryingok-sign
Bakingok-sign

Green peppers

green bell pepper

Green peppers are best consumed raw since they miss out on all the cooking methods.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingavoid-sign
Microwavingavoid-sign
Pressure-cookingavoid-sign
Griddlingavoid-sign
Fryingavoid-sign
Bakingavoid-sign

Swiss chard

Swiss chard

Swiss card is also sensitive to thermal processing. Try to eat raw, microwave or griddle for best results.

Cooking methodAntioxidant content
loweredalmost
unchanged
increased
Boilingavoid-sign
Microwavingok-sign
Pressure-cookingavoid-sign
Griddlingok-sign
Fryingavoid-sign
Bakingavoid-sign

Most important

You will get most out of your veggies if you pay attention how you’re cooking them. But the most important thing for the majority is to meet the recommended portions of vegetables every day in any form you like to (except fried veggies, really try to skip those). Although it’s important what’s left in your vegetables after cooking, the benefit of eating any vegetables in any form at all is far greater than to skip them because you don’t know how to cook them.

Photo credit: lightly grilled asparagus, Cooking the Christmas meal, Ginger chicken (3168342551)” by Ginny, the Quick Touch: details & food, Deep Frying, Pressure Cooker – All American Model 910 – with Ball jar, Green beans, SwissChard” by Jonathunder