How to Cook Vegetables to preserve nutrients

A diet rich in vegetables is known to be an important part of a well-balanced diet. Vegetables are a good source of minerals and vitamins, which are needed to keep the body functioning properly. In addition, most vegetables are high in fiber and low in carbs and calories, making them beneficial for maintaining normal weight and healthy bowels.

We can all agree that vegetables should be consumed regularly; infact many government health agencies such as the USDA recommend 5-9 servings per day. The question is, how should we be eating our vegetables to get the most nutrition and benefits?

For a while “raw is best” was winning the cooked versus raw vegetable debate. This is because the concentration of nutrients in raw vegetables can change significantly during the cooking process. However, due to the strain that certain raw vegetables can put on digestion, some medical providers are now starting to wonder if the asain cultures, who always consume their vegetables cooked, have it right. 

The purpose of this article is to provide you with information on the positive and negative effects that cooking has on the nutritional value of vegetables and help you to prepare them in the best possible way.


Overall it makes sense to say vegetables should be consumed raw whenever possible to experience the full health benefits from nutrients found within. Cooking vegetables causes them to lose a significant part of their nutritional value because most vitamins and minerals are either sensitive to heat or soluble in water. 

However, new studies show that this is not always the case. For some vegetables, like carrots, cooking them can actually make certain nutrients more available. Which leads to another question; from grilling to boiling to frying, what method should we be using to cook our vegetables? T

Preparation before cooking

When it comes to preparation prior to cooking, washing and peeling are the two actions that affect nutrient levels the most. When presented with the option to wash or soak your vegetables, always wash them! 

Many people soak their vegetables (e.g. potatoes) with the intention of keeping them fresh and protecting them from oxidation, which is the darkening of the vegetable as a result of contact with air. However, soaking has a very negative effect on the nutrients because many of them are water-soluble and can leach into the surrounding water easily. Therefore, rinsing is a much better way to wash vegetables.

Peeling means removing the skin of the vegetable. It is done with the purpose of completely removing all the impurities. This, however, also removes the most nutrient-rich layer of the vegetable. So, avoid peeling your vegetables and cook them with the skin whenever that is possible.

Size matters! Vegetables are usually chopped into small pieces before cooking to increase the cooking time, but this it is not the best method of cooking if you are looking to maximize the use of nutrients. When vegetables are chopped into many small pieces the surface exposed to the negative effects of air and humidity becomes increased.. This means that more nutrients are bound to be lost during cooking. For this reason, vegetables are best to be cooked whole or in largest possible pieces.

Cooking the Vegetables

Vegetables are versatile and can be prepared by boiling, stir-frying, deep-frying, steaming, baking, microwaving, grilling, etc. However, not all of these cooking methods affect the nutrients in the same way and some methods are better for certain types of vegetables while others are worse. We will take a detailed look at all of them and present the pros and cons of each cooking method separately.


Boiling is a cooking method usually perceived by many as being very healthy as it excludes the use of any fats and oils during preparation. However, science shows us that boiled vegetables lose far more vitamins and minerals than vegetables prepared using other cooking methods.

Long exposure to heat and water are to blame for this. Vitamin C, as well as some of the B-complex vitamins, are easily soluble in water. Boiling can cause more than 50% of these vitamins to be lost during cooking.

If the water the vegetables are cooked in is discarded, those nutrients are lost, making boiling the worst method. If however, the water is kept for a soup or broth then some of those nutrients can be preserved and boiling is a reasonable option. 


Steaming is a healthy method to prepare vegetables then boiling because during the steaming process vegetables are exposed to a minimal amount of water.

With steaming the loss of nutrients in vegetables after cooking is lower than 15%. Since the taste is the same but nutritional value is higher, steaming is certainly a better option than boiling, for vegetable preparation. 

Frying (Sautéing)

Frying implies the use of oils or other fats for cooking. Because fats are associated with increased risk of various, mostly cardiovascular, diseases frying is considered to be the least healthy method of food preparation.

When it comes to preserving nutrients in vegetables, frying is not as bad as it might seem. Frying is a quicker process than boiling, this means that heat exposure is shorter. Frying also does not include the use of water and, therefore, causes no loss of water-soluble vitamins.

With frying, you need to be careful to use as little as possible oil. That is why stir-frying is a better choice than deep frying. Also, the choice of oil is important. Some oils, such as olive oil or canola oil, are healthier than others. However, coating the vegetables in flower or batter will help with the preservation of fat-soluble nutrients but will add more calories and carbs to the meal.

Baking and Roasting

During baking, the intense heat of the oven dry-cooks the vegetables. There is no water involved and, therefore, the leaching of the nutrients is brought to a minimum. The same goes for the fats because their use during baking is not necessary.

However, the temperatures inside the oven are very high and the baking process usually lasts longer than boiling or frying. This means that vegetables are exposed to intense heat which can damage and reduce the amount of some nutrients such as B-complex vitamins.

It is good to know that some vegetables, such as onions, potatoes, beet, and celery, are more resistant to heat than others and baking them is a good option.


Grilling is a dry-cooking method of vegetable preparation. In this way, it is similar to baking. However, during baking dry and hot air is used to cook the vegetables. In grilling, a hot board or a grill is used to cook the vegetables and during the process, the vegetables are all the time in contact with the surface.

This causes the liquids filled with nutrients to drip out of the grilled vegetables. Therefore, grilling reduces the nutritional value of vegetables (up to 40%) and even though it is a tasty cooking option it is not the healthiest one.


Microwaving checks all the boxes on the nutrient-friendly vegetables cooking action sheet. It involves a short and low exposure to high temperatures and no water. This means that all the nutrients have a very good chance of survival. The loss of vitamin C in vegetables during microwaving is less than 30%, the least of all cooking methods.


It is understandable that sometimes we need to reheat the food we eat. Some vegetables, such as potatoes, spinach, green peas, eggplant, etc. taste much better when they are warm. However, reheating vegetables means exposing them to high temperatures repeatedly. Since the exposure to high temperature is bad for the nutrients in the first place, repetitive exposure cannot be good for them as well. If you have to reheat your vegetables try to do it using a microwave oven and never do it more than once.


Proper storage can help you to maximize the use of vitamins and minerals naturally found in vegetables. If the vegetables are fresh, they should be stored in cool and dark places. Light, heat, and too much air all have a negative effect on the nutrients.

Some types of vegetables, such as fresh tomatoes, lettuce, cabbage, etc. should be stored in the refrigerator. In this case, the temperature inside the refrigerator should not exceed four degrees Celsius (40 degrees Fahrenheit). 

Other vegetables, such as potatoes and onion, can stay fresh for a long time when stored in dark, dry, and cool storage rooms or cellars in which the temperature can vary between ten and twenty-one degrees Celsius (50 to 70 Fahrenheit).

Another very good way to store vegetables is deep freezing. Frozen vegetables retain most of the nutrients and can last for a very long time if they are kept at a temperature lower than minus eighteen degrees Celsius (0 Fahrenheit). Good examples of vegetables stored in this way are:

  • Broccoli
  • Spinach
  • Sliced bell peppers
  • Chili peppers
  • Green peas
  • Sweet corn
  • Cauliflower

How to Cook the Most Popular Vegetables

Some vegetables are more sought-after than others and all of them can be cooked in a variety of ways. The following is a list of nine best-liked vegetables worldwide and the nutrient-friendly ways to cook them.


Potatoes top the list of most consumed vegetables worldwide. They are commonly used in almost every cuisine and work great as a side dish or a snack. Potatoes cannot be eaten raw, but can be cooked in a variety of ways.

The most popular potato dish is certainly the French fry. These thin, long, and stick-shaped slices of potatoes are deep-fried in oil. Not surprisingly, this very popular method of cooking potatoes is also the least healthy one.

Frequent consumption of fried potatoes over a longer period of time is associated with many health risks, mostly because of the high fat intake caused by deep frying. These risks include:

  • Hypertension
  • Diabetes
  • Stroke
  • Heart disease

Consequently, increased consumption of fried potatoes is associated with an increased risk of premature death.

This is a good example of how the wrong preparation of vegetables can cause them to transform from a potentially healthy food source to the complete opposite.

Potatoes are naturally a good source of vitamin C, vitamin B-complex, potassium, calcium, and iron. They are also low in calories, fat-free and moderately high in fiber, which makes them beneficial for digestion.

In order to use all these valuable nutrients, you need to cook the potatoes in the best possible way. First of all, it is important to preserve the skin of the potato whenever possible. If the potato is sprouting or starting to have “eyes” then you should remove the skin, but, if the skin looks good and clean, leave it.

The second smart thing to do is to leave the potato whole and don’t soak it. A potato prepared like this is best prepared baked, microwaved, or steamed. These cooking methods will help you to prepare the potatoes in the healthiest way.


Tomatoes are used in cooking in various forms. Fresh tomatoes, tomato puree, tomato ketchup, and tomato juice have all found their application in the kitchen.

Fresh tomatoes can be eaten raw and used for the preparation of a variety of delicious fresh salads. When tomatoes are cooked they lose a certain amount of nutrients. Vitamin C is the most vulnerable of these as its loss increases with the duration of cooking and the amount of water used.

However, scientists have found that the levels of lycopene, a potent antioxidant found in tomatoes, increase significantly during cooking. This is an important discovery because lycopene is proven to be many times more efficient in fighting dangerous free radicals than any other antioxidants.


Onions are very heat-resistant and they fall into a group of vegetables that change their nutritional value the least when cooked. Of course, as we have explained earlier in the article, some cooking methods are better than others, but overall onions are healthy both cooked and raw.

Onions are rich in antioxidants, flavonoids, vitamin C, and sulfides which contain essential amino acids. The outer layers have more of these nutrients than the inner ones so keep that in mind when you clean and prepare these vegetables.

Cooking can reduce the levels of nutrients in onions. Sulfides are the most vulnerable and their levels drop significantly as a result of cooking.

Sweet Corn

Sweet corn is a very good source of many essential nutrients including; sodium, potassium, calcium, magnesium, iron, and Vitamin B6. One thing that all of these nutrients have in common is that they are soluble in water.

Unfortunately, this means that the levels of these nutrients are greatly influenced by cooking. Boiling, for example, can severely reduce (by 50%) the levels of essential nutrients in sweet corn.

Other methods of cooking such as baking are somewhat better. However, since corn requires a long time to cook the loss of nutrients remains significant due to long exposure to intense heat.

Chili Peppers

Chili peppers are widely used in many cuisines because of the distinctive hot flavor they give to food. These vegetables are more than just a spicy addition to various dishes. Chili peppers are rich in antioxidants and various bioactive compounds that are considered to be beneficial for health. Capsaicin is the best known of these compounds. It is often associated with weight loss, pain relief, and other health benefits.

Capsanthin, ferulic acid, sinapic acid, and violaxanthin are potent antioxidants that are also present in chili peppers.

The levels of capsaicin do not change significantly when chili peppers are cooked, while the levels of antioxidants actually increase.


Broccoli is a vegetable famed for its health benefits. Raw broccoli is simply packed with precious minerals and vitamins. The minerals found in broccoli include:

  • Magnesium
  • Iron
  • Calcium
  • Selenium
  • Manganese
  • Phosphorus
  • Selenium

Luckily, these are rarely affected by all cooking methods except boiling. If you prepare your broccoli by baking, steaming, or grilling you will get the biggest part of its minerals.

Vitamins are a different story though. Broccoli is rich in vitamin A, vitamin B6, vitamin C, vitamin E, and vitamin K. Some of these vitamins are water-soluble (vitamin C and B6), so cooking can decrease their amount in broccoli significantly.

Some nutrients can also be made more available by cooking. Vitamin A found in broccoli, for example, is released by cooking.


When it comes to the content of protein, carbs, and fats, raw and cooked carrots are very similar. Cooked carrots end up with a few calories more than their raw counterparts (55 compared to 52 calories per cup). Protein and fat levels remain pretty much the same, while carbs and dietary fibers increase a little.

Vitamin C and B-complex vitamins levels decrease slightly with cooking, but, vitamin A and lutein levels increase.

Cooking also increases the levels of iron, calcium, phosphorus, and magnesium, while it decreases the levels of potassium in carrots.


Cauliflower is very low in calories and therefore it is not a significant source of proteins, carbs, or fats. It is, however, a good source of vitamins and minerals, such as:

  • Vitamin C
  • Vitamin B-complex
  • Vitamin K
  • Magnesium
  • Potassium
  • Manganese
  • Phosphorus

Cauliflower can be eaten raw but most people prefer its taste when it is cooked. Cooking methods that include the use of water are not a good option for the preparation of cauliflower because they drain most of the nutrients, including protein.

The best ways to cook cauliflower are microwaving, sautéing, and steaming. Adding some healthy oils and citrus juices can also help to increase the availability and absorption of cauliflower-based nutrients.


Cabbage is a very good source of dietary fiber, as well as vitamin A, vitamin B6, vitamin C, calcium, and potassium. It can be eaten raw and it is often used for salads. Many people prefer the flavor of raw cabbage overcooked one. However, cabbage (including sour cabbage) is an important ingredient in many cuisines.

Boiling the fresh cabbage will not only cause most of the nutrients to leach, it will also change its taste for worse if done for too long.

The best, nutrient-friendly, ways to cook fresh cabbage are steaming and baking. These methods will help to preserve the nutrients as much as possible. However, you might consider adding some salt, pepper, olive oil, animal fats or lemon juice to improve the flavor.

A Few Additional Tips

There are some tips for cooking vegetables that can help you to maintain the nutrients and make your food taste better. The following are three such tips:

A little fat is not a bad idea

Cooking vegetables in moderate amounts of fats, in many cases can help us access nutrients and fat soluble vitamins even better. Vitamins D and K, as well as beta carotene, require fat to transfer them into the bloodstream. Using some fat or oil while cooking your vegetables (e.g. stir-frying), will benefit the absorption of these nutrients. The finished dish will taste much better too.

Go easy on the water

Water extracts and absorbs all the nutrients that are water-soluble. If you cannot avoid cooking with water, use as little as possible and keep the cooking time to a minimum. You can also use the water, in which the vegetables were cooked, as a broth. Cold water is almost as bad as boiling water. So, soaking and cooling are also not welcome.

Add citrus fruits

Not all vegetables have the same composition. For this reason, they are all digested differently. During the digestion process, some nutrients are absorbed more easily compared to others. Iron found in vegetables, for example, can often pass through the digestive tract without being absorbed. This can be a specifically serious problem for people on a vegan or a vegetarian diet as it can lead to anemia (iron deficiency). Vegetables known to be rich in hard-to-absorb-iron are:

  • Kale
  • Spinach
  • Broccoli
  • Swiss chard

Consummation of citrus fruits and their use in cooking can greatly improve the absorption of iron from vegetables. This is because the vitamin C found in citrus fruits is capable of having a chemical reaction with the iron. The result of this chemical reaction is a transformation of iron into a form easily absorbable by our digestive system.

Therefore, some orange, lemon, lime, or grapefruit is more than welcome as an addition to you sautéed, steamed, or stir-fried vegetables.

The Final Word

While some vegetables have to be cooked before eating, others can be consumed raw. However, most vegetables are somewhere in the middle. This means that although they can be consumed raw, cooking and combining these vegetables with other types of food makes them taste significantly better and often more nutritious. 

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