How Cooking Affects the Nutrient Content of Vegetables


Vegetables are key providers of our essential nutritional needs, such as vitamins, minerals, and fibers. As such, different kinds of vegetables are part and parcel of any healthy diet. Vegetables can be served fresh, squeezed and filtered, or cooked by different techniques; but, do vegetables maintain their full nutritional value after cooking?

You may be surprised to know that they already lose some value right after harvest; that is, long before getting cooked. However, vegetables lose much value upon cooking, which is why it is advisable to eat them fresh whenever possible. Moreover, keeping vegetables in the refrigerator in case you will not eat them on the same day lessens the nutritional loss.

Unfortunately, some kinds of vegetables are not edible if not cooked, so they cannot be consumed fresh. Yet, not all cooking techniques have the same effect on the nutritional value; some techniques tend to preserve as much nutrients as possible after cooking.


You can cook vegetables by submerging them in boiling water under different temperatures. A study conducted on broccoli found that over 50% of vitamin C is lost when poached in water. Moreover, poaching negatively affects the glucosinolates compounds that protect our bodies against cancer. Glucosinolates easily dissolve in water; and are, therefore, lost when vegetables are poached. Poaching also affects the nutritional value of leafy vegetables, such as spinach, a large amount of chlorophyll is lost, which is responsible for their green color.


It is undeniable that grilling is among the best cooking techniques used around the world; it gives a unique flavor and a strong taste, not only to vegetables, but also to beef and chicken. Grilling allows us to enjoy healthy foods without boiling them; however, it might cause the loss of some vitamins and minerals, particularly if the vegetables lose their juices during grilling.


Frying food in vegetable or hydrogenated oil is notorious for adding large quantities of complex fats to our food; yet, the harm of frying vegetables does not stop there. Deep frying causes the loss of over 60% of the carotenoids, which are the substances that provide vegetables with their red, orange, or yellow colors as in sweet potato and carrots. Carotenoids are also antioxidants, and therefore, are important for our wellbeing.


This cooking technique was not known decades ago; yet, it has become popular thanks to its speed and the better taste it gives to vegetables. Microwaving does not affect the vegetables carotenoids; however, it causes the loss of much of the glucosinolates and vitamin C. The percentage of losing vital compounds and vitamins depends on the duration and temperature of microwaving.


Steaming is one of the safest and best techniques for cooking vegetables, as it preserves as much vitamins and nutrients as possible. One study found that steaming vegetables causes the loss of only 15% of vitamin C maximum. However, the problem is that the taste of steamed vegetables is not appreciated by many people.

Tips for preserving food nutrients during cooking

  • Do not let vegetables lose their juices while grilling.
  • Poach vegetables in a small amount of water.
  • Do not microwave vegetables under high temperatures and for long durations.
  • When steaming vegetables, add some spices and lemon to obtain a better taste.

Before cooking vegetables, we should always investigate the best technique to preserve as much nutritional value as possible. The used cooking method should not prevent our bodies from the healthy nutrients they would benefit from. Also, taste should not be given priority over value. Last but not least, remember that it is always possible to enjoy tasty food with high nutritional value through following some simple tips.


This article was first published in print in SCIplanet, Winter 2018 issue.

Top Image: Home cooking photo created by senivpetro -

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