Posted November 28, 2011
Vegetables are healthy food bristling with vitamins, minerals and carbohydrates and they should be on everyone’s plate everyday.
Each type of vegetable offers its own nutritive substances and people can cover their nutritional needs by eating a variety of them, said Silke Restemeyer of the German nutrition organization. Thus, an A (as in aubergine) to Z (as in zucchini) approach is best for getting the most out of the wide variety of vegetables.
Nutritionists warn, however, that vegetables can lose a lot of their nutritional value when they are cooked. They agree that steaming is the best way to prepare them, but they also note that of the recommended five portions of vegetables and fruits a person should eat, at least one should be raw or in a salad.
“Basically, uncooked vegetables are the richest in vital substances,” said Restemeyer.
But of course, people can eat whatever tastes best to them. For some that means lightly steamed, while others would rather have them stewed, braised, grilled or roasted. And while one person likes them well-seasoned, another prefers them in a cream sauce.
Heat is what causes vegetables to lose their nutrients, but there is a big difference between the extent to which they are lost depending on the cooking method used.
“Among the most nutrient-preserving ways to cook vegetables are steaming, cooking them in their own juices or with just a little bit of water, wine or broth,” said Margret Morlo of an association in Germany devoted to nutrition and diet.
The reason is not solely that many vitamins, including C and B1, as well as all minerals are water-soluble and because these methods use little water the vitamins and minerals remain in the food. Usually, they are steamed at a low temperature and only until the vegetables are al dente. Steaming them at a high heat for too long destroys their nutritional content.
Vegetables such as carrots retain a similar amount of their nutrients when they are cooked in water. This can be done in a steamer or in a regular pot with a vegetable sieve. Another way to preserve nutrients is to cook the vegetables in hot oil in a skillet or wok until the vegetables are al dente.
Yet another alternative is to marinate the vegetables and then grill them or roast them in the oven for 30 minutes, said Carsten Voigt of an association for cooks in Germany. “These methods are equally as protective of the nutrients and you obtain a delicious roasted flavour,” he said.
The cooking methods that cause the greatest loss of nutrients are slow cooking in a lot of liquid at high temperatures – 75 to 95 degrees Celsius – and classic simmering. Shorter cooking times mean fewer vitamins are lost compared with longer cooking times, said Voigt. In addition, cooking experts recommend using as little liquid as possible because the more liquid in the pot, the greater amount of minerals lost.
For the same reason vegetables shouldn’t be cut in small pieces or peeled before being prepared. “Removing the peel is a shame because it contains the highest vitamin content and the most flavour,” said Voigt.
There are a few other tricks that can minimize the loss of nutrients. “The lid should be tightly closed and seldom opened when cooking vegetables so that as little of the nutrients as possible can evaporate,” said Morlo. The water remaining in the pot, along with any nutrients that it has absorbed, can be used in a sauce or broth poured over the vegetables.
Cooks also should be aware that not every way to cook vegetables is appropriate for every type of vegetable. Firm vegetables such as beetroot are best suited for cooking, while soft vegetables such as broccoli should be steamed. The question of whether to cook a vegetable or eat it raw also depends on the type.
Some vegetables such as cabbage become more digestible when cooked. Raw green beans, for example, must be cooked for 10 minutes at 100 degrees Celsius to neutralise a protein that can be toxic if consumed by humans. In addition there are nutrients in plants that the body can make better use of when cooked. These include secondary nutrients such as lycopene in tomatoes.
Ripeness is another factor in ensuring that vegetables have as many nutrients as possible. They are at their peak in terms of nutrition when they are ripe and fresh. Finally, vegetables should be stored in a cool, dry and dark place.