Foods that contain fat soluble vitamins (vitamin A, vitamin E, vitamin K) or phytonutrients in your food will be absorbed only if the recipe contains some amount of fat. Cooking methods like steaming or saut from a brief period helps retain vitamins and phytonutrients like carotenoids and overcooking destroys both vitamins and phytonutrients. If the cooking method is steaming toss in a little healthy fat (olive oil, sunflower oil) before serving to ensure carotenoid absorption. Example lycopene in tomatoes is absorbed in highest amounts from cooked tomato products that contain a little olive oil.

Source: http://www.gud2eat.com

Steaming Vegetables
A steamer with a built-in timer is the best way to cook vegetables. Most people when boiling their vegetables, throw away the best partthe cooking water. Steaming vegetables conserves the maximum amount of nutrients by subjecting the vegetables to the least amount of heat. Cut your vegetables into small pieces for quicker steaming.

Yes, of Course. They contains much nutritions.