Vitamins come in 2 forms: fat-soluble, which include vitamins A,D, E, and K; and water-soluble, such a vitamins C and B vitamins (thiamin, niacin, riboflavin, and folate). As the name suggests, water-sluble vitamins dissolve in water--either inside your body or on your stovetop.

 

"Fruits and vegetables are 80-90% water," says food biochemist Diane Barrett, PhD, of the Department of Food Science and Technology at the University of California, Davis."You lose the structure of the cells with heat from cooking, and water-soluble nutrients leach into the cooking water." Last year in a review of 56 studies that examined the effects of cooking on nutrient retention, researchers from Barrett's group found that boiled fresh produce on average, loses up to 55% of its vitamin C and 66% of its thiamin in cooking water. If you don't consume the water you do not benefit from the vitamins in it.

 

Steaming helps retain water-soluble vitamins, while boiling surrounds food with water and increases the liklihood for nutrients to leach out, explains Kerry Neville, RD, a spokesperson for the American Dietetic Association (ADA) in Kirkland, Washington, more nutrients remain inside a steamed vegetable since little water is used and there is minimal contact between the food and the water. A study from Denmark's Royal Veterinary and Agriculture University found that boiled broccoli retained only 45-64% of vitamin C after 5 minutes, whereas steamed broccoli maintained 83-100%.

 

Besides the nutritional benefits, steamed vegetables have a pleasing texture if you steam until they are crisp and tender. Limiting the time you cook a fruit or vegetable can also help to preserve its nutrients.