Most cooking methods decrease the amount of vitamins in food. Vitamins are lost to heat, exposure to light and dilution from liquids. But with a little knowledge, you can use cooking methods that help preserve as many vitamins as possible.
Some vitamins are stable in heat. Others, including B and C, are heat-sensitive. A Cornell University study found that spinach lost 77 percent of its folate, a B vitamin, through cooker top cooking. Boiling, frying and roasting are especially hard on heat-sensitive vitamins.
The longer the food is cooked, the more likely it’s losing vitamins. After boiling for two minutes, broccoli loses about 25 percent of its vitamin C; after 11 minutes, 33 percent is lost. The same vitamin loss applies to reheating food or for dishes that are kept hot for a long time, such as on a buffet.
When liquid is added, foods lose more nutrients. Vitamins dissolve into the food, then evaporate or are discarded. Cabbage loses up to 62 percent of its vitamin C when boiled. Boiling robs peeled potatoes of up to 25 percent of their folate.
Vitamins E and C disappear when exposed to air. Exposure to light is harmful to vitamins E, K and A. Folate is lost in storage, and B12 and E are adversely affected if they come in contact with iron or copper.
Ways to preserve vitamins
While it takes some studying to learn the best way to preserve each vitamin, a few general rules apply. Add more raw foods to your diet. Avoid long cooking times. When possible, steam vegetables instead of boiling. Microwaving food preserves vitamins better than most cooking methods, as the food cooks more quickly and doesn’t require added water.
Minerals are more heat-stable than vitamins. But they do leach out if boiled for a long time. Steaming is an effective way to retain minerals as well as vitamins.