The November 2003 issue of the Journal of the Science of Food and Agriculture presented two studies showing how different cooking methods diminished the antioxidant content of vegetables. In one study, researchers in Murcia, Spain, subjected fresh broccoli to four different cooking methods: high pressure boiling, conventional boiling, steaming, and microwaving. In all of these tests they used 5 oz. of broccoli and 2/3 cup of water.
All of the cooking methods resulted in a loss of three types of flavinoids that are cancer-fighting antioxidants. Flavinoids found in brightly colored fruits and vegetables are associated with reducing the risk of heart disease, strokes, and lung cancer. Microwaving the broccoli in water for five minutes led to a 74% to 97% loss of antioxidants. Boiling reduced the flavinoids 66%, while pressure-cooking dropped the loss to 47%.
The healthiest preparation method was to steam the broccoli over water for 3 1/2 minutes leading to a minimal nutrient loss of between 0% to 10%.
Lead researcher Dr. Cristina Garcia-Viguera of the Department of Food Science and Tecnology at CEBAS-CSIC in Murcia, Spain, stated in a news release on October 17, 2003, "Most of the bioactive compounds are water soluble; during heating they leak in a high percentage into the cooking water, reducing their nutritional benefits in the foodstuff. Because of this, it is recommended to cook vegetables in the minimum amount of water (as in steaming) in order to retain their nutritional benefits."
Blanching and Frozen Foods
The blanching process produced a 1/3 loss of antioxidants, including vitamin C. Storing the vegetables in the freezer led to additional nutrient depletion.
Subjecting certain foods to high heat and extreme cold not only diminishes cancer-fighting antioxidants, but may also create cancer-causing chemicals.
French Fries Suffer Indignities
Researchers in Sweden startled the world when they announced in May 2002 that starchy foods cooked at high temperatures contained acrylamide in larger amounts than permitted in drinking water. Acrylamide is used in the manufacture of plastics and was cited in the 1980's as a potential carcinogen in drinking water. Currently the Environmental Protection Agency says that acrylamide in drinking water should not exceed .12 mcg in an 8-oz. serving.
The Swedish scientists stated that acrylamide "causes DNA damage and at high doses neurological and reproductive effects have been observed. Prolonged exposure has induced tumors in rats, but cancer in man has not been convincingly shown."
Fast Food Fries Are Loaded
An order of Wendy's Biggie Fries (5.6 oz.) had 39 mcg, yet 3 oz. of Ore Ida Baked French Fries yielded 28 mcg. Those same Ore Ida fries contain only 5 mcg of acrylamide when they are uncooked.
Only 1 oz. of Pringle's Potato Crisps contained 25 mcg, but corn chips revealed much lower amounts for the same size serving. Fritos Corn Chips registered 11 mcg while Tostitos Corn Chips had 5 mcg. Even breakfast cereals like Cheerios had 6 to 7 mcg per oz.
Although the highest amounts of acrylamide came from potatoes fried or baked at high temperatures, potatoes that were boiled showed less than 3 mcg for a 4 oz. serving.
The World Health Organization's International Agency for Research on Cancer has stated that, based on tests in animals, acrylamide is "probably carcinogenic to humans." American scientists, on the other hand, are skeptical because large doses of acrylamide fed to rats do not prove acrylamide is dangerous to humans. EPA researcher David Lai, who originally reviewed the studies of acrylamide and rats, said, there is "no adequate human data" on acrylamide as a carcinogen. "Based on animal data, we classify acrylamide as a probable human carcinogen. That's all we can say."
Norwegian scientists confirmed the results of Swedish research and warned people to reduce their consumption of potato chips. Their research showed a high level of acrylamide in potato chips, a medium level in French fries, and a low level in breads.
The Bottom Line
Immersing vegetables in a large quantity of water may create nutritient-rich water and vegetables with few nourishing qualities. The irony is that people may be throwing away the most nutritionally valuable part of a meal when they pour the cooking water into the sink.
The most judicious policy may be to eat most servings of fruits and vegetables raw. For cooked foods, steaming briefly in a small amount of water is the best method for preserving most of the antioxidants. Boiling and baking should be less frequent; frying should be eliminated. As for the microwave, its convenience in food preparation does not compensate for the enormous nutrient loss.
When the raw disciples talk about "living foods" and the destruction of enzymes in cooking, we all may want to listen more closely.