Last weekend's Observer Magazine had an interesting article by Dr. John Briffa on the best way to cook vegetables if you want to preserve nutrients. Surprisingly, he cites a paper in the Journal of the Science of Food and Agriculture which reports that microwaved vegetables lose 74-97% of three major antioxidant compounds that are believed to be cancer-fighting compounds. (Steamed broccoli lost only 8-11% of the same compounds.) According to Dr. Briffa, the common assumption has always been that as microwaving does not use water to cook vegetables it must be healthier than traditional cooking methods. This report is one of the first to check that theory.
Less surprising is the study's conclusion that the less water you use to cook vegetables the more you will retain nutrients. Dr Cristina Garcia-Viguera, co-author of the study, explains these results: "Most of the bioactive compounds are water soluble; during heating they leach in a high percentage to the cooking water, reducing their nutritional benefits in the foodstuff." It follows then that the best way to retain as much goodness as possible in your veggies is to steam them. One other interesting conclusion of the study: frozen vegetables retain more vitamin C if they are placed directly in boiling water instead of being thawed first. Luckily this fits in well with my slapdash last-minute cooking style!
Oh and don't forget to save that boiled water for your soups...the nutrients aren't lost forever! (Honesty does force me to point out, however, that the broken down cancer-fighting compounds probably are...)