Comparison of Cooking Methods and Nutrient Loss




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"The doctor of the future will give no medicine, but will interest his patients in the care of the human frame, in diet and in the cause and prevention of disease."
- Thomas Edison


 Ralph W. Moss, Ph.D. Weekly
 Newsletter #114 01/04/04
High up on my list of New Year's Resolutions is a pledge to eat in a healthful manner in the coming year. I believe that a major key to preventing cancer, heart disease and other catastrophic illnesses is an abundant intake of nutrients, including antioxidants. While supplements sometimes have their place, as I wrote in Antioxidants Against Cancer (2000), it is preferable to get most of our necessary nutrients directly from food. Even the National Cancer Institute urges everyone toeat at least five half-cup portions of fruit and vegetables per day.
 But two studies published late last year suggest that many people may be eating fruits and vegetables that are seriously lacking in vitamins and antioxidants. A test done at one of Spain's major research centers measured the levels of flavonoids (a kind of antioxidant) that remained in fresh broccoli after it was cooked by four popular methods--steaming, pressure cooking, boiling or microwaving. 
 The authors looked at both the total flavonoid content as well as several derivatives in the edible portion of freshly harvested broccoli. The results, they said, "showed large differences among the four treatments in their influence on flavonoid.content in broccoli." Conventional boiling led to a 66 percent loss of flavonoids compared to fresh raw broccoli. And pressure cooking was not much better, with 47 percent of one of the major antioxidants left after cooking (the majority of it was found in the cooking water, which is usually tossed down the drain.) There was a major disadvantage detected when broccoli was microwaved. The loss of flavonoids with that method was an incredible 97 percent! 
 "On the other hand," the Spanish authors wrote, "steaming had minimal effects, in terms of loss" of antioxidants. In fact, there was almost no difference in antioxidants between raw and steamed. "Therefore we can conclude that a greater quantity of phenolic compounds [i.e. compounds with antioxidant activity - ed.] will be provided by consumption of steamed broccoli as compared with broccoli prepared by other cooking processes."
 Blanching and Storing 
 Many people, pressed for time, resort to frozen foods instead of fresh. But what are the effects of blanching foods, i.e., soaking them in hot water, which is commonly done before commercial freezing? In a separate study, Finnish scientists found that blanching and long-term freezing of 20 commonly used vegetables also affected the level of various beneficial compounds in different ways. Blanching, they discovered, destroyed up to one-third of the vitamin C content of vegetables, and this was followed by a further slight loss during
 storage. Folic acid turned out to be particularly sensitive to blanching, with more than half of this important B vitamin being lost, although levels remained stable during freezer storage. Carotenoids and sterols (also common antioxidant compounds) were not affected by either blanching or freezer storage. Dietary fiber was not adversely affected and minerals
 in general were stable. But phenolic antioxidants and vitamins were much more sensitive. There was a 20-30 percent loss of antioxidant activity detected in many vegetables.
 Total Effect
 From this pair of studies we can see that if you buy a package of frozen broccoli in the supermarket and then microwave it according to instructions you will be getting almost NONE of the antioxidants and vitamins you expected from this food. The same is probably true of other vegetables. Blanching and freezing will take away some nutrients, and then harmful (albeit very common) ways of cooking will take away the rest. This has profound implications for the National Cancer Institute's five-a-day fruit and vegetable program. It is clearly not just the QUANTITY of fruits and vegetables that matters but the QUALITY as well. 
 After reading these articles I dusted off my steamer insert and reacquainted myself with the fresh clean taste of food prepared in this way. The best idea is to buy fresh organic produce at the health food store or food coop, and then to steam it until it reaches a degree of "done-ness" that agrees with your digestion and taste. While some cooking is usually desirable, less is better. Try steaming baby bok choi with Asian mushrooms, or broccoli rabe, collard greens, and endive. You can add tofu, cooked brown rice, and some seafood (avoiding those varieties with high mercury content). Season with saffron, sesame oil or tamari sauce and you have a wonderful and easily prepared dish. You will also lose undesired weight, save money on antioxidant pills, and decrease your chances of getting sick. Not a bad payoff from one easy-to-keep New Year's Resolution!
  --Ralph W. Moss, PhD
Vallejo F, Tomás-Barberán FA, García-Viguera C, et al. Phenolic compound contents in edible parts of broccoli inflorescences after domestic cooking. Journal of the Science of Food and Agriculture Volume 83, Issue 14, Pages 1511 - 1516. Published Online: 15 Oct 2003
Puupponen-Pimiä R, Häkkinen ST, Aarni M, et al. Blanching and long-term freezing affect various bioactive compounds of vegetables in different ways. Journal of the Science of Food and Agriculture. Volume 83, Issue 14 , Pages 1389 - 1402 Published Online: 15 Oct 2003
The news and other items in this newsletter are intended for informational purposes only. Nothing in this newsletter is intended to be a substitute for professional medical advice.



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