How Food Preparation Affects Nutrients

Ann's NOTE: It has been shown that our fruits and vegetables contain uneven amounts of nutrients. Studies point out that food grown on the east coast may contain less selenium than from other areas. Studies have shown that organically grown fruits and vegetables contain more nutrients than commerically-grown, pesticide sprayed produce.

Here is information on how food preparation affects nutrients: (excerpts)from Ralph Moss, Ph. D. Weekly Cancer Decisions, Newsletter #114, 1/04

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.

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. Steaming baby bok choi with Asian mushrooms, or broccoli rabe, collard greens, and endive can be good.

Try adding tofu, cooked brown rice, and some seafood (avoiding those varieties with high mercury content). Season with saffron, sesame oil or tamari sauce.

--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

SOURCE: Ralph W. Moss, Ph.D. Weekly

Newsletter #114 01/04/04

Cooking Methods Affect Broccoli Nutrient Content

Food Additives & Contaminants, 11/06

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