Kitchen Gardeners International: Home-grown vitamins and minerals

Looking for another reason why growing some of your own food makes sense? Here's one you might not have considered: nutritional content. While the washed and waxed produce at your local grocery store might look chock full of vitamins and minerals, a recent report in the Journal of HortScience finds otherwise.

Apparently produce in the U.S. not only tastes worse than it did in our grandparents' days, it also contains fewer nutrients - at least according to Donald R. Davis, a former research associate with the Biochemical Institute at the University of Texas, Austin. Davis claims the average vegetable found in today's supermarket is anywhere from 5% to 40% lower in minerals (including magnesium, iron, calcium and zinc) than those harvested just 50 years ago.

Here's a summary of Davis' findings:

1. On the Difficulty of Comparing "Then" and "Now:" Davis is quick to note that historical data can sometimes be misleading, if not altogether inaccurate. Take early measurements of iron in foods: because scientists failed to sufficiently remove clinging soil, iron levels appeared unusually high in certain vegetables like spinach, (which gave rise to the myth that it contained exorbitant amounts of the mineral - a myth further propagated by the popular cartoon character, Popeye). Then again, good historical data provides the only real-world evidence of changes in foods over time, and such data does exist - one farm in Hertfordshire, England, for example, has archived its wheat samples since 1843.

2. On the So-Called "Dilution Effect:" Today's vegetables might be larger, but if you think that means they contain more nutrients, you'd be wrong. Davis writes that jumbo-sized produce contains more "dry matter" than anything else, which dilutes mineral concentrations. In other words, when it comes to growing food, less is more. Scientific papers have cited one of the first reports of this effect, a 1981 study by W.M. Jarrell and R.B. Beverly in Advances in Agronomy, more than 180 times since its publication, "suggesting that the effect is widely regarded as common knowledge."

Less studied, though, is the "genetic dillution effect," in which selective breeding to increase crop yield has led to declines in protein, amino acids, and as many as six minerals in one study of commercial broccoli grown in 1996 and '97 in South Carolina. Because nearly 90% of dry matter is carbohydrates, "when breeders select for high yield, they are, in effect, selecting mostly for high carbohydrate with no assurance that dozens of other nutrients and thousands of phytochemicals will all increase in proportion to yield."

2. On the "Industrialization" of Agriculture: Thanks to the growing rise of chemical fertilizers and pesticides, modern crops are being harvested faster than ever before. But quick and early harvests mean the produce has less time to absorb nutrients either from synthesis or the soil, and minerals like potassium (the "K" in N-P-K fertilizers) often interfere with a plant's ability to take up nutrients. Monoculture farming practices - another hallmark of the Big Ag industry - have also led to soil-mineral depletion, which, in turn, affects the nutrient content of crops.

These findings follow on the heels of others that suggest that supplementing your store-bought veggies with store-bought vitamins and minerals might not be the solution either. When in doubt, grow your own and, if you can't do that, buy from farmers who are taking good care of their soil.

Source: Time Magazine

Posted by KGI on February 19, 2009 1:51 PM to Kitchen Gardeners International
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