Just as more Minnesota grocery stores go organic, along comes a study from Britain that declares that organic foods contain no more nutrients than conventionally produced foods.

In this systematic and extensive review, published Wednesday in the American Journal of Clinical Nutrition, researchers from the London School of Hygiene and Tropical Medicine searched more than 50,000 papers, identified 162 relevant ones (from as far back as 1958), and then determined that 55 were of sufficient quality to be analyzed.

Although the reviewers found some nutrient differences between the two groups of food (in nitrogen and phosphorus levels, for example), they concluded that those differences were too insignificant to have any impact on health.

They also called for more rigorous research into the factors that determine the nutrient content of food.

It’s all (or mostly) in the timing
I suspect that most committed buyers of organic foods (and I’m one of them) won’t be put off by these findings. The packed-with-more-nutrients argument has always been scientifically iffy. For when it comes to getting the most nutrient bang for your buck from fruits and veggies, other factors regarding the food — what variety it is, how ripe it was when harvested, and when it was harvested — appear to be much more important than whether it’s grown organically or not.

That last factor — how long ago the food was harvested — seems particularly significant. Fruits and veggies are most nutritious as soon as they’re plucked from the garden. After that, senescence sets in, causing the plant’s cells to release proteins that quickly break down the food’s nutrients.

Senescence is why many nutritionists argue for buying local produce, even if it’s not organic, and for eating it as soon as possible after you’ve purchased it. (Refrigeration can slow down senescence, but can’t stop it altogether — as is obvious to anybody who delays cleaning out the vegetable bin in his or her refrigerator.)

The dog that didn’t bark
Of course, the British review didn’t address what’s not in organic food — most notably, pesticides, which have been linked to an increased risk of birth defects, nerve damage, cancer and other health problems, and are a particular concern for children.

The chemical-free claim (and, yes, that claim isn’t fool-proof) is probably the key reason people — particularly parents — choose organic foods over conventional ones, despite the extra cost. But many buy organic for environmental reasons as well: to support farming practices that reduce pollution, conserve water and soil, and protect farm workers from toxic chemicals.

The blogosphere has already begun a vociferous debate about the merits of the British study. But I agree with New York Times columnist ("The Minimalist") and author ("Food Matters") Mark Bittman who pointed out earlier this year that other aspects of the American diet need our attention more:

FYI: Natural food co-ops across the country, including the 15 in Minnesota, are beginning their monthlong "Eat Local, America!" campaign on Saturday (Aug. 1). For more information — and to locate the closest participating co-op to you — check out the campaign’s national website.