Donald Davis, a scientist retired from the University of Texas at Austin, and his colleagues published a study in 2004 comparing U.S. Department of Agriculture data on vegetable nutrients from 1950 to data from 1999, and found notable decreases, particularly for key nutrients like calcium, iron, phosphorus, riboflavin, and ascorbic acid.
Davis believes that the primary reason for the decrease is selective breeding: As growers and researchers have spent the last 50 years trying to produce varieties of crops that yield more fruit, they’ve been ignoring the effects on nutrient content. Davis cites a few studies that compared high-yield varieties to non-high-yield varieties in the same soil and growing conditions, and found decreased nutrient content in the former.
“It’s early evidence, but that’s very powerful evidence because the soil is the same; the only difference is the genetics of the plant,” Davis says.
The studies show that as fruits and vegetables get bigger and more plentiful, nutrients get diluted. Some high-yield varieties are “dwarf” plants, meaning the plants themselves are smaller. But plants draw in and store minerals in their stalks, and when it comes time to create a fruit or vegetable, the plants extract the minerals and transform them into beneficial nutrients in the fruit. A lack of storage space for nutrients in the stalk translates to a loss of nutrients in the fruits. (Because taste is so subjective, not much research has been done flavor loss in high-yield varieties. But some people anecdotally claim that flavors in high-yield varieties also seem diluted compared to heirlooms — varieties that have been passed down, unaltered, through generations.)
Though Davis believes the issue is a serious problem, he cautions against panic. Nutrient depletion pales as a threat when compared to other aspects of the American diet — namely, our preference for refined sugar, fats, oils, and refined grains over fruits and veggies in the first place.
“This is just one more reason to eat more of our current fruits and vegetables, because they’re still our best source of many nutrients even after this apparent decline,” he says.
For those who want to grow their own food, Davis recommends looking for heirloom and non-hybrid varieties of plants, which may not yield as much food, but are probably more nutritious, and possibly more flavorful.
“Some of the best flavor tomatoes that I know of that I’ve grown at home are the little ones, the littler cherry tomatoes,” he says.
How much have our nutrients been depleted? Check out this infographic showing the changes in nutritional content of a few common vegetables:
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