Is food becoming less nutritious?
Courtesy the University of Texas at Austin and World Science staff
A study of 43 vegetables and fruits suggests their nutritional value has
declined in the past 50 years, scientists say. The researchers suggested the
decline may result from the fact that farmers have been planting crops designed
to improve traits other than nutritional value, such as size. Broccoli -- a
favorite among many mothers, thanks to its alleged nutritional value -- is one
of the many garden crops whose nutrient content has been declining in recent
decades, according to studies.
The researchers said the study also raises the possibility that similar
declines might have affected other food crops, such as grains. More research is
required to check whether this is so, said Donald Davis, the study's lead
author. The study was designed to investigate the effects of modern agricultural
methods on foods' nutrient content. Davis and colleagues studied U.S. Department
of Agriculture data on garden crops, mostly vegetables, but also melons and
strawberries, comparing data from both 1950 and 1999.
"Considered as a group, we found that six out of 13 nutrients showed
apparently reliable declines between 1950 and 1999." These nutrients included
protein, calcium, phosphorus, iron, riboflavin and ascorbic acid. The declines,
which ranged from 6 percent for protein to 38 percent for riboflavin, raise
significant questions about how modern agriculture practices are affecting food
crops.
"We conclude that the most likely explanation was changes in cultivated
varieties used today compared to 50 years ago," Davis said. "During those 50
years, there have been intensive efforts to breed new varieties that have
greater yield, or resistance to pests, or adaptability to different climates.
But the dominant effort is for higher yields. Emerging evidence suggests that
when you select for yield, crops grow bigger and faster, but they don't
necessarily have the ability to make or uptake nutrients at the same, faster
rate."
"Perhaps more worrisome would be declines in nutrients we could not study
because they were not reported in 1950 -- magnesium, zinc, vitamin B-6, vitamin
E and dietary fiber, not to mention phytochemicals," Davis said.
Davis's paper taps into what should be a major and growing concern, according
to Chuck Benbrook, science advisor to the Greenfield, Massachusetts based
Organic Center for Education and Promotion. The paper is "an important
contribution," wrote Benbrook in a recent email. But he added that he disagreed
with some of Davis' ideas on the reasons for the drop in nutrition. "His sense
is that varietal/genetic differences account for most of the change, but I think
it is likely that production systems also are major contributors, and sometimes
even more important than genetics," wrote Benbrook. In other words, the same
variety of plant may have different nutritional values depending on how it's
grown, Benbrook added.
"The faster a plant grows/is pushed, the more intensive the production
system, the higher the yield goal, the greater the chance that the harvest from
that crop will be deficient in some set of minerals, vitamins, and
antioxidants," Benbrook wrote.
|