Posted Dec. 6, 2004
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. The study is scheduled to appear in the December issue of the Journal of the American College of Nutrition.
Davis, of the University of Texas, said demonstrating meaningful changes in nutrient content over a 50-year time interval was a challenge. The researchers had to compensate for variations in moisture content that affect nutrient measurements, and could not rule out the possibility that changes in analytical techniques may have affected results for some nutrients.
"It is much more reliable to look at average changes in the group rather than in individual foods, due to uncertainties in the 1950 and 1999 values," said Davis, who is also a research consultant at the Austin Bio-Communications Research Institute in Wichita, Kansas. "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."
According to Davis, these results suggest a need for research into other important nutrients and foods that provide significant dietary calories, such as grains, legumes, meat, milk and eggs.
"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. "I hope our paper will encourage additional studies in which old and new crop varieties are studied side-by-side and measured by modern methods."
Davis's paper taps into what should be a major and growing concern, according to Chuck Benbrook, science advisor to the Greenfield, Massachussets-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.