Speaking of heirloom tomatoes, everyone will tell you that the tomatoes of their youth tasted better than they do today. Depends on the tomato, I’m sure, but in general that seems a safe bet, especially if you’re comparing something ugly fresh-picked from the garden with a supermarket beauty. Now, it seems, the older variety may have packed a superior nutritional punch too.
A fascinating paper to be published in HortScience Review by Donald R. Davis, who recently retired from the University of Texas, compares the mineral content of fruits and vegetables over the past 50 years or so. Davis looks at three types of evidence. First, the so-called dilution effect: the more yields increase, thanks to fertilizers, irrigation and other external inputs, the lower the concentrations of many minerals in the harvested part. Secondly, looking at historical food composition tables, older measurements tend to be higher than new ones, for many fruits and vegetables. Third, and most interesting, side-by-side comparisons of old and new varieties, grown today and measured in identical fashion, also show declines from old to new. This is effectively a “genetic” dilution effect. The increase in yield has been achieved by genetic selection, not environmental inputs, but the impact seems to be the same.
These last are perhaps the most convincing. Alas, they are also the most scarce. Broccoli varieties show a decline in calcium and magnesium. Wheat varieties likewise showed a decline in minerals, protein and oil from older varieties to newer. And three amino acids were lower in modern maize varieties than in older selections. Davis writes:
Recent studies of historical nutrient content data for fruits and vegetables spanning 50 to 70 years show apparent median declines of 5% to 40% or more in minerals, vitamins, and protein in groups of foods, especially in vegetables. Although these apparent declines in individual nutrients may be confounded by systematic errors in historical data, the broad evidence is consistent with more definitive studies and seems difficult to dismiss.
Without getting into the reasons for these results — almost certainly they relate to the fact that recent breeding efforts seldom target nutrients — one thing seems clear. More data would be useful. Would it be too much to ask genebanks, who often regenerate a time-series of accessions in a single year, to consider making part of the harvest available for detailed chemical analysis?