Article: Declining Fruit and Vegetable Nutrient Composition: What is the Evidence?
Author: Davis, D.R.
Publication: HortScience Vol. 44(1) February 2009
We often hear claims that minerals in both our food supply and our soil have been declining for the past several decades. Soils poor in minerals are a consequence of poor land stewardship, the argument goes, and as a result the quantities of vitamins and minerals in our food have also declined. What research evidence exists to support this argument?
The article cited above is one of the few peer-reviewed articles that directly address this topic. This article “summarizes three kinds of evidence pointing toward declines during the last 50 to 100 years in the concentration of some nutrients in vegetables and perhaps also fruits available in the United States and the United Kingdom.”
The first type of evidence presented deals with the “dilution effect” of synthetic fertilizers. Research trials have compared mineral content of fertilized plants and unfertilized plants, concluding: “…fertilized plants contained larger amounts of minerals than the unfertilized plants, but these amounts were sufficiently diluted by the increased dry matter that all mineral concentrations declined, except for P.”
Comparisons of historical measurements are another type of evidence presented. Statistical comparisons of older data (50 to 70 years) with current data reveal a similar trend of decline:
The strongest evidence for declines occurs for minerals in vegetables, especially calcium and copper (Cu), with median declines of ~17% and 80%…The one study that considered protein and vitamins found apparent median declines in 43 garden crops (nearly all vegetables) amounting to 6% for protein and 15% to 28% for three of the five vitamins studied.
Similar studies show statistically significant declines in potassium, manganese, zinc, copper, magnesium, calcium, phosphorous, and iron.
Data analysis reveals, however, that these trends are not necessarily well explained by soil mineral depletion. Natural variability between cultivars may be responsible for declines in nutrient densities. The author compares four side-by-side studies in order to test this hypothesis. He concludes that these studies:
show uniformly inverse associations between yield and nutrient concentrations for every nutrient studied so far (other than carbohydrate) – two minerals in broccoli; six minerals in wheat, plus protein, oil; and three amino acids in maize. These four studies suggest to me that genetic dilution effects may be common when selective breeding successfully increases crop yields.
The author explains the apparent reason for these consistent declines in mineral and nutrient concentrations:
In fruits, vegetables, and grains, usually 80% to 90% of the dry weight yield is carbohydrate. Thus, when breeders select for high yield, they are, in effect, selecting mostly for high carbohydrate with no assurance that dozens of other nutrients and thousands of phytochemicals will all increase in proportion to yield. Thus, genetic dilution effects seem unsurprising.
Davis’ explanation for declines in food nutrient densities is certainly plausible, and supported by the evidence. While current available data does little to support the hypothesis that declines in soil minerals are causing the decline in food quality, more research is required in this area to ascertain the true nature of the relationship between land management and nutrient densities in food. The research of Dr. Kristine Jones on the pasture cropping techniques of Colin Seis indicate massive changes in soil mineral content associated with a shift to pasture cropping; the effect that these changes may have on our food supply is still poorly understood.
What is clear, however, is that plant breeding programs have had the unintended consequence of reducing our food quality; this evidence highlights yet another reason why our agricultural biodiversity is such an important resource for the future of food production.
Makala: Kupungua kwa Viungo vya Chakula cha Matunda na Mboga: Uthibitisho Ni Nini? Mwandishi: Davis, D.R. Uchapishaji: HortScience Vol. "Mwanzoni mwa mwaka wa 2009 tulipata taarifa kwamba ""minerals katika chakula na udongo wetu zimekuwa zikipungua kwa miongo kadhaa iliyopita.""" """Uchumi wa madini katika udongo ni matokeo ya usimamizi mbaya wa ardhi, na kwa sababu hiyo kiasi cha vitamini na madini katika chakula chetu pia kimepungua." Ni uthibitisho gani wa utafiti uliopo unaounga mkono hoja hii? Makala iliyotajwa hapo juu ni mojawapo ya makala chache zilizochunguzwa na wenzao ambazo zinazungumzia moja kwa moja mada hii. "Hii makala ""ina muhtasari wa aina tatu za ushahidi zinazoelekeza kuelekea kupungua kwa miaka 50 hadi 100 iliyopita katika mkusanyiko wa virutubisho fulani katika mboga na labda pia matunda yanayopatikana nchini Marekani na Uingereza."" Aina ya kwanza ya ushahidi iliyotolewa inahusu ""athari ya kupunguzwa"" ya mbolea za synthetic." Utafiti wa utafiti umepima kiasi cha madini katika mimea iliyotengenezwa kwa mbolea na mimea isiyo na mbolea, na kuhitimisha: mimea iliyotengenezwa kwa mbolea ilikuwa na kiasi kikubwa cha madini kuliko mimea isiyo na mbolea, lakini kiasi hicho kilipunguzwa kwa kiasi kikubwa na kuongezeka kwa vitu kavu, hivyo viwango vyote vya madini vilipungua, isipokuwa P. "Ulinganisho wa takwimu za zamani (50 hadi 70 miaka) na data ya sasa inaonyesha mwelekeo sawa wa kupungua: ""Ushahidi mkubwa wa kupungua hutokea kwa madini katika mboga, hasa kalsiamu na shaba (Cu), na kupungua kwa wastani wa ~ 17% na 80%"" - utafiti mmoja uliozingatia protini na vitamini uligundua kupungua kwa wastani katika mazao 43 ya bustani (karibu mboga zote) kwa asilimia 6 kwa protini na asilimia 15 kwa asilimia 28 kwa vitamini tano." Uchunguzi kama huo unaonyesha kupungua kwa kiasi kikubwa kwa potasiamu, manganese, zinki, shaba, magnesiamu, kalsiamu, fosforasi, na chuma. Hata hivyo, uchambuzi wa data unaonyesha kwamba mwenendo huo hauelezi waziwazi kwa sababu ya kupungua kwa madini ya udongo. Tofauti ya asili kati ya aina inaweza kuwa na jukumu la kupungua kwa wiani wa virutubisho. Mwandishi anakabiliana na masomo manne yaliyofanywa pamoja ili kupima nadharia hiyo. "Kama matokeo, utafiti huo ulionyesha ""mshirika wa kawaida wa kinyume"" kati ya mavuno na viwango vya virutubisho kwa kila virutubisho vilivyochunguzwa hadi sasa (badala ya wanga): madini mawili katika broccoli, madini sita katika ngano, pamoja na protini, mafuta, na asidi tatu za amino katika mahindi." Uchunguzi huu wa nne unaniambia kwamba athari za upungufu wa maumbile yaweza kuwa za kawaida wakati uzalishaji wa kuchagua unafanikiwa kuongeza mavuno ya mazao. "Mwandishi wa kitabu hiki anaeleza sababu ya kupungua kwa kiasi cha madini na virutubisho: ""Kwa kawaida, katika matunda, mboga na nafaka, asilimia 80 hadi 90 ya uzito wa kavu ni wanga." Kwa hivyo, wakati wafugaji wanapochagua kwa mavuno ya juu, wao ni, kwa kweli, kuchagua hasa kwa wanga wa juu bila uhakika kwamba vijumla vingine vya virutubisho na maelfu ya phytochemicals yote yataongezeka kwa uwiano wa mavuno. Kwa hiyo, athari za kupunguzwa kwa chembe za urithi hazishangazi. Davis'maelezo ya kupungua kwa wiani wa virutubisho vya chakula ni hakika ya kuaminika, na inasaidiwa na ushahidi. Ingawa data zilizopo sasa hazitegemezi sana nadharia ya kwamba kupungua kwa madini ya udongo husababisha kupungua kwa ubora wa chakula, utafiti zaidi unahitajika katika eneo hili ili kuamua asili halisi ya uhusiano kati ya usimamizi wa ardhi na wiani wa virutubisho katika chakula. Utafiti wa Dr. Kristine Jones juu ya mbinu za kilimo cha malisho ya Colin Sears unaonyesha mabadiliko makubwa katika maudhui ya madini ya udongo yanayohusiana na mabadiliko ya kilimo cha malisho; athari ambazo mabadiliko haya yanaweza kuwa nayo kwenye ugavi wetu wa chakula bado haijulikani. "Lakini, ni wazi kwamba mipango ya uzalishaji wa mimea imekuwa na matokeo yasiyotarajiwa ya kupunguza ubora wa chakula chetu, ushahidi huu unaangazia sababu nyingine kwa nini utofauti wetu wa kibiolojia wa kilimo ni rasilimali muhimu kwa siku zijazo za uzalishaji wa chakula. """