Historical changes in the mineral content of fruits and vegetables

Historical changes in the mineral content of fruits and vegetables Anne-Marie Mayer Independent Researcher, Devon, UK Implies that a balance of the different essential nutrients is necessary for maintaining health. The eight minerals that are usually analysed are Na, K, Ca, Mg, P, Fe, Cu, Zn. A comparison of the mineral content of 20 fruits and 20 vegetables grown in the 1930s and the 1980s (published in the UK Government’s Composition of Foods tables) shows several marked reductions in mineral content. Shows that there are statistically signifi cant reductions in the levels of Ca, Mg, Cu and Na in vegetables and Mg, Fe, Cu and K in fruit. The only mineral that showed no signifi cant differences over the 50 year period was P. The water content increased signifi cantly and dry matter decreased signifi cantly in fruit. Indicates that a nutritional problem associated with the quality of food has developed over those 50 years. The changes could have been caused by anomalies of measurement or sampling, changes in the food system, changes in the varieties grown or changes in agricultural practice. In conclusion recommends that the causes of the differences in mineral content and their effect on human health be investigated. British Food Journal 99/ 6 [ 1997] 207–211 © MCB University Press [ ISSN 0007-070X] Th e pu r pose of th is pa per is to a ddr ess th e qu estion : h a s th e n u tr ition a l qu a lity (pa r ticu la r ly essen tia l m in er a l con ten t) of fr u its a n d ve geta bles ch a n ged th is cen tu r y du r in g th e per iod of ch a n ges in th e food system a n d m oder n iza tion in a gr icu ltu r e? Th e UK Gover n m en t’s Com position of Food s da ta pr ovides a sou r ce of da ta a t two tim e poin ts sepa r a ted by a ppr oxim a tely 50 yea r s; by com pa r in g th is da ta I a ttem pt to a n swer th is qu estion . The composition of foods tables Th e fir st edition of th e UK Ch em ica l Com position of Food s[1] a r ose fr om a n eed to pr ovide in vestiga tor s w ith in for m a tion for a w ide r a n ge of foods con su m ed in th e UK. Th e da ta on fr u it a n d ve geta bles wer e com piled fr om pr eviou s stu dies of th e com position of foods[2]. Un for tu n a tely, th ese r epor ts wer e destr oyed in a fir e du r in g th e Secon d Wor ld Wa r a n d h ave been ou t of pr in t ever sin ce. Th is m ea n s th a t exa ct da tes or deta ils of th e a n a lyses a r e n ot k n ow n . Sin ce th e fi r st edition th er e h ave been fou r su bsequ en t u pda tes of th e fu ll Com position of Food s ta bles. It w a sn ’t u n til th e fi fth edition , h owever, th a t th e ta bles in clu ded su bsta n tia l r evision s of th e or igin a l da ta on fr u its a n d ve geta bles th a t wer e listed in th e fi r st edition . Th e fifth edition of T h e Com position of Food s[3] a ddr essed a n eed for u pda tes of th e old da ta . Th e in tr odu ctor y section sta tes “Th e n u tr ition a l va lu e of m a n y of th e m or e tr a dition a l foods h a s ch a n ged. Th is ca n h a ppen wh en th er e a r e n ew va r ieties or n ew sou r ces of su pply for r aw m a ter ia ls; w ith n ew fa r m in g pr a ctices wh ich ca n a ffect th e n u tr ition a l va lu e of both pla n t a n d a n im a l pr odu cts…” Th e u pda ted com position s of fr u its a n d ve geta bles a r e ba sed on a n a lytica l stu dies com m ission ed by th e Min istr y of Agr icu ltu r e, F ish er ies a n d Food (MAF F ). Th e sa m ples wer e design ed to r efl ect th e u su a l pa tter n of con su m ption in th e UK a t th e tim e of a n a lysis. Th e ta bles a r e n ot design ed to pr ovide com pa r a tive h istor ica l da ta – th e fr u it a n d ve geta bles wou ld n ot n ecessa r ily h ave been gr ow n in sim ila r con dition s, soils, or tim es of yea r or be of th e sa m e va r ieties. Th e da ta wer e a lso pr ovided by m ixed sou r ces (see below ). Mor e con tr olled da ta wou ld h ave been better, bu t th is da ta n ever th eless pr ovides a good sta r tin g poin t for th e com pa r ison . Th e u pda ted ve geta ble a n a lyses wer e ca r r ied ou t by th e In stitu te for Food Resea r ch between 1984 a n d 1987 a n d h ave been u sed for a ll th e ve geta ble m in er a l da ta . Th e u pda ted fr u it a n a lyses wer e ba sed la r gely on da ta fr om th e La bor a tor y of th e Gover n m en t Ch em ist (LGC). Most of th e twen ty fr u its listed, h owever, in clu de da ta fr om oth er sou r ces for on e or m or e of th e m in er a ls. For in sta n ce, th e en tr y for cook in g a pples m a k es u se of da ta fr om th e LGC for P, Fe, Cu a n d Zn . Th e va lu es for N a , K, Ca , Mg a r e a n aver a ge of LGC da ta a n d th e old Ch em ica l Com position of food s da ta fr om 1936. Ta ble I lists sou r ces of da ta for a ll th e twen ty ve geta bles a n d fr u its th a t wer e selected for th e com pa r ison . In th is pa per I h ave exa m in ed on ly r aw fr u its a n d ve geta bles. Th is h a s been don e to exclu de differ en ces ca u sed by ch a n ges in m eth ods of pr ocessin g. Th e u pda ted a n a lyses pr ovide a n oppor tu n ity to com pa r e th e ch a n ges in pu r ch a sed r aw food over a ppr oxim a tely a 50-yea r per iod. Methods I a n a lysed twen ty ve geta bles a n d fr u its u sin g two ver sion s of th e Com position of Food s ta bles[3,4]. I u sed th e 1960 ver sion for th e old da ta beca u se it w a s ea sily ava ila ble a n d in clu des th e sa m e a n a lyses a s th e fir st a n d secon d edition s. It a lso r epor ts th e r esu lts to on e m or e sign ifica n t digit th a n th e fou r th edition . Th e fr u its a n d ve geta bles selected h a d to m eet th e follow in g cr iter ia : • Th e old da ta h a d been u pda ted for th e fifth edition of th e food ta bles. Som e fr u its h ave a lso been in clu ded wh en old a n d n ew da ta wer e aver a ged a s ou tlin ed in Ta ble I. • Th e descr iption s of th e a n a lysed por tion of th e food wer e iden tica l. For exa m ple, both sa m ples wer e peeled. • On ly r aw sa m ples wer e in clu ded. • Th e food w a s n ot dr ied or r eh ydr a ted a n d dr y pu lses wer e n ot in clu ded. • Th e food w a s n ot a con dim en t (e.g. h or ser a dish r oot). [ 207 ] Anne-Marie Mayer Historical changes in the mineral content of fruits and vegetables Table I Sources of data for The Composition of Foods tables Fruits Sources and dates of data British Food Journal 99/ 6 [1997] 207–211 Apricots Bananas Blackberries Cherries Cooking apples Eating apples Grapefruit Grapes Lemons Melon cantaloupe Nectarines Oranges Passion fruit Peaches Pears Pineapple Plums Raspberries Rhubarb Strawberries LGC 85-86 except Na: average of literature LGC 85-86 except K, Zn: average of literature LGC 85-86 LGC 85-86 LGC 85-86 except Na, K, Ca, Mg: average of LGC, MW4 LGC 85-86 except Na, K, Cu: average of literature LGC 85-86 except Na, K, Ca: average MW4, USDA 86, literature LGC 85-86 except Na, K, Zn: average of literature MW4, USDA, literature. LGC 85-86 LGC 85-86 except K, Mg: literature LGC 85-86 except K: literature Literature sources LGC 85-86 except K: literature LGC 90 LGC 85-86, MW4, literature Recalculated from stewed plums LGC 85-86 Average of USDA 81, MW4 LGC 85-86 Notes: LGC Laboratory of the Government Chemist MW4 McCance and Widdowson’s Composition of Foods 4th edition (1936 data)[6] USDA United States Department of Agriculture data First to third editions: The data used in the first four editions of the Chemical Composition of Foods were compiled from the 1936 data[2] Fourth edition: The data were compiled from the 1936 data with a few additions from the literature. For example Zn values were added from literature sources Fifth edition: The data for vegetables in the fifth edition were all taken from the Institute of Food Research between 1984 and 1987. The data for fruits were obtained from mixed sources wh eth er ea ch m ea n r a tio w a s sign ifica n tly differ en t fr om 1. Th e logs of th e r a tios wer e u sed for th is test. A tota l of 20 fr u its a n d 20 ve geta bles sa tisfied th ese cr iter ia a n d th ese a r e listed w ith th eir m in er a l con ten ts a t both tim e poin ts in Ta ble III. I ca lcu la ted th e loga r ith m of th e r a tios (n ew :old) for ea ch m in er a l for ea ch fr u it a n d ve geta ble a n d fr om th ese com pu ted th e geom etr ic m ea n s. Stu den ts t-test w a s u sed to test Findings Th e aver a ge r a tios a n d r esu lts of th e t -test a r e listed in Ta ble II. A r a tio of 0.81 for Table II Average a ratio of mineral content (new:old) of 20 vegetables and 20 fruitsb Ca Mg Fe Cu Na K P Dry matter H2O Vegetables ratio 0.81 0.65 0.78 0.19 0.57 0.86 0.94 0.97 1.00 p valuec 0.014* 0.000* 0.088 0.000** 0.013* 0.090 0.487 0.53 0.872 Fruits ratio 1.00 0.89 0.68 0.64 0.90 0.80 0.99 0.91 1.02 p value 0.957 0.016* 0.002** 0.006** 0.561 0.000** 0.903 0.023* 0.006** Notes: a Geometric mean, the antilogarithm of the mean of the logarithm of the ratio of 1980s to 1930s values b See text for data sources and Table III for vegetables and fruits included. Analyses of Mn, Se and I were only added in the 1991 edition. Zn was only added in the 1978 edition. S was omitted from the 1991 tables although it was analysed in previous editions. C1 was not revised in many cases for the 1991 edition. For these reasons comparisons were only possible for the above 7 minerals, water and dry matter. c Probability that average of logarithm of new:old is statistically different from 0 by t-test. (This is equivalent to the ratios being different from 1) * = significant at the 5 per cent level ** = significant at the 2 per cent level [ 208 ] Anne-Marie Mayer Historical changes in the mineral content of fruits and vegetables British Food Journal 99/ 6 [1997] 207–211 ca lciu m , for exa m ple, m ea n s th a t over a n a ppr oxim a te 50-yea r per iod th e aver a ge con ten t of ca lciu m in ve geta bles h a s declin ed to 81 per cen t of th e or igin a l level. Th er e wer e sign ifica n t r edu ction s in th e levels of Ca , Mg, Cu a n d N a , in ve geta bles a n d Mg, Fe, Cu a n d K in fr u its. Th e gr ea test ch a n ge w a s th e r edu ction of copper levels in ve geta bles to less th a n on e-fi fth of th e old level. Th e on ly m in er a l th a t sh owed n o sign ifica n t differ en ces over th e 50-yea r per iod w a s P. Wa ter in cr ea sed sign ifi ca n tly Table III Mineral content of vegetables and fruit (mg/ 100mg) Ca old Vegetables Beetroot Brussels Sprouts Cabbage – winter Carrots – old Celery Lettuce Mushroom Mustard and cress Onions Parsley Parsnips Peas Potatoes – old Pumpkin Runner beans Radishes Swedes Tomatoes Turnips Watercress Fe old Fe new 24.9 20.0 15.0 11.0 0.37 28.7 26.0 19.6 8.0 0.66 1.0 0.7 72.3 48.0 52.2 25.9 2.9 65.9 31.2 325.0 54.8 15.1 7.7 39.0 33.3 43.7 56.4 13.3 58.8 222.0 Ca new 68.0 25.0 41.0 28.0 6.0 50.0 25.0 200.0 41.0 21.0 5.0 29.0 33.0 19.0 53.0 7.0 48.0 170.0 Mg old 16.8 12.0 9.60 9.7 13.2 27.3 7.6 52.2 22.4 30.2 24.2 8.2 23.0 11.4 10.8 11.0 7.4 17.0 Mg new 6.0 3.0 5.0 6.0 9.0 22.0 4.0 23.0 23.0 34.0 17.0 10.0 19.0 5.0 9.0 7.0 8.0 15.0 Cu old Cu new Na old Na new K old K new P old Dry Dry P Matter Matter H2O% H2O% new old new old new 0.07 0.02 84.0 66.0 303.0 380.0 32.1 51 12.9 0.05 0.02 9.6 6.0 515.0 450.0 78.4 77.0 15.7 1.23 0.6 N 0.02 28.4 3.0 240.0 270.0 64.1 46.0 0.56 0.3 0.08 0.02 95.0 25.0 224.0 170.0 21.0 15.0 0.61 0.4 0.11 0.01 137.0 60.0 278.0 320.0 31.7 21.0 0.73 0.70 0.15 0.01 3.1 3.0 208 220 30.2 28.0 1.03 0.6 0.64 0.72 9.1 5.0 467.0 320.0 136.0 80.0 4.54 1.0 0.12 0.01 19.0 19.0 337.0 110.0 65.5 33.0 0.30 0.30 0.08 0.05 10.2 3.0 137.0 160.0 30.0 30.0 8.00 7.7 0.52 0.03 33.0 33.0 1,080.0760.0 128.0 64.0 0.57 0.6 0.10 0.05 16.5 10.0 342.0 450.0 69.0 74.0 1.88 2.8 0.23 0.05 0.5 1.0 342.0 330.0 104.0 130.0 0.75 0.4 0.15 0.08 6.5 7.0 568.0 360.0 40.3 37.0 0.39 0.4 0.08 0.02 1.3 0.0 309.0 130.0 19.4 19.0 0.74 1.2 0.09 0.02 6.5 0.0 276.0 220.0 25.9 34.0 1.88 0.6 0.13 0.01 59.0 11.0 240.0 240.0 27.1 20.0 0.35 0.1 0.05 0.01 52.2 15.0 136.0 170.0 19.0 40.0 0.43 0.5 0.10 0.01 2.8 9.0 288.0 250.0 21.3 24.0 0.37 0.2 0.07 0.01 58.0 15.0 238.0 280.0 27.5 41.0 1.62 2.2 0.14 0.01 60.0 49.0 314.0 230.0 52.0 52.0 Fruits Apricots 17.2 15.0 12.3 11.0 0.37 0.5 0.12 0.06 N 2.0 320.0 Bananas 6.8 6.0 41.9 34.0 0.41 0.3 0.16 0.10 1.2 1.0 348.0 Blackberries 63.3 41.0 29.5 23.0 0.85 0.7 0.12 0.11 3.7 2.0 208.0 Cherries 15.9 13.0 9.6 10.0 0.38 0.2 0.07 0.07 2.8 1.0 275 Cooking apples 3.6 4.0 2.9 3.0 0.29 0.1 0.09 0.02 21.0 2.0 123.0 Eating apples 3.6 3.0 4.7 3.0 0.29 0.1 0.11 0.02 2.4 3.0 118.0 Grapes 11.7 13.0 5.3 7.0 0.34 0.3 0.09 0.12 1.7 2.0 283.0 Grapefruit 17.1 23.0 10.4 9.0 0.26 0.1 0.06 0.02 1.4 3.0 234.0 Lemons 107.0 85.0 11.6 12.0 0.35 0.5 0.26 0.26 6.0 5.0 163.0 Melon cantaloupe 19.1 20.0 20.1 11.0 0.81 0.3 0.04 0.00 13.5 8.0 319.0 Nectarines 3.9 7.0 12.6 10.0 0.46 0.4 0.06 0.06 9.1 1.0 268.0 Oranges 41.3 47.0 12.9 10.0 0.33 0.1 0.07 0.05 2.9 5.0 197 Passion fruit 15.6 11.0 38.6 29.0 1.12 1.3 0.12 N 28.4 19.0 348.0 Peaches 4.8 7.0 7.9 9.0 0.38 0.4 0.05 0.06 2.7 1.0 259.0 Pears 7.5 11.0 7.2 7.0 0.21 0.2 0.15 0.06 2.3 3.0 128.0 Pineapple 12.2 18.0 16.9 16.0 0.42 0.2 0.08 0.11 1.6 2.0 247.0 Plums 12.4 13.0 7.6 8.0 0.33 0.4 0.10 0.10 1.9 2.0 192.0 Raspberries 40.7 25.0 21.6 19.0 1.21 0.7 0.21 0.10 2.5 3.0 224.0 Rhubarb 103.0 93.0 13.6 13.0 0.40 0.3 0.13 0.07 2.2 3.0 425.0 Strawberries 22.0 16.0 11.7 10.0 0.71 0.4 0.13 0.07 1.5 6.0 161.0 Notes: Old: Composition of Foods 3rd edition (1930s data)[4] New: Composition of Foods 5th edition (1980s data)[3] N: No data available Ca, Mg, Fe, Na, K and P were reported to one fewer significant digits in the 1991 tables. 270.0 400.0 160.0 210 88.0 100.0 210.0 200.0 150.0 210.0 170.0 150 200.0 160.0 150.0 160.0 240.0 170.0 290.0 160.0 21.3 28.1 23.8 16.8 16.2 7.7 19.0 15.6 20.7 30.4 23.9 23.7 54.2 18.5 9.7 7.8 15.4 28.7 21.0 23.0 20.0 28.0 31.0 21.0 7.0 8.0 18.0 20.0 18.0 13.0 22.0 21.0 64.0 22.0 13.0 10.0 23.0 31.0 17.0 24.0 12.9 15.7 87.1 87.1 84.3 84.3 9.4 10.2 6.5 4.8 8.5 7.5 7.2 21.3 17.5 21.5 24.2 5.3 8.4 6.7 8.6 6.6 6.7 8.9 10.3 10.2 4.9 4.9 7.4 4.7 11.0 16.9 20.7 25.4 21.0 5.0 8.8 4.6 8.8 6.9 8.8 7.5 90.6 89.8 93.5 95.2 91.5 92.5 92.8 78.7 82.5 78.5 75.8 94.7 91.6 93.3 91.4 93.4 93.3 91.1 89.7 89.8 95.1 95.1 92.6 95.3 89.0 83.1 79.3 74.6 79.0 95.0 91.2 95.4 91.2 93.1 91.2 92.5 13.4 29.3 18.0 18.5 14.4 15.7 20.0 9.3 14.8 6.4 19.8 13.9 26.7 13.8 16.8 15.7 15.4 16.8 5.8 11.1 12.8 24.9 15.0 17.2 12.3 14.6 18.2 11.0 13.7 7.9 11.1 13.9 25.1 11.1 16.2 13.5 16.1 13.0 5.8 10.5 86.6 70.7 82.0 81.5 85.6 84.3 80.0 90.7 85.2 93.6 80.2 86.1 73.3 86.2 83.2 84.3 84.6 83.2 94.2 88.9 87.2 75.1 85.0 82.8 87.7 85.4 81.8 89.0 86.3 92.1 88.9 86.1 74.9 88.9 83.8 86.5 83.9 87.0 94.2 89.5 [ 209 ] Anne-Marie Mayer Historical changes in the mineral content of fruits and vegetables British Food Journal 99/ 6 [1997] 207–211 a n d dr y m a tter decr ea sed sign ifica n tly in fr u its. What role do the minerals play in human nutrition? Min er a ls a ll h ave sever a l r oles in h u m a n bioch em istr y a n d ph ysiology a n d a ll th e m in er a ls m en tion ed a bove a r e essen tia l in th e diet of h u m a n s. Ma n y a r e co-fa ctor s for differ en t en zym es a n d we a r e depen den t on th em for en er gy efficien cy, fer tility, m en ta l sta bility a n d im m u n ity. Alth ou gh fr u its a n d ve geta bles gen er a lly su pply a sm a ll pr opor tion of tota l m in er a l dieta r y r equ ir em en ts, th e r edu ction s cou ld be im por ta n t to som e gr ou ps so th e ca u ses of th e r edu ction s n eed in vestiga tin g. It is n ot clea r wh a t is ca u sin g th e r edu ction s. Th er e a r e sever a l possibilities a n d th ese a r e ou tlin ed below. Are the reductions anomalies of measurement or sampling? Th e ea r lier a n a lyses of som e m in er a ls m ay h ave been in a ccu r a te com pa r ed to m oder n a n a lytica l m eth ods. E lsie Widdow son , h ow ever, n otes in th e in tr odu ction to T h e Com position of Food s[3] th a t “th ose m eth ods wer e n o less a ccu r a te th a n th e m oder n a u tom a ted on es, bu t th ey took a m u ch lon ger tim e”. If th is is tr u e, we sh ou ld be a ble to r ely on th e con sisten cy of th e a n a lytica l m eth ods. How ever, th er e h a s been m u ch deba te over th is qu estion a n d n o clea r con clu sion h a s been r ea ch ed. Th e m eth ods of sa m plin g fr u it a n d ve geta bles wer e design ed to r efl ect th e u su a l ch oice of foods a t th e tim e of th e r esea r ch . Th er e cou ld be differ en ces in th e m eth ods of sa m plin g. It is n ot possible to com pa r e th e deta ils of th e m eth ods u sed beca u se th e or igin a l da ta a r e n o lon ger ava ila ble. Also, th e u se of m ixed sou r ces of da ta for th e 1991 edition of T h e Com position of Food s[3] is a n u n k n ow n fa ctor a n d possible sou r ce of bia s. It is n ot k n ow n wh eth er th e fir st edition of th e Ch em ica l Com position of Food s[1] u sed sim ila r m eth ods of da ta com pila tion . Food system changes In th e pa st sixty yea r s th e food su pply system h a s ch a n ged con sider a bly. For in sta n ce we n ow ea t m or e “ou t of sea son ” a n d im por ted foods gr ow n on a w ide va r iety of soils fr om m a n y differ en t cou n tr ies. Som e of th e fr u its a n d ve geta bles h ave a lw ays been im por ted bu t m a n y of th ose pr eviou sly gr ow n in th e UK a r e a lso n ow im por ted. Stor a ge a n d r ipen in g system s h ave ch a n ged. Gr een h ou se cr ops a r e “br ou gh t on ” m or e qu ick ly n ow a n d often gr ow n in soil-less m ixes. Cou ld th ese pr a ctices h ave ch a n ged th e com position of fr u its a n d ve geta bles? [ 210 ] Th e va r ieties of pla n ts cu ltiva ted n ow h a s a lso ch a n ged. N ow a days we pr a ctise soph istica ted pla n t br eedin g a n d h ave br ed selectively for qu a lities th a t w ill su it th e dem a n ds of, for exa m ple, h igh yield, post-h a r vest h a n dlin g qu a lities a n d cosm etic a ppea l. Also we select va r ieties th a t w ill r espon d well to th e m eth ods of a gr icu ltu r e cu r r en tly em ployed. Specific br eedin g to en h a n ce n u tr ition a l qu a lity is r a r e. Agricultural practices Du r in g th e ea r ly 1930s a gr icu ltu r a l ch em ica ls wer e h a r dly u sed. Ma n u r e a n d com post wer e th e m a in fer tilizer s u sed. After th e w a r pr a ctices ch a n ged a n d fa r m er s beca m e m or e r elia n t on th e u se of fer tilizer s a n d oth er a gr och em ica ls a s well a s h eavy fa r m m a ch in er y. Agr icu ltu r e wh ich r elies on N P K fer tilizer s a n d pesticides, th a t a dds little or ga n ic m a tter to th e soil a n d th a t a lter n a tes between soil com pa ction a n d plou gh in g, cou ld pr odu ce food depleted in m in er a ls. Th ese pr a ctices a ffect th e str u ctu r e, ch em istr y a n d ecology of th e soil in w ays th a t cou ld a ffect th e ava ila bility of m in er a ls to pla n ts a n d h en ce th e m in er a l con ten t of cr ops. For in sta n ce, m ycor r h iza l fu n gi h ave a sym biotic r ela tion sh ip w ith pla n t r oots in wh ich su ga r s a n d m in er a ls a r e exch a n ged. Th e fu n gi a r e r edu ced by h igh levels of ava ila ble ph osph a te a n d n itr ogen , low pH, w a ter loggin g or excessive dr yn ess[5]. An oth er fa ctor cou ld be th e differ in g levels of con ta m in a tion of cr ops w ith r esidu es of pesticides con ta in in g h igh con cen tr a tion s of m in er a ls – for exa m ple Bor dea u x m ixtu r e con ta in s h igh levels of copper a n d w a s w idely u sed a s a pesticide. In pr in ciple, m oder n a gr icu ltu r e cou ld be r edu cin g th e m in er a l con ten t of fr u it a n d ve geta bles. We n eed to fin d ou t if th is, or a n y of th e oth er expla n a tion s descr ibed a bove, a r e sign ifica n t fa ctor s in pr a ctice. Con sider in g th e m a gn itu de of th e r edu ction s th is m a tter deser ves u r gen t a tten tion . The following questions arise from the findings: • • • • • Ar e th e da ta r elia ble? Is th e a ppa r en t declin e ca u sed by dim in ish ed levels of m in er a ls in th e soil, poor ava ila bility, th e ch oice of cu ltiva r s or oth er ch a n ges in th e food system ? To wh a t exten t is th e declin e in m in er a ls of im por ta n ce to h u m a n n u tr ition ? Ar e oth er cou n tr ies exper ien cin g sim ila r ch a n ges? Ar e th er e sim ila r r edu ction s in oth er cr ops – su ch a s cer ea ls? Anne-Marie Mayer Historical changes in the mineral content of fruits and vegetables British Food Journal 99/ 6 [1997] 207–211 • • • • Ar e oth er m in er a ls of equ a l im por ta n ce to h u m a n n u tr ition , su ch a s Se a n d Cr, a lso r edu ced? Ar e oth er n u tr ien ts – for exa m ple, vita m in s – a lso r edu ced? Ar e som e cu ltiva r s pr odu cin g cr ops th a t a r e lower in m in er a ls th a n oth er s? Does soil con ta m in a tion – pa st or pr esen t – a ffect th e m in er a l con ten t of cr ops? To a n swer th ese qu estion s existin g liter a tu r e n eeds to be r eviewed a n d fu r th er r esea r ch ca r r ied ou t a lon g th e su ggested lin es; • a n a n a lysis of th e effect of th e la test Com position of Food s da ta on u su a l diets; • com pila tion of a da ta ba se of h istor ica l da ta fr om differ en t cou n tr ies, differ en t tim e sca les a n d differ en t cr ops; • deta iled a n d con tr olled stu dies of soils a n d th e effects of m eth ods of a gr icu ltu r e on pla n t n u tr ition a n d cr op m in er a l con ten t; • stu dies of th e m in er a l con ten t of fr u it a n d ve geta bles gr ow n u sin g differ en t cu ltiva r s in com m on u se n ow a n d 60 yea r s a go; • r e gu la r m on itor in g of food com position w ith deta ils on cu ltiva r s, m eth ods of gr ow in g a n d soils. References 1 McCa n ce, R.A. a n d Widdow son , E .M., T h e Ch em ica l Com position of Food s, Medica l Resea r ch Cou n cil Specia l Repor t Ser ies N o. 235, HMSO, Lon don , 1940. 2 McCa n ce, R.A., Widdow son , E .M. a n d Sh a ck leton , L.R.B., T h e N u tr itiv e Va lu e of Fru its, Vegetables a n d N u ts, Medica l Resea r ch Cou n cil Specia l Repor t Ser ies N o. 213, HMSO, Lon don , 1936. 3 Holla n d, B., Welch , A.A., Un w in , I.D., Bu ss, D.H., P a u l, A.A. a n d Sou th ga te, D.A.T., M cCa n ce a n d Wid d ow son’s Com position of Food s fi fth ed ition , Roya l Society of Ch em istr y a n d th e Min istr y of Agr icu ltu r e, F ish er ies a n d Food, HMSO, Lon don , 1991. 4 McCa n ce, R.A. a n d Widdow son , E .M., T h e Com position of Food s th ird ed ition , Medica l Resea r ch Cou n cil Specia l Repor t ser ies N o. 213, HMSO, Lon don , 1960. 5 Killh a m , K., S oil Ecolog y, Ca m br idge Un iver sity P r ess, Ca m br idge, 1994. 6 P a u l, A.A. a n d Sou th ga te, D.A.T., M cCa n ce a n d Wid d ow son’s Com position of Food s fou r th ed ition , Min istr y of Agr icu ltu r e, F ish er ies a n d Food a n d Medica l Resea r ch Cou n cil, HMSO, Lon don , 1978. 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