Our food is los­ing nu­tri­ents

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ANY MID­DLE-SCHOOLER GROKS THE FUN­DA­MEN­TALS OF PHO­TO­SYN­THE­SIS: Fu­eled by sun­light, plants turn car­bon diox­ide and wa­ter into sugar and oxy­gen, which they use to grow stems, roots, leaves, and other tasty bits. As CO2 lev­els con­tinue to rise—we’re on track to dou­ble pre-In­dus­trial lev­els in

the next few decades—it might sound like we’re in for a veg­e­ta­tional boom. But any green­ery growth spurt will come with a down­side. CO2-charged sprouts con­tain more starches and sug­ars, and fewer min­er­als and pro­teins. You can try to avoid junk food, but our plants are get­ting junkier too. See, plants also re­quire pro­teins in or­der to grow, which they syn­the­size us­ing el­e­ments they draw from the soil, such as ni­tro­gen, phos­pho­rus, and potas­sium. In the course of suck­ing up those molecules, greens also take in nutritious min­er­als like zinc and iron. Plants of­ten ab­sorb more than they need, stor­ing the ex­cess in their cells. Then hu­mans get to eat them. Agronomists, how­ever, have recorded a steady de­cline in some of those min­er­als, pro­teins, and vi­ta­mins for half a cen­tury. For ex­am­ple, USDA data shows that kale from 1999 had 23 per­cent less iron than 1950’s greens did. His­tor­i­cally, sci­en­tists have blamed in­dus­tri­al­ized farm­ing for prac­tices like over­work­ing soil, which strips it of the good stuff. But now the blame is shift­ing to in­clude CO2. In 2002, math­e­ma­ti­cian Irakli Lo­ladze the­o­rized that pho­to­syn­the­sis re­quires fewer pro­teins as CO2 climbs, which means plants ac­quire fewer in­ci­den­tal mi­cronu­tri­ents while suck­ing them up—skew­ing the ra­tio of healthy to un­healthy con­tent. He recorded an 8 per­cent nu­tri­ent drop, on aver­age, in cer­tain kinds of crops, in­clud­ing rice and wheat.

In 2014, Lo­ladze and an­other group of sci­en­tists both pub­lished re­search lend­ing weight to his ear­lier hy­poth­e­sis. The two stud­ies drew upon more than a decade of data from agronomists, who had planted 41 va­ri­eties of six food crops—wheat, maize, sorghum, field peas, soy­beans, and rice—and sur­rounded part of each field with noz­zles blast­ing enough CO2 to warm any green­house. Anal­y­sis of the har­vests showed maize and sorghum fared fine, but rice—a sta­ple for half of hu­man­ity—lost about 3 per­cent of its zinc; that could put hun­dreds of thou­sands, if not mil­lions, of peo­ple at risk of de­fi­ciency, leav­ing them more vul­ner­a­ble to res­pi­ra­tory dis­eases, di­ar­rhea, and malaria. If cur­rent trends con­tinue, global at­mo­spheric CO2 lev­els will match those ex­per­i­ments within the next 50 years. When that hap­pens, re­searchers es­ti­mate that hun­dreds of mil­lions—mostly preg­nant women and chil­dren liv­ing in poverty—could end up short on es­sen­tials such as iron, pro­tein, and, yes, zinc. Plus, there’s a chance these ex­tra-sug­ary plants will con­trib­ute to an uptick in di­a­betes—which is al­ready one of the world’s top killers. Un­less we go cold tur­key on our car­bon habit (not likely!), we’ll need to fo­cus on find­ing even-more-nutritious grain va­ri­eties. Those crops would still suf­fer the con­se­quences of too much CO2, but they might keep our di­ets healthy long enough for us to clean things up.

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