Fat de­par­ture

Can we trust nu­tri­tion science, which has once again flip-flopped on guide­lines for fat and choles­terol?

Down to Earth - - COLUMN -

Fwe have been fed on the re­ceived OR DECADES, wis­dom that fat and choles­terol are bad for health. Th­ese two devils,we were warned,not only in­crease the odds of get­ting obese, but also make us more vul­ner­a­ble to in­fir­mi­ties of the heart.So trust­ing the bof­fin’s word, we zeal­ously put a red flag on red meat, aban­doned the plea­sures of egg-yolk,and reluc­tantly re­signed our­selves to the un­ap­peal­ing low-fat,high-carb for­mula. Well,it turns out we have been had. Fol­low­ing a com­pre­hen­sive re­view of three decades of re­search on the diet-health con­nec­tion,US sci­en­tists have prac­ti­cally ab­solved fat and choles­terol of their sup­posed sins. This Fe­bru­ary, ex­perts ad­vis­ing the com­mit­tee re­spon­si­ble for de­vel­op­ing di­etary guide­lines ad­mit­ted there was “no ap­pre­cia­ble re­la­tion­ship” be­tween di­etary choles­terol and blood choles­terol. A few months ear­lier, they had de­bunked the good­ness of low-fat foods by re­mov­ing the cap on daily in­take of to­tal fat. How­ever, ar­ti­fi­cially pro­duced trans fats found in many pro­cessed foods re­main an of­fender.

While the new guide­lines may be meant for Amer­i­cans, they are no less rel­e­vant for any­one en­tan­gled in the global sci­en­tific-in­dus­trial com­plex. With the grad­ual lib­er­al­i­sa­tion of the In­dian econ­omy since 1991, mil­lions of In­di­ans have been con­sum­ing pro­cessed foods de­signed in the West. Be­sides, as the West is still the hub of cut­ting-edge ba­sic re­search in health and nu­tri­tion, our ideas about the com­plex re­la­tion­ship be­tween food, health and medicine are in­creas­ingly shaped by mod­ern science.

So what went awry? Why did it take sci­en­tists six decades to de­tect an er­ror as grave as this? The tor­tu­ous history of the process that nailed the smok­ing-can­cer link might sug­gest prob­a­ble com­plic­ity be­tween ve­nal sci­en­tists, in­dus­tri­al­ists and politi­cians. How­ever, while food com­pa­nies do lobby, the devil here seems to be the na­ture of ev­i­dence used to link diet and health.

The science of nu­tri­tion is founded on epi­demi­ol­ogy, a kind of study in which re­searchers in­ves­ti­gate how two things might be con­nected, say smok­ing and can­cer, by track­ing large groups of peo­ple over a long pe­riod. The trou­ble is that epi­demi­ol­ogy, no mat­ter how rig­or­ously de­signed, can only tell you whether two things are linked and how strongly.Sci­en­tists call it cor­re­la­tion.What it can’t demon­strate is whether one thing causes the other.This is the fun­da­men­tal prob­lem that plagues con­tro­ver­sies on the im­pact of any ex­ter­nal agent on the hu­man body.

Un­til a decade ago, epi­demi­ol­ogy was the dom­i­nant method of elic­it­ing ev­i­dence in nu­tri­tion science. The re­sult­ing guide­lines were, there­fore, based on mere as­so­ci­a­tions that re­searchers, de­pend­ing on fac­tors, such as flawed sta­tis­ti­cal mod­els, pro­fes­sional ri­valry, and con­flict of in­ter­est, could in­ter­pret as strong or weak. But since peo­ple seek cer­tain­ties and not prob­a­bil­i­ties in or­der to take a de­ci­sion, the guide­lines were ren­dered into vir­tual cer­tain­ties.

Many be­lieve that the new guide­lines are a healthy de­par­ture from the past. They are based on a re­view of ran­domised con­trolled tri­als—the gold stan­dard for demon­strat­ing causal­ity— that in­ves­ti­gated the al­leged links be­tween fat and choles­terol with heart dis­ease. For ex­am­ple, one study found that re­plac­ing fat with car­bo­hy­drates is not even an in­sur­ance against heart ail­ments,let alone death.

It is not easy to flesh out the nu­ances of the com­plex con­ver­sa­tion be­tween diet and health. Even so, it doesn’t some­how seem right to turn peo­ple into guinea pigs in or­der to ver­ify science founded on weak ev­i­dence.As Aaron E Car­roll,paediatrics pro­fes­sor at the In­di­ana Univer­sity School of Medicine, wrote in “That is dis­ap­point­ing not only be­cause it re­duces peo­ple’s faith in science as a whole, but also be­cause it may have cost some peo­ple bet­ter health, or po­ten­tially even their lives.”

Can one trust the new guide­lines? May be more than the ear­lier ones. But given nu­tri­tion science’s flip-flop na­ture, one might be bet­ter off fol­low­ing old grandma’s thumb rule: eat ev­ery­thing,but in mod­er­a­tion.


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