Everything We Know About Nutrition May Be Wrong

A new study says 40 years of CDC data connecting food and obesity are fundamentally flawed.

National Journal
Brian Resnick
See more stories about...
Brian Resnick
Oct. 10, 2013, 7:52 a.m.

For 40 years, the Cen­ters for Dis­ease Con­trol and Pre­ven­tion has been ask­ing people what they eat in an at­tempt to un­der­stand the con­nec­tions between what we con­sume and how our bod­ies feel. And for 40 years, they may have been do­ing it wrong.

The lim­it­a­tions of the CDC data “make it ex­ceed­ingly dif­fi­cult to dis­cern tem­por­al pat­terns in cal­or­ic in­take that can be re­lated to changes in pop­u­la­tion rates of obesity.”

That’s the claim in a new study pub­lished in the on­line journ­al PLO­Sone. The re­search­ers probe CDC’s Na­tion­al Health and Nu­tri­tion Ex­am­in­a­tion Sur­vey, which has in­ter­viewed Amer­ic­ans about the foods they eat and their life­styles since 1971. From the sur­vey, we learned things about nu­tri­tion that now seem so fun­da­ment­al — that diet and ex­er­cise choices are linked to body weight, that cho­les­ter­ol is linked to heart dis­ease, and so on.

But here’s the prob­lem, ac­cord­ing to the au­thors: All of that data was com­piled by ask­ing people to re­call what they ate.

“Nu­tri­tion sur­veys fre­quently re­port a range of en­ergy in­takes that are not rep­res­ent­at­ive of the re­spond­ents’ ha­bitu­al in­takes,” the au­thors write. “And es­tim­ates of EI [en­ergy in­take] that are physiolo­gic­ally im­plaus­ible (i.e., in­com­pat­ible with sur­viv­al) have been demon­strated to be wide­spread.” Men and wo­men have been found to un­der­re­port cal­or­ies by between 12 per­cent and 20 per­cent, and are more likely to se­lect­ively un­der­re­port eat­ing the bad stuff, such as fat and sug­ar.

Trans­la­tion: We can’t trust hu­man memory as the source of our nu­tri­tion data, be­cause people can un­der­re­port what they eat to an ab­surd de­gree. Their self-re­ports doc­u­mented amounts of food that could not pos­sibly sup­port their sur­viv­al. “In no sur­vey did at least 50 per­cent of the re­spond­ents re­port plaus­ible EI [en­ergy in­take] val­ues,” the au­thors re­port.

The NHANES sur­vey does con­tain many, many ob­ject­ive meas­ures such as phys­ic­al ex­am­in­a­tions and blood work (for in­stance, it found el­ev­ated levels of lead in Amer­ic­ans’ blood work, which lead to the de­creased use of the met­al in gas­ol­ine and soda cans). But it’s not like the CDC can mon­it­or all a per­son eats. Nor is it really feas­able to do large-scale ex­per­i­ments on nu­tri­tion — that is, sep­ar­ate people in­to con­trol and ex­per­i­ment­al groups, have every­one eat the same ex­act things ex­cept for one vari­able, and then com­pile this data over dec­ades.

Gran­ted, in re­cent years, CDC has re­vised i’ts meth­od­o­logy. Since 2001, it has fol­ded NHANES in­to the “What We Eat in Amer­ica Pro­gram, which re­cords food in­take in a more con­trolled man­ner.

But there’s even reas­on to be­lieve that as time went on, and as the sur­vey raised aware­ness of obesity, people’s an­swers be­came even more skewed. The au­thors ex­plain:

“There is strong evid­ence that the re­port­ing of ‘so­cially un­desir­able’ (e.g., high fat and/or high sug­ar) foods has changed as the pre­val­ence of obesity has in­creased. Ad­di­tion­ally, re­search has demon­strated that in­ter­ven­tions em­phas­iz­ing the im­port­ance of ‘healthy’ be­ha­vi­ors may lead to in­creased mis­re­port­ing as par­ti­cipants al­ter their re­ports to re­flect the ad­op­tion of the ‘health­i­er’ be­ha­vi­ors in­de­pend­ent of ac­tu­al be­ha­vi­or change.”

The sur­vey in­dic­ates that health be­ha­vi­or in­flu­ences re­sponses to fu­ture sur­veys. And that’s bad sci­ence. All in all, the au­thors con­clude that the lim­it­a­tions of the NHANES data “make it ex­ceed­ingly dif­fi­cult to dis­cern tem­por­al pat­terns in cal­or­ic in­take that can be re­lated to changes in pop­u­la­tion rates of obesity.”

It doesn’t mean our nu­tri­tion as­sump­tions are wrong. It just means we haven’t proven them, be­cause our meth­ods have been flawed.

What We're Following See More »
How Many People Protested in Philly Yesterday?
1 hours ago

About 5,500, according to official estimates. "The Monday figures marked a large increase from the protests at the Republican National Convention in Cleveland, where even the largest protests only drew a couple of hundred demonstrators. But it’s a far cry from the 35,000 to 50,000 that Philadelphia city officials initially expected."

NY Times’ Upshot Gives Clinton 68% Chance to Win
1 hours ago

Only a day after FiveThirtyEight's Now Cast gave Donald Trump a 57% chance of winning, the New York Times' Upshot fires back with its own analysis that shows Hillary Clinton with a 68% chance to be the next president. Its model "calculates win probabilities for each state," which incorporate recent polls plus "a state's past election results and national polling." Notably, all of the battleground states that "vote like the country as a whole" either lean toward Clinton or are toss-ups. None lean toward Trump.

Indiana Lt. Gov. Tapped to Run for Pence’s Seat
2 hours ago

On the second ballot, the Indiana Republican Party's Central Committee tapped Lt. Gov. Eric Holcomb as their nominee to succeed Gov. Mike Pence this fall. "Holcomb was a top aide to former Gov. Mitch Daniels and Sen. Dan Coats and a former chairman of the state Republican Party."

Sanders May Officially Nominate Clinton
3 hours ago

"Negotiations are underway to have Bernie Sanders officially nominate Hillary Clinton for president at the Democratic National Convention on Tuesday night, a move that would further signal party unity. According to a source familiar with the talks, the Vermont senator would nominate the presumptive Democratic nominee after the roll call vote."

Sanders to Channel His Movement into Local Races
4 hours ago

Bernie Sanders said he'll begin pivoting his campaign to an organization designed to help candidates at the local level around the country. At a breakfast for the Wisconsin delegation to the DNC this morning, he said the new group will "bring people into the political process around a progressive agenda," as it supports candidates "running for school board, for city council, for state legislature."