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 »
“In the spring of 1971, I met a girl,” started Bill Clinton. In his speech Tuesday night at the Democratic National Convention, Clinton brought a personal touch, telling parallel stories of his relationship with Hillary Clinton and the work she has done throughout her career. He lauded the Democratic nominee for her career of work, touching on her earliest days of advocacy for children and those with disabilities while in law school, her role as Secretary of State, and her work in raising their daughter, Chelsea. Providing a number of anecdotes throughout the speech, Clinton built to a crescendo, imploring the audience to support his wife for president. "You should elect her, she'll never quit when the going gets tough," he said. "Your children and grandchildren will be grateful."
A coalition of mothers whose children lost their lives in high profile cases across the country, known as the Mothers Of The Movement, were greeted with deafening chants of "Black Lives Matter" before telling their stories. The mothers of Sandra Bland, Jordan Davis, and Trayvon Martin spoke for the group, soliciting both tears and applause from the crowd. "Hillary Clinton has the compassion and understanding to comfort a grieving mother," said Sybrina Fulton, the mother of Trayvon Martin. "And that's why, in the memory of our children, we are imploring you — all of you — to vote this election day."
With the South Dakota delegation announcing its delegate count, Hillary Rodham Clinton is officially the Democratic nominee for president, surpassing the 2383 delegates needed to clinch the nomination. Clinton is expected to speak at the convention on Thursday night and officially accept the nomination.
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."
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.