Nutritional surveillance data in the United States obtained via the National Health and Nutrition Examination Survey (NHANES) over the past 39 years are of little use for the development of public policy and dietary guidelines. These are the conclusions of a new study published online October 9 in PLoS One.
The main criticism of the study, led by Edward Archer, PhD, from the Arnold School of Public Health, University of South Carolina, Columbia, is the use of self-reported data for energy intake in NHANES, which the authors say does not accurately reflect calorie consumption for the majority of Americans.
Dr. Archer told Medscape Medical News, "90% of the federal government budget for nutrition and obesity research is spent on self-reported energy intake, the 24-hour recalls, which have been demonstrated to be invalid for 20 years...NHANES is using a tool that is so inaccurate and so invalid, with the result that everything we say we know about diet is invalid, because it's based on 40 years of pseudoscience."
One of the unfortunate consequences of this, he added, is that almost all federal funding is being spent trying to find ways to reduce energy intake, "while almost no money is being spent on calories out," such as looking at ways to encourage people to exercise.
Dr. Archer contends that instead of trying to assess energy intake, a much better way to approach this would be to measure energy expenditure and storage, allowing more accurate calculations of weight change. Use of such measurements would generate much more realistic estimates for federal planning, he said.
Asked to comment on these findings for Medscape Medical News, Walter C. Willett, MD, DrPH, chair of the department of nutrition at the Harvard School of Public Health, Boston, Massachusetts, said the concept that self-reported energy intake is generally underreported is nothing new. While he acknowledges that the NHANES data are imperfect, he believes that they still have a role to play. And he disagrees with Dr. Archer that studying energy expenditure is the way to go; he believes measuring adiposity would be the better choice.
Reported Calorie Consumption Would Not Be Sustainable
In their paper, Dr. Archer and colleagues performed a novel evaluation of NHANES data collected between 1971 and 2010, which encompassed 9 survey periods. They determined the validity of the figures generated using self-reported food intake by calculating the ratio of reported energy intake (rEI) to estimated basal metabolic rate (BMR), and subtracting estimated total energy expenditure (TEE) from NHANES rEI. The TEE data used were based on predictive equations from the Institute of Medicine (IOM).
The researchers found that the historical rEI/BMR values for the majority of the population (67.3% of women and 58.7% of men) were 1.31 and 1.19, respectively. Previous studies have shown that rEI/BMR values <1.35 are physiologically implausible "and reflect underreporting of calorific intake by the NHANES surveys," they say.
For example, they estimate that mean caloric consumption was underreported by 716 kcal/day and 856 kcal/day among obese men and women, respectively, over the periods surveyed. Dr. Archer said that underreporting of calorific intake is the norm, but in a small minority of people there is overreporting.
"We are using subjective data (self-reported dietary-energy intake) — the same methodology developed in the 1950s — to determine public policy" in the 21st century, said Dr. Archer.
He also noted that changes to successive surveys "are constantly muddying the waters." For example, recent NHANES data claim that calorie consumption is going down, yet obesity continues to rise, he observed.
"But this is simply because public-health messages about eating less are starting to work, and these tell people how to lie, they tell people how to fill in the surveys."
Survey Data Imperfect but Still Valuable; BMI Would Be Most Helpful
Dr. Willett acknowledged that "From many studies we know that energy intake is underreported, including the 24-hour recall method used in NHANES…and thus for individuals does not represent their usual diet well."
That said, "We have many indications that the NHANES data can provide useful information, especially for examining trends over time and comparisons of group averages," he observed.
"And even if we had perfect information on energy intake, it would be hard to interpret without similarly precise measures of physical activity, and we certainly don't have that," he added in an e-mail to Medscape Medical News.
But he doesn't think energy-expenditure studies are the answer, either. They "are really not that helpful…because they can't tell us whether a person or population is overconsuming or just physically active."
Rather, "measures of adiposity such as body mass index [BMI] are really most helpful, because they very precisely reflect the balance between input and physical activity," Dr. Willett contended.
Funding for this study was provided by the Coca-Cola Company. Dr. Archer has disclosed no relevant financial relationships. Disclosures for the coauthors are listed in the article. Dr. Willett has disclosed no relevant financial relationships.
PLOS ONE . Published online October 9, 2013. Article
Medscape Medical News © 2013
Cite this: NHANES Diet Data: 'Pseudoscience' Informs US Policy - Medscape - Oct 16, 2013.