NHANES Study Flawed?
Research: Energy intake and output are underestimated by subjects, say researchers.
Researchers from the Arnold School of Public Health at the University of South Carolina reported recently in PLOS ONE (2013; 8 , e76632) that 40 years of nutrition information from the National Health and Nutrition Examination Survey—the gold standard database for such information—may be fatally flawed.
The methodology that NHANES uses to collect the data—widely and regularly cited as the most comprehensive compilation of information on child and adult health in the U.S. —is not “physiologically plausible,” according to lead study author and exercise epidemiologist Edward Archer, PhD, in a press release. Archer observed that the results of the research suggest that without valid population-level data, speculations regarding the role of energy in increasing obesity prevalence are without empirical support.
In short, the authors said that it would be nearly impossible to survive on most of the energy intakes—the "calories in" and "calories out"—that participants reported. This misreporting of energy intake varied among participants; it was greatest in obese men and obese women, who underreported their intake by an average of 25% and 41% (716 and 856 calories per day), respectively.
To assess the health and nutritional status of the U.S. population, the survey involved interviews of self-reported food and beverage consumption over 24 hours followed by physical examinations. Conducted by the Centers for Disease Control and Prevention and the U.S. Department of Agriculture, the NHANES is the primary source of data for researchers studying the impact of nutrition and diet on health.
"Throughout its history, the NHANES has failed to provide accurate estimates of the habitual caloric consumption of the U.S. population," Archer said. "Although improvements were made to the NHANES measurement protocol after 1980, there was little improvement to the validity of U.S. nutritional surveillance."
IDEA contributing editor Natalie Digate Muth, MD, MPH, RD, observed that “While this article appears to signal alarm bells that our nutrition research is flawed, the truth is that it is well-known and widely-accepted that self-reported nutrition intake is a gross underestimation. We also know that this is especially the case for obese individuals, exactly as this study (and many before it) reported.”
Muth also says that while it would be helpful if researchers could collect truly valid and accurate nutrition intake information on a population level, logistical and financial issues can make it prohibitive to do so. “As such, in the thinking that some information is better than none, NHANES collects self-reported nutrition information. This information ends up a closer indication of norms of what should be eaten rather than what actually is eaten.”
Her conclusion: “There are continual efforts to try to improve accuracy of the data collected, and this study is another reminder that innovation is needed in making it easier and less expensive to collect truly accurate dietary intake information.”
PHOTOGRAPHY: Joel Kramer
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