What is the NHANES?
The NHANES is a series of reports or studies that was funded by the CDC (Centers for Diseases Control and Prevention), that was designed to assess the health and nutrition status of American children and adults. It involved interviews and physical examinations over specific spans of time. Some of the data was collected over several years, and some specific studies were shorter in duration. The first NHANES (NHES I) was done from 1960-1962, the second NHES II was done from 1963 to 1965 and the NHES III was done from 1966-1970. NHES I focused on chronic diseases and individuals ages 18-79; NHES II included kids ages 6-11, while NHES III focused on teens ages 12-17. All three had a sample size of about 7500 participants.
NHANES I, II and III took place between the years 1971 and 1994, and are referenced often. There was a separate NHANES that looked at Hispanic health, and a longer term NHANES, which has continued from 1994 through present.
Were there issues with these surveys?
One of the biggest problems with these data sets was the fact that many ethnic subsets of the population were not included or evaluated. Of course, any “survey” is only as good as the recall of the participant, since many of the questions rely on a person’s ability to remember past eating habits and other lifestyle data. In the NHANES III, there was a 30% participation by black Americans and Mexican Americans, in a pool of about 40,000 individuals.
Was the data considered reliable?
Up until recently, these studies were used as the gold standard for extrapolating information that related to government health recommendations, especially in the nutrition sector. Private sector companies drew upon NHANES studies to devise vitamin recommendations, dietary recommendations, and other health-habit suggestions. Recently, researchers from the Arnold School of Public Health at the University of South Carolina called the data “flawed” because of the methods used to collect the information. Specifically, the researchers called into question the “significant limitations in the measurement protocols” used in the NHANES. A PLOS ONE journal report revealed that a “majority of the nutrition data are not physiologically credible.”
At issue is the self-reported recall of food and beverage consumption by survey participants, which was then correlated to their height, weight, age and sex, and then used to predict energy expenditure. In simpler terms, if you say you ate a certain amount of food and then engaged in a specific amount of exercise (per your recall), and your recall is faulty, then conclusions made about weight loss, weight gain or weight maintenance are going to be faulty too. In fact, if you look at “calories in” and “calories out,” as reported by the individuals, most are “physiologically implausible” and not consistent with basic survival. We humans tend to underestimate what we eat, or simply forget everything we consumed in a day, and over estimate our fitness efforts.
Side note: As a nutritionist I consistently find that clients under report calories consumed and over-report their exercise minutes and intensity of effort. So I have always been skeptical of NHANES data. It’s human nature to “fudge information” and we mostly err on the side of “eating less and exercising more,” when we discuss our personal lifestyle habits.
Why is the lapse in accurate data collection so crucial to the data findings?
Many researchers used the data to make conclusions about trends in caloric consumption and determined public policy for diet and health recommendations. If the data is wrong or flawed, then the recommendations based on that data may also be seriously flawed or simply not realistic or fully relevant. Tens of millions of dollars were spent on the NHES and NHANES studies and more money has been assigned to further data surveys. If the methods are flawed then we need to re-think methodology and how funds are assigned to these large studies.
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Amy Hendel is a health professional, journalist and host of Food Rescue, Simple Smoothies and What’s for Lunch? Author of Fat Families, Thin Families and The 4 Habits of Healthy Families, she tweets health headlines daily @HealthGal1103. Catch her guest appearances on Marie! on Hallmark and other local and national news and talk shows.
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Published On: October 17, 2013