Data Analysis for the 2020 Dietary Guidelines Advisory Committee
Data analysis is one of the three scientific approaches that the 2020 Dietary Guidelines Advisory Committee used to review the current scientific evidence. Data analysis provides insights into current eating habits of the U.S. population and diet-related chronic disease rates in the United States.
Data Analysis for the 2020 Advisory Committee
The 2020 Dietary Advisory Committee used data analysis to address topics and supporting scientific questions from USDA and HHS.
These questions looked at:
- Current dietary patterns and beverage consumption
- Current intakes of food groups and nutrients
- Nutrients of public health concern
- Prevalence of nutrition-related chronic health conditions
- Relationships between eating habits and achieving nutrient and food group recommendations
The Committee, with support from Federal staff, developed a protocol for how each question would be answered using data analysis. The protocol, or plan, included an analytic framework that described the overall scope and the approach used to answer the question, and an analytic plan that detailed the data and subsequent analysis to be considered. The analytic results of each analysis that were used to answer a data analysis question are summarized in the Scientific Report of the 2020 Dietary Guidelines Advisory Committee.
Federal Data Sources
The Committee examined a collection of analyses to inform their deliberations. Key nationally representative, Federal data sources include the National Health and Nutrition Examination Survey (NHANES), the National Health Interview Survey (NHIS) and Surveillance, Epidemiology and End Results (SEER). Each of these key data sources is described below. A complete list of Federal Data Sources used by the 2020 Dietary Guidelines Advisory Committee can be found through this page.
National Health and Nutrition Examination Survey
NHANES is a Federal program of studies designed to assess the health and nutritional status of children and adults in the United States. The nationally representative survey includes both interviews and physical examinations that measure dietary intakes and diet-related chronic disease rates in the U.S. population. It is managed by the National Center for Health Statistics (NCHS) of the Centers for Disease Control and Prevention (CDC).
NHANES data are collected continuously and released in two-year cycles. The most recently available data are from NHANES 2015-2016. In many cases, analysis included data from two cycles of NHANES (2013-2014 and 2015-2016) to ensure an appropriate sample size for subgroup analysis. Dietary intakes of infants and toddlers ages 6 to 12 and 12 to 24 months included NHANES 2007-2016 to achieve a sample size stratified by infants receiving human milk and complementary foods and beverages (CFB) or infants receiving any infant formula and CFB. Sample weights for these analyses were recalibrated.
What We Eat in America (WWEIA), NHANES
The dietary component of NHANES, called WWEIA, is the only nationally representative survey of total food and beverage consumption that captures intakes across life stages on a population level in the United States. The dietary data are collected using the gold standard for dietary assessment: a multiple pass, 24-hour dietary recall.
USDA developed the Automated Multiple-Pass Method 24-hour dietary recall (AMPM), which is conducted by a trained dietary interviewer in the WWEIA portion of NHANES. The AMPM is designed to systematically help participants report their food and beverage intake in great detail while minimizing respondent burden. A standard set of measuring guides is used to help participants report the volume and dimensions of the food items consumed. The AMPM is a research-based, multiple-pass approach designed to enhance complete and accurate food recall using 5 steps that are applied consistently in data collection.
The 5 steps include:
- Quick List - Participant recalls all foods and beverages consumed the day before the interview (midnight to midnight).
- Forgotten Foods - Participant is asked about consumption of foods commonly forgotten during the Quick List step.
- Time and Occasion - Time and eating occasion are collected for each food.
- Detail Cycle - For each food, a detailed description, amount eaten, and additions to the food are collected. Eating occasions and times between eating occasions are reviewed to elicit forgotten foods.
- Final Probe - Information on additional foods not remembered earlier is collected.
Each step is based on a strategy to enhance dietary recall. The initial recall is self-defined by the participant and the subsequent steps help the participant to associate eating occasions with the day’s events. The interviewer asks about frequently forgotten foods and assists in the placement of foods with eating occasions. The repetition provides opportunities for adding detail to each reported food or beverage.
Using NHANES Data to Understand Eating Habits of the U.S. Population
The strengths and challenges of self-report dietary assessment are well-recognized. Self-report dietary data are valuable for providing important information at a population level regarding intakes (and sources) of foods and beverages and to describe dietary patterns and assess diet quality. Established statistical approaches accounting for day-to-day variability and energy adjustment are used to help reduce potential bias in describing dietary intakes at a population level.
The dietary data collected during the AMPM is linked to databases that are used to identify the nutrient values and food group contribution of foods reported by participants. The following databases were integrated into the analyses of dietary data that provides comprehensive insight into eating habits of the U.S. population.
- Nutrients: USDA Food and Nutrient Database for Dietary Studies (FNDDS) is a database that provides the nutrient values for foods and beverages. Data are available on energy and 64 nutrients for nearly 9000 foods and beverages. FNDDS allows the Advisory Committee to examine nutrient intakes from foods and beverages reported by Americans.
- Food-guidance Based Food Groups: USDA Food Pattern Equivalents Database (FPED) converts foods and beverages in the FNDDS to 37 USDA Food Patterns components. The FPED allowed the Advisory Committee to examine food group intakes (e.g. Whole Fruit, Total Vegetables) from foods and beverages reported by participants.
Using NHANES to Assess Physical and Biochemical Indicators of Health
NHANES physical exams and laboratory data are useful components of the broader data we use to understand the U.S. population’s health. Examples of physical exam measurements include measured height, weight, and blood pressure. The laboratory tests allow for ongoing assessment of U.S. population status of blood and urine biochemical indicators of nutrients consumed and other markers with public health relevance.
National Health Interview Survey
NHIS is a survey on health conducted using in-person, confidential household interviews. Like NHANES, this survey is managed by the NCHS within CDC. It provides data on the U.S. civilian noninstitutionalized population for analyzing health trends and tracking progress toward achieving national health objectives.
These data, continuously collected throughout the year, are used to characterize those with various health conditions.
Surveillance, Epidemiology, and End Results
The SEER Program is the authoritative source for cancer statistics in the U.S. population. SEER is supported by the Surveillance Research Program (SRP) in the National Cancer Institute Division of Cancer Control and Population Sciences (DCCPS).
SEER collects and publishes cancer incidence and survival data from population-based cancer registries. These registries routinely collect data on patient demographics, primary tumor site, tumor morphology and stage at diagnosis, first course of treatment, and follow-up for survival status. These data are collected on every cancer case reported from 19 U.S. geographic areas.
The geographic area of data collection are representative of the demographics of the entire U.S. population. This broad coverage allows SEER to account for diverse populations throughout the United States. SEER data can be used to define the rates of diet-related cancers in the U.S. population.
Data Analysis Team
The data analysis team supported the work of the Advisory Committee to answer specific topics and questions. The team, which comprised Federal scientists with advanced degrees in nutrition, statistics, and epidemiology, included scientists from the following Departments and agencies:
United States Department of Agriculture
- Center for Nutrition Policy and Promotion; Food and Nutrition Service; Food, Nutrition, and Consumer Services
- Agricultural Research Service; Research, Education, and Economics
United States Department of Health and Human Services
- Office of Disease Prevention and Health Promotion; Office of the Assistant Secretary for Health
- National Cancer Institute; National Institutes of Health
- National Center for Health Statistics; Centers for Disease Control and Prevention
For More Information
Please view the Scientific Report of the 2020 Dietary Guidelines Advisory Committee and the online-only data analysis supplements to learn more about the Advisory Committee’s work.