Case study based on: Ng, S.W., Slining, M.M., Popkin, B. (2014). Turning point for US diets? Recessionary effects or behavioral shifts in foods purchased and consumed. American Journal of Clinical Nutrition.
In the United States, mean energy consumption has been declining since 2003-2004 (Ford et al., 2013), and obesity prevalence based on data through 2014 also stagnated for children and adults (Ogden et al., 2016; Flegal et al., 2012). Though the most recent sectional National Health and Nutrition Examination Survey (NHANES) of 2015/16 suggested that obesity prevalence has begun to increase again (Hales et al., 2017), the reasons for this plateau in the 2000’s through 2014 are uncertain. Ng et al. (2014) posited that the Great Recession that took place between late 2007 and mid 2009 as well as other adverse economic events that influenced food prices could have been contributing factors to the slowing trend.
This case study, based on the work by Ng et al. (2014), highlights the novel use of nationally representative 24-hour Dietary Recall (24HR) data combined with longitudinal household food purchase data to assess the relationship between adverse economic conditions and reductions in energy intake in the first decade of the 21st century. The following paragraphs summarize the methods and findings from Ng et al. (2014) and the strengths and weaknesses of using 24HR and household expenditure data to try to understand the influence of economic events on food consumption and purchases in the past decade.
The authors worked with 24HR collected as part of the cross-sectional NHANES in 2003-2004, 2005-2006, 2007-2008 and 2009-2010 to analyze diet trends in children and adults. Since 2002, NHANES has collected 2 days of dietary intake data in each survey round, but the authors used just the first day for their analyses. Food data were matched with nutrient information from the USDA Food Composition Table (FCT) to then calculate mean daily energy intakes. Total individual energy intake was expressed in kcal/day and classified by source (store, away from home, or other). Longitudinal household purchase data were obtained from the Nielsen Homescan, a commercial data set with information on products with barcodes that households purchase per shopping episode. These data provided detailed information about packaged foods and beverages purchased including the total amount paid for each product and household characteristics. The authors combined the purchase data with Nutrition Facts Panel data from multiple sources including the Mintel Global New Product Database to impute the caloric content of each product. Lastly, the authors used average monthly unemployment rates as a proxy for the economic landscape in local economies surrounding households in the Homescan database to then analyze the contribution of economic recession effects on trends in food consumption and purchase.
The authors found a significant decline in average daily individual energy intake between 2003-2004 and 2009-2010 for children 2-18 years old for beverages and foods and, for adults >19 years old, the decline was significant for beverages only. The largest statistically significant decrease in total individual energy intake among children occurred in Mexican Americans, children from low-income families and those whose household head had a high school education. Declines in adult total energy intake were smaller, and were significant only among Mexican Americans, women, and adults with some college education. Average daily per capita calories purchased from food and beverages also declined over time for both households with children and households with adults only. Purchase data suggested that reductions in calories purchased from beverages started occurring earlier than for food. The authors’ analyses concluded that these observed changes in food consumption and purchasing behaviors were ultimately independent of the Great Recession or food price changes. They were unable to test other potential causal factors in their models but speculate that the reductions calorie intake reductions may have been due to evolving health consciousness and increased marketing of nutritious alternatives by food manufacturers and retailers. Even though the study offered promising findings in terms of calorie intake, the results do not mean that the overall diet quality of US diets improved. Given that these trends appear to have reverted to increasing overweight and obesity in the ensuing years since the study was conducted, the authors’ call for policies to continue to improve the nutritional quality of food supply, purchase, and eating patterns remain relevant.
This case study is an example of how nationally representative 24HR and purchase data can be combined to assess trends in food consumption and purchase in order to examine their relationship with food prices and general economic recession. The 24HR approach provides quantitative information on individual diets and offers a higher degree of accuracy in assessing food and nutrient intake than Food Frequency Questionnaires or estimates derived from Household Consumption and Expenditure Surveys. Moreover, 24HR questionnaires can include information on food sources and preparation methods that can provide a better understanding of typical household food preparation, cooking methods and brand names of foods consumed. Though, 24HR are complex surveys and require high level of training of enumerators to minimize errors in data collection, the US and many other countries invest in the routine collection of national 24HR data for national nutrition and health surveillance. Like many other types of surveys, 24HR are subject to recall bias since they rely on respondent memory. In order to calculate usual intake from a 24HR survey, it is advised to collect recalls on at least two non-consecutive days for at least a subsample of individuals. The authors of this paper did not implement multiple recalls on the same individuals, limiting the inferences they can draw about the dietary patterns they studied.
The authors took advantage of NHANES’ rich database to analyze dietary intake collected using 24HR to study calorie consumption trends and their relationship with adverse economic conditions in the United States. This type of analysis can help policy makers to better understand how macroeconomic events such as recessions or price shocks may affect dietary shifts and obesity incidence.
- Ford, E.S. & Dietz, W.H. (2013). Trends in energy intake among adults in the United States: findings from NHANES. Am J Clin Nutr, 97:848–53.
- Flegal, K.M., Carroll, M.D., Kit, B.K., & Ogden, C.L. (2012). Prevalence of obesity and trends in the distribution of body mass index among us adults, 1999-2010. JAMA, 307:491–497.
- Hales, C.M., Carroll, M.D., Fryar, C.D., & Ogden, C.L. (2017). Prevalence of obesity among adults and youth: United States, 2015-2016.NCHS Data Brief. No. 288. October 2017.
- Ng, S.W., Slining, M.M., & Popkin, B. (2014). Turning point for US diets? Recessionary effects or behavioral shifts in foods purchased and consumed. Am J Clin Nutr, 99:609-616.
- Ogden, C.L., Carroll, M.D., Lawman, H.G., Fryar, C.D., Kruszon-Moran, D., Kit, B.K., & Flegal, K.M. (2016). Trends in obesity prevalence among children and adolescents in the United States, 1988-1994 through 2013-2014. JAMA, 315(21):2292-2299.