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Supermarkets: Components of Causality for Healthy Diets—Reply

Supermarkets: Components of Causality for Healthy Diets—Reply In reply Like Lehmann et al, our goal is to improve diets of low-income individuals, particularly those residing in dense urban and sparsely populated rural areas. The ultimate question is how to best achieve this goal. Two other pieces of evidence bolster our reservations about the focus on supermarket access, without consideration of other driving factors. First, a natural experiment in the United Kingdom compared diet behavior before and after introduction of a supermarket in a food desert.1 Compared with a control community, no significant increases in fruit and vegetable consumption occurred. Second, a joint Institute of Medicine–National Academy of Sciences task force workshop (chaired by B.M.P.) on the public health impact of food deserts found limited evidence that placing supermarkets in food deserts alone would improve the diets of poor individuals.2 It is possible that providing supermarkets in isolation of other efforts may not change consumer behavior or improve health. Lehmann et al question the use of fixed-effects modeling, noting that results with this model are less likely to be statistically significant. This is correct because fixed-effects methods result in larger coefficient standard errors. However, in the presence of unmeasured confounding, it is well known that the tighter confidence intervals achieved by random-effects models could yield biased, highly misleading results. Fixed-effects modeling eliminates time-constant unmeasured confounders and corrects for this source of bias. This approach is widely used in many disciplines despite the cost in lost degrees of freedom. Furthermore, our formal testing (Hausman-Taylor) indicated that fixed effects were warranted in our analyses, thus we reported the more robust fixed-effects findings. Researchers and policy makers from around the United States are working together on multifaceted approaches to improve diets of individuals living in food deserts, incorporating cooking lessons, vegetable subsidies, and other components. Furthermore, foods are increasingly purchased in a wide variety of settings outside of grocery stores and supermarkets. In particular, recent approaches such as the Healthy Corner Store Initiative3,4 has helped to shift the focus toward availability of healthy foods in settings other than supermarkets, as has recent partnerships with Walgreens to offer healthier, affordable food in drug stores across rural and urban landscapes.5 Lehman et al are correct in that no single study should shape today's public health policies. But policies must recognize and address the complexity of diet behaviors and the vast array of barriers facing low-income households and communities. Back to top Article Information Correspondence: Dr Gordon-Larsen, Department of Nutrition, University of North Carolina, 123 W Franklin St, University Square, Chapel Hill, NC 27516 (pglarsen@unc.edu). Financial Disclosure: None reported. References 1. Cummins S, Petticrew M, Sparks L, Findlay A. Large scale food retail interventions and diet. BMJ. 2005;330(7493):683-68415790619PubMedGoogle ScholarCrossref 2. Tarnapol Whitacre P, Tsai P, Mulligan J. The Public Health Effects of Food Deserts: Workshop Summary. Washington, DC: Institute of Medicine and National Research Council; 2009 3. Borradaile KE, Sherman S, Vander Veur SS, et al. Snacking in children: the role of urban corner stores. Pediatrics. 2009;124(5):1293-129819822591PubMedGoogle ScholarCrossref 4. Lucan SC, Karpyn A, Sherman S. Storing empty calories and chronic disease risk: snack-food products, nutritive content, and manufacturers in Philadelphia corner stores. J Urban Health. 2010;87(3):394-40920405225PubMedGoogle ScholarCrossref 5. The White House, Office of the First Lady. First Lady Michelle Obama announces nationwide commitments to provide millions of people access to healthy, affordable food in underserved communities. http://www.whitehouse.gov/the-press-office/2011/07/20/first-lady-michelle-obama-announces-nationwide-commitments-provide-milli. Accessed October 12, 2011 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Internal Medicine American Medical Association

Supermarkets: Components of Causality for Healthy Diets—Reply

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Publisher
American Medical Association
Copyright
Copyright © 2012 American Medical Association. All Rights Reserved.
ISSN
0003-9926
eISSN
1538-3679
DOI
10.1001/archinte.172.2.196
Publisher site
See Article on Publisher Site

Abstract

In reply Like Lehmann et al, our goal is to improve diets of low-income individuals, particularly those residing in dense urban and sparsely populated rural areas. The ultimate question is how to best achieve this goal. Two other pieces of evidence bolster our reservations about the focus on supermarket access, without consideration of other driving factors. First, a natural experiment in the United Kingdom compared diet behavior before and after introduction of a supermarket in a food desert.1 Compared with a control community, no significant increases in fruit and vegetable consumption occurred. Second, a joint Institute of Medicine–National Academy of Sciences task force workshop (chaired by B.M.P.) on the public health impact of food deserts found limited evidence that placing supermarkets in food deserts alone would improve the diets of poor individuals.2 It is possible that providing supermarkets in isolation of other efforts may not change consumer behavior or improve health. Lehmann et al question the use of fixed-effects modeling, noting that results with this model are less likely to be statistically significant. This is correct because fixed-effects methods result in larger coefficient standard errors. However, in the presence of unmeasured confounding, it is well known that the tighter confidence intervals achieved by random-effects models could yield biased, highly misleading results. Fixed-effects modeling eliminates time-constant unmeasured confounders and corrects for this source of bias. This approach is widely used in many disciplines despite the cost in lost degrees of freedom. Furthermore, our formal testing (Hausman-Taylor) indicated that fixed effects were warranted in our analyses, thus we reported the more robust fixed-effects findings. Researchers and policy makers from around the United States are working together on multifaceted approaches to improve diets of individuals living in food deserts, incorporating cooking lessons, vegetable subsidies, and other components. Furthermore, foods are increasingly purchased in a wide variety of settings outside of grocery stores and supermarkets. In particular, recent approaches such as the Healthy Corner Store Initiative3,4 has helped to shift the focus toward availability of healthy foods in settings other than supermarkets, as has recent partnerships with Walgreens to offer healthier, affordable food in drug stores across rural and urban landscapes.5 Lehman et al are correct in that no single study should shape today's public health policies. But policies must recognize and address the complexity of diet behaviors and the vast array of barriers facing low-income households and communities. Back to top Article Information Correspondence: Dr Gordon-Larsen, Department of Nutrition, University of North Carolina, 123 W Franklin St, University Square, Chapel Hill, NC 27516 (pglarsen@unc.edu). Financial Disclosure: None reported. References 1. Cummins S, Petticrew M, Sparks L, Findlay A. Large scale food retail interventions and diet. BMJ. 2005;330(7493):683-68415790619PubMedGoogle ScholarCrossref 2. Tarnapol Whitacre P, Tsai P, Mulligan J. The Public Health Effects of Food Deserts: Workshop Summary. Washington, DC: Institute of Medicine and National Research Council; 2009 3. Borradaile KE, Sherman S, Vander Veur SS, et al. Snacking in children: the role of urban corner stores. Pediatrics. 2009;124(5):1293-129819822591PubMedGoogle ScholarCrossref 4. Lucan SC, Karpyn A, Sherman S. Storing empty calories and chronic disease risk: snack-food products, nutritive content, and manufacturers in Philadelphia corner stores. J Urban Health. 2010;87(3):394-40920405225PubMedGoogle ScholarCrossref 5. The White House, Office of the First Lady. First Lady Michelle Obama announces nationwide commitments to provide millions of people access to healthy, affordable food in underserved communities. http://www.whitehouse.gov/the-press-office/2011/07/20/first-lady-michelle-obama-announces-nationwide-commitments-provide-milli. Accessed October 12, 2011

Journal

Archives of Internal MedicineAmerican Medical Association

Published: Jan 23, 2012

Keywords: diet

References