Policy, Systems, and Environmental Levers to Improve Diet, Population Health, and Health Equity in the United States

Abstract

Our diets and the foods we eat are inextricably connected to our health and wellbeing. Inequitable access to healthy foods and disparities in the US food system have resulted in marginalized groups experiencing the greatest share of the burden of cardiometabolic diseases and health care costs. To support population nutrition and health, a combination of existing and novel strategies has been proposed. In this dissertation, I showcase three examples including sugary beverage excise taxes, national dietary guidelines, and unconditional cash transfers. I aim to deepen our understanding of these interventions and propose improvements that would advance their utility and impact. In the first study (Chapter 2), we examine the impact of a sugary beverage excise tax in Philadelphia, PA, on beverage advertising and availability after 2 years of implementation. The Philadelphia tax, enacted in 2017, increases the shelf price of sugar-sweetened and artificially-sweetened beverages by $0.015/ounce, and has led to important reductions in consumption and sales. Leveraging a longitudinal difference-in-differences approach, we estimated tax-attributable changes in advertising and availability in the city compared to Baltimore, MD (the control), from 4-months pre-tax to 6-, 12-, and 24-months post-tax in small independent stores. Using zero-inflated Poisson and logistic mixed effects models, we found that sugary beverage advertising increased post-tax in Philadelphia (6-months: +1.04 ads/store [95%CI:0.27, 1.80]; 12-months: +1.54 [0.57, 2.52]; 24-months: +0.91 [0.09, 1.72]) relative to Baltimore, driven by increases in low-income zip-codes. While beverage availability did not change in Philadelphia, it did increase in neighboring county stores not subject to the tax, relative to Baltimore. These increases in advertising might have dampened the tax’s effect on purchasing behaviors particularly in low-income neighborhoods, though estimated effects on sales remained large. In the second study (Chapter 3), we examine the within-child associations between changes in adherence to the Dietary Guidelines for Americans, 2020-2025 via the Healthy Eating Index-2020 (HEI-2020) and concurrent changes to BMI among school-aged children in the Growing Up Today Study. The Growing Up Today Study is a longitudinal cohort with two enrollment cycles in 1996 (n=14,233 at baseline) and 2004 (n=7,898), and we computed HEI-2020 and BMI using a validated food frequency questionnaire and self-reported height/weight. Using adjusted fixed effects regression models stratified by natal sex, we found that a 10-point increase in total HEI-2020 was associated with 0.09 (95%CI: 0.051, 0.121) and 0.04 (0.011, 0.066) kg/m2 decreases in BMI for boys and girls, respectively. Subscores for greens and beans, unsaturated fatty acids, and saturated fatty acids were also inversely associated with BMI change, while 1-point improvements in the dairy component were associated with mean BMI increases of 0.02 kg/m2 (95%CI: 0.005, 0.036) for boys and 0.02 kg/m2 (0.009, 0.03) for girls. Relationships between total HEI-2020 and BMI were stronger for those classified as overweight or obesity and for older age. Future research should refine the HEI scoring algorithm and understand whether associations are consistent in more diverse samples. In the third study (Chapter 4), we examine the effects of unconditional cash transfers on diet during the COVID-19 pandemic as part of an intervention implemented in Chelsea, MA, called Chelsea Eats. Unconditional (i.e. unrestricted) cash transfer programs have gained popularity in recent years for their ability to address poverty, but questions remain surrounding their impacts to dietary intake in higher income countries. Through a weighted lottery, a random subset of households who applied to program were given a benefit of up to $400/month, providing the experimental conditions necessary to estimate the effect of the cash transfer. We leveraged data from individuals who responded to an interviewer-assisted 24-hour recall of diet 3-6 months after implementation, and using linear regression models found that the Chelsea Eats benefits led to increased kilocalorie intake (+152.43 [95%CI:76.61, 228.25]), as well as consumption of vegetables (+0.14 cup eq. [0.04, 0.24]) and unprocessed meats (+0.51 oz [0.13, 0.90]). The intervention had stronger effects for those experiencing very low food security at baseline, where Chelsea Eats benefits led to 252.05 (95%CI: 115.07, 389.03) more kilocalories, 0.23 cup eq. (0.03, 0.43) more vegetables, and 1.02 oz (0.35, 1.70) more unprocessed meats consumed. Policymakers should consider cash transfer type interventions as a means to improve nutrition and diet, especially for populations with limited access to other safety net programs. These studies highlight three different yet timely examples of approaches to improve diet that have garnered traction recently for their reach and potential effectiveness. Ultimately, regardless of strategy, the collective efforts of researchers, policymakers, and communities will be needed to sustainably address inequities in the food environment and advance population health.