Background

Cancer is the second leading cause of death overall, behind heart disease, in the US, while it is third among Veterans, behind accidents and suicide per CDC and VA data.   Risk factors for cancer include nonmodifiable factors like age, sex, and genetics, as well as modifiable factors such as alcohol consumption, tobacco use, physical activity, and dietary patterns. Obesity and being overweight due to lack of exercise and an unhealthy diet have been linked to 13 types of cancer by the International Agency for Research on Cancer, accounting for 40% of all US cancer diagnoses annually. These cancer types include endometrial, esophageal adenocarcinoma, gastric cardia, liver, kidney, multiple myeloma, meningioma, pancreatic, colorectal, gallbladder, breast, ovarian, and thyroid cancers. The mechanisms linking obesity to cancer risk involves chronic inflammation, hormonal disturbances, and changes in the gut microbiome. The heightened chronic inflammatory state resulting from obesity may also increase the risk of cancer mortality.

Food Deserts and Food Swamps

Within the past 10 years or so, there have been new barriers found and described which may limit someone’s ability to live a healthier lifestyle.   One is food deserts, which the authors here define as:  geographic regions where low-income persons live more than a mile away from a supermarket and lack healthy food options in an urban area, or more than 10 miles away in a rural area.    Food swamps by contrast have increased availability to proinflammatory, highly processed foods when compared to fresh food options or no options.  Food deserts and food swamps are most concentrated in the Southern and Southeastern regions of the county, where there are similar clusters of breast, lung, colorectal, and prostate cancers.

Research Question, Methods, and Results:

The authors objective to the study:   What are the odds of high obesity-related cancer mortality rates in US counties with low-income food desert or food swamp environments?

Research methods and design:

• Cross-sectional study using data from 3038 US counties; for 2012, 2014, 2015, 2017, and 2020
• 7% of all US counties included
• County-level cancer mortality data for multiple cancer diagnoses according to Centers for Disease Control, >18 yrs old, non-institutionalized
• County-level food environment data from Economic Research Service of USDA (ers.usda.gov/data-products/food-environment-atlas/go-to-the-atlas)
• Primary Outcome: obesity-related cancer mortality
• Variables:
  • food deserts = proportion of each county’s population having both low-income and low access to grocery stores
  • Food swamp score = ratio of fast-food restaurants and convenience stores to grocery stores, farmer’s markets; modified from the RFEI (Retail Food Environment Index) score.
    • Scores for deserts and swamps converted to low, moderate, and high scores.
    • Higher scores (20 to >58) = counties with few healthy food resources
  • Other variables: % race, ethnicity, age, median household income, poverty rate, adult obesity rates per county

Both food desert and food swamp scores were positively correlated with obesity-related cancer mortality.

The age-adjusted odds of counties having high obesity-related cancer mortality were elevated by 77% among counties with high food swamp scores.  This level of association was higher than that of food deserts and cancer outcomes.

After adjusting for age, race, and poverty rate, there was an almost 30% increased odds of high obesity-related cancer mortality among counties with high food swamp scores.  However, after adjusting for adult obesity rates, there was no significant association between high or moderate food swamp scores and high obesity-related cancer mortality.  Also, when the authors fully adjusted models between tertiles of the food environment measures and obesity-related cancer mortality, no significant associations were found.

Conclusions and Future Considerations

Despite reduced cancer mortality rates in the US, previous studies have shown that socioeconomic factors and social determinants of health can impact cancer outcomes.  This study found that counties with higher food swamp scores had a 77% elevated risk of obesity-related cancer death, and a more than 2-fold increased risk of cancer mortality compared to counties with moderate or low food swamp scores. This suggests that food swamps, areas with few healthy food resources, may be a more comprehensive indicator of the US food environment compared to food deserts. Previous studies have also found associations between food environments and obesity-related cancers, with one study showing a 16% mortality risk for breast cancer patients and a 12% greater mortality risk for colorectal cancer patients in food deserts.

Understanding the link between residing in a food desert or food swamp and the potential impact on obesity-related cancer outcomes, particularly among different racial and ethnic groups, warrants further investigation. Future prospective studies have the potential to shed light on the relationships between the historical context of redlining (denial of services based on socioeconomic status, racial or minority group), disparities in food access, and health outcomes, providing valuable insights into the intersections of social and environmental determinants of health.

It is reasonable that food swamps may increase cancer risk as it means having more proinflammatory food choices, such as refined carbohydrates, sugar-sweetened beverages, and highly processed meats.

The strength of the analysis lies in its leveraging complete data on most US counties and employing a comprehensive novel scoring system to differentiate between food deserts and food swamps, which enhances the robustness of the findings. This study marks a significant step in shedding light on the adverse effects of food swamps on health outcomes in the US and highlights the urgency of addressing the systemic issues contributing to the proliferation of food swamps.

There are some limitations to consider for this study.   While providing valuable insights at the county level, the methodology does not establish causal associations between food environments and obesity-related cancer mortality. Future research incorporating temporal sequences and individual-level data can provide a deeper understanding of these associations. Additionally, the reliance on county-level data for race, ethnicity, and income limits the ability to examine potential racial, ethnic, and socioeconomic differences at the individual level in the context of food deserts and food swamps.   Moreover, the validity of what was reported by counties as “healthy food resources” could be questionable; what defines a grocery store?   Tobacco use was unknown in the data, and so may have contributed to cancer risk as there are at least six cancer types which are with tobacco use and overweight/obesity.   Tobacco use tends to be higher among lower socioeconomic communities.

Community gardens can serve as a promising resource to address the challenges posed by unhealthy food environments in the US. By fostering local community engagement and providing opportunities for individuals to grow and access fresh, nutritious produce, community gardens can contribute to improving food access and promoting healthier eating habits. Moreover, community gardens also offer the potential to increase physical activity and provide a space for social interaction, thereby addressing multiple aspects of a healthy lifestyle.

In conclusion, this study underscores the potential impact of food deserts and food swamps on obesity-related cancer mortality in the US. The emergence of food swamps as a growing epidemic necessitates urgent attention and concerted efforts from local and state authorities.  Moving forward, there is a critical need for further research that delves into the mediating associations of obesity and social determinants of health with unhealthy food environments, leveraging both group-level and individual-level data.  Prospective studies and interventions should prioritize the exploration of preventive strategies that integrate community gardens to improve healthy food access, particularly in areas affected by food deserts and food swamps.

Resource

Food Environment Atlas:   Food environment factors—such as store/restaurant proximity, food prices, food and nutrition assistance programs, and community characteristics—interact to influence food choices and diet quality.

https://www.ers.usda.gov/data-products/food-environment-atlas.aspx

Article Review by: 
Matthew Grant, MS, RD, LDN
Dietitian
Durham VA Health Care System