Pablo Monsivais and colleagues reflect on the evidence for interventions to improve access to healthy food, and discuss considerations for evidence-generation
CREDIT: This is an edited version of an article that originally appeared on The BMJ
Improving diet is a key goal of public health, as a substantial fraction of global morbidity and mortality is attributable to dietary imbalances. These imbalances include insufficient consumption of vegetables, fruits and whole grains, and excessive intake of refined carbohydrates and meat. Moreover, inequities in health are driven, in part, by inequities in diet, and tackling them is a key dimension to improving diet and health at the population level.
The past 20 years have seen increasing concern over structural factors that promote unhealthy dietary patterns and undermine the adoption of healthy eating. The general consideration of ‘access to healthy food’ is now a central pillar of policy, systems and environments interventions, as well as so-called ‘whole systems’ approaches to improve nutrition and reduce obesity and chronic disease.
As policy makers and communities act to forge more healthful, sustainable and equitable food systems and environments, researchers recognise the uneven evidence base and debate the importance of economic and geographical factors as population level determinants of diet and health.
What is the evidence to support policy action?
Implicitly or explicitly, considerations of affordability and availability are factored into some approaches to promoting healthy diets; for example, government food assistance and other food subsidy programmes are predicated on improving the affordability of healthy foods, while many policies aiming to create healthy community environments presume that availability is a determinant of food choice and dietary quality.
For more than 125 years home economists and nutrition scientists have recognised the economic dimension of diets – including trade-offs between the nutritive value and cost of foods. Research on food prices, dietary costs and affordability in relation to food choices and dietary quality has been based on highly varied data sources and study designs. Observational studies have examined food prices and affordability, variously defined as the cost of, or expenditure on, (healthier) food relative to income, in relation to diet and health. Generally, healthier foods and diets cost more for consumers, and lower affordability, whether because of higher prices for healthier foods or lower incomes, is linked to the purchase or consumption of less healthy diets and poorer health outcomes. Although fewer studies have considered the time cost associated with healthier diets, research indicates that diets composed of minimally processed, healthy foods can be affordable in terms of ingredients but more costly when the time entailed in preparing meals is accounted for.
Food access research has, typically, defined availability at two scales; at the community scale in terms of the presence, density and variety of supermarkets, grocery stores, or other retail outlets that sell healthier foods at relatively low prices, and at the scale of the within store retail environment, describing the presence, quantity and variety of healthy food options on the shelves.
At either scale, observational studies suggest that limited availability is associated with poor diets, obesity and higher risk of chronic disease, while other studies have not confirmed these associations. Weighing the mixed evidence, systematic reviews have called for more robust methods, preferably based on prospective designs and accounting for mobility patterns and potential selection effects, which haunt many observational studies of built environments and health.
More robust studies on availability within store retail environments have been based on investigator designed interventions. These enhance availability of healthier foods in convenience stores or other retail outlets that, typically, lack healthier options. Although these interventions could lead to beneficial changes in dietary and health outcomes, a limitation has been that they often combine the availability intervention with other intervention components, for example, educational materials or promotions, making it difficult to isolate the effects of individual components.
Understanding the importance of food access in promoting healthy diets will require multiple disciplinary perspectives and approaches. The judicious selection of methods and research designs that acknowledge the complexity of food systems will be essential for generating evidence on the affordability and availability of food in shaping food choice, diet quality and health.