The study will be published online December 5, 2013 in BMJ (British Medical Journal) Open.
"People often say that healthier foods are more expensive, and that such costs strongly limit better diet habits," said lead author Mayuree Rao, a junior research fellow in the Department of Epidemiology at HSPH. "But, until now, the scientific evidence for this idea has not been systematically evaluated, nor have the actual differences in cost been characterized."
To address this question, the HSPH researchers conducted a meta-analysis of 27 existing studies from 10 high-income countries that included price data for individual foods and for healthier vs. less healthy diets. They evaluated the differences in prices per serving and per 200 calories for particular types of foods, and prices per day and per 2,000 calories (the United States Department of Agriculture's recommended average daily calorie intake for adults) for overall diet patterns. Both prices per serving and per calorie were assessed because prices can vary depending on the unit of comparison.
The researchers found that healthier diet patterns—for example, diets rich in fruits, vegetables, fish, and nuts—cost significantly more than unhealthy diets (for example, those rich in processed foods, meats, and refined grains). On average, a day's worth of the most healthy diet patterns cost about $1.50 more per day than the least healthy ones.
The researchers suggested that unhealthy diets may cost less because food policies have focused on the production of "inexpensive, high volume" commodities, which has led to "a complex network of farming, storage, transportation, processing, manufacturing, and marketing capabilities that favor sales of highly processed food products for maximal industry profit." Given this reality, they said that creating a similar infrastructure to support production of healthier foods might help increase availability—and reduce the prices—of more healthful diets.
"This research provides the most complete picture to-date on true cost differences of healthy diets," said Dariush Mozaffarian, the study's senior author and associate professor at HSPH and Harvard Medical School. "While healthier diets did cost more, the difference was smaller than many people might have expected. Over the course of a year, $1.50/day more for eating a healthy diet would increase food costs for one person by about $550 per year. This would represent a real burden for some families, and we need policies to help offset these costs. On the other hand, this price difference is very small in comparison to the economic costs of diet-related chronic diseases, which would be dramatically reduced by healthy diets."