Higher-quality meat accounts for much of that cost differential. Kale's cheap, and staples such as grains, dairy, snacks/sweets, juices/sodas and fats/oils don't tend to vary much in price.
Researchers from the Harvard School of Public Health analyzed the prices of healthy foods and diet patterns, compared to less healthy options, from 27 studies in 10 countries. The study was published online yesterday in BMJ (British Medical Journal) Open.
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).
"People often say that healthier foods are more expensive, and that such costs strongly limit better diet habits," lead author Mayuree Rao said in a statement. "But, until now, the scientific evidence for this idea has not been systematically evaluated, nor have the actual differences in cost been characterized."
The scientists looked at the difference in prices per serving and per 200 calories for certain food types, as well as prices per day and per 2,000 calories (the recommended average daily calorie intake for adults).
They found that meats and proteins had the largest price differences, with healthier options costing about $0.29 more per serving and about $0.47 more per 200 calories than less-healthy options. Price differences for other food groups, such as grains, dairy, snacks and sweets, and fats and oils, were much less significant, ranging from $0.02 to $0.12.
"This is especially crucial for socioeconomically disadvantaged populations, who have less healthy diets and higher disease risk than higher socioeconomic groups," the study said.
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. (Don't hold your breath.)
Lowering the price of items found in healthier diets, the authors wrote, should be "a goal of public health and policy efforts."
Although the price difference might not seem that great, "This would represent a real burden for some families, and we need policies to help offset these costs," senior author Dariush Mozaffarian said in the statement. "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."
(Of course, everything's relative. It is possible to spend a great deal of money on a very unhealthy diet, too: foie gras, caviar with crème fraiche, triple-cream Brie, chocolate truffles -- just to name a few of our favorite things.)