Researchers at Harvard have found that eating fruits, vegetables, fish and whole grains cost about $1.50 more per day than the least healthy diets.
That means that families would pay an extra $550 per year to eat better - a significant strain on low-income earners.
“People often say that healthier foods are more expensive, and that such costs strongly limit better diet habits,” said study author Mayuree Rao at Harvard's public health school.
“But, until now, the scientific evidence for this idea has not been systematically evaluated, nor have the actual differences in cost been characterized.”
The study looked at 27 separate analyses from 10 high-income countries, investigating the cost of healthy versus unhealthy diets.
Adjusting for calorie sizes and servings, the researchers found that diets rich in fruits, vegetables, fish, and nuts were often significantly costlier than those with processed foods.
The reason, researchers say, is probably due to food subsidies of inexpensive, high-value staples like corn and wheat.
These ingredients are often refined to create cheap, long-lasting food but without much nutritional value.
Researchers said the results proved that for some families, eating well would cost more but they pointed out that disease resulting from bad nutrition is also costly.
"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," said study author Dariush Mozaffarian.
The study was published Saturday in the British Medical Journal.