The new study used a combination of nutrient profiling methods and national food prices data to create an 'affordability index'. This was then used to examine the nutrients per unit cost of 98 individual vegetables as well as five vegetable subgroups including dark green, orange/red, starchy, legumes, and 'other' vegetables.
Led by Dr Adam Drewnowski from the University of Washington, USA, the results reveal that potatoes offer one of the best nutritional values, provide one of the better nutritional values per penny - more than most other raw vegetables - and deliver one of the most affordable source of potassium of the more frequently consumed vegetables (second only to beans).
"The present calculations, thus far limited to vegetables, illustrate how the econometric approach to nutrient profiling can help identify affordable nutrient-rich foods within each food group," said Drewnowski and his colleagues.
These metrics of affordable nutrition used by the study could help policy makers, families, food manufacturers and food service workers to identify vegetable subgroups that provide the best nutritional value per penny, they added.
"The ability to identify affordable, nutrient dense vegetables is important to families focused on stretching their food dollar as well as government policy makers looking to balance nutrition and economics for food programs," said the lead researcher. "And, when it comes to affordable nutrition, it's hard to beat potatoes."
The research was supported, in part, by the US Potato Board, however the authors added that the funders "had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript."
The team calculated food costs per 100 grams, per 100 calories, and per edible cup and then used nutrient density measures based on six nutrients: dietary fiber; potassium; magnesium; and vitamins A, C, and K. Individual nutrient costs were measured as the monetary cost of 10% daily value of each nutrient per cup equivalent.
The results indicated while dark green vegetables had the highest nutrient density scores, after accounting for cost, starchy vegetables (including potatoes) and beans provided better nutritional value for the money.
Potatoes, in particular, provide one of the lowest cost options for four key nutrients including potassium, fibre, vitamin C and magnesium.
Among the most frequently consumed vegetables, potatoes and beans were the lowest-cost sources of potassium and fibre, the authors noted.
Fresh, frozen, and canned vegetables had similar nutrient profiles and provided comparable nutritional value, they said.