A new study of 47 foods awarded the "watercress" as No. 1 on the list of powerhouse fruits and vegetables (PFV) with a perfect 100 score.

"Powerhouse" is a term used by researchers from William Paterson University in Wayne, NJ to describe fruits and vegetables, such as green leafy, yellow or orange, citrus and cruciferous items, which could strongly reduce one's risk to chronic diseases. While there is an existing list of powerhouse items, there is none that ranks the fruits and vegetables based on their nutritional value.

Researchers began the review by creating a tentative list of PFVs based on scientific data and consumer guidelines. After creating a list, the analysts calculated the nutrient density score of each food based on 17 nutrients including potassium, fiber, protein, calcium, iron, thiamin, riboflavin, niacin, folate, zinc and vitamins A, B6, B12, C, D, E, and K. The last step of the ranking process was the classification of foods based on the standards set by the U.S Food and Drug Administration (FDA). The federal agency approved those that scored 10 percent and above to be listed as PFV.

"The score is a nutrient-to-calories ratio," said Jennifer Di Noia, lead author of the study and an associate professor of sociology at William Paterson University, to LiveScience. "This study is the first of its kind to define and rank powerhouse fruits and vegetables."

Out of 47 fruits and vegetables studied, six failed to meet the PFV classification. These included the raspberry, tangerine, cranberry, garlic, onion, and blueberry. About 97 percent of the PFVs could help reduce risks to cardiovascular, neurodegenerative diseases, and some cancers. The upper half of the list included Chinese cabbage, collard green, kale, arugula) and green leafy (chard, beet green, spinach, chicory, leaf lettuce), with watercress sitting on the top spot. The lower half included carrot, tomato, winter squash, sweet potato, scallion, leek, citrus lemon, orange, lime, grapefruit, strawberry, and blackberry, CDC reported.

Health experts believe that the results of the study could help consumers make better food choices and look at the green leafy vegetables differently.

The results of the study were published on the June 5 issue of the CDC's Preventing Chronic Disease.