A new study by Jennifer Di Noia, an associate professor at William Paterson University, produced a list of the "powerhouse" fruits and vegetables. Those nutrient dense foods are emphasized in the national nutrition guidelines but had never been ranked to show which were actually "powerhouse" foods, until now. 

The top 10 in the study were:

1. watercress

2. Chinese cabbage

3. chard greens

4. beet greens

5. spinach

6. chicory

7. leaf lettuce

8. parsley

9. romaine lettuce

10. collard greens

The top 10 have high levels of vitamins B, C and K as well as iron, riboflavin, niacin and folate. Those nutrients can help protect people from heart disease and cancer.  

Of the 47 foods studied, only six didn't qualify as "powerhouse" food. Those included raspberries, tangerines, garlic and onions. 

The full list is published in Preventing Chronic Disease.