Nutrient-dense foods have a high nutrient/calorie ratio. Meaning they are rich in nutrients when compared to their calorie content.
A good example of a nutrient-dense food is strawberries. One cup of strawberries contains only 150 calories, but 3.5g fiber, a massive 86mg of vitamin C and a useful 26.9mcg of folate.
Nutrient-dense foods are the oppposite of empty-calorie foods which are low in nutrition when compared to their calorie content.
Food fulfills three basic needs: (1) to provide energy; (2) to support new tissue growth and tissue repair; and (3) to help regulate metabolism. These three requirements are met by components of foods called "nutrients", which consist of six classes: carbohydrates, fats, proteins, vitamins, minerals, and water.
Foods that are "nutrient dense" supply a significant amount of these nutrients for their calories. A high-performance diet emphasizes nutrient-dense carbohydrates necessary to maintain muscle glycogen - the primary fuel for most sports.
1. Spirulina
Spirulina is a type of blue-green algae that is rich in protein, vitamins, minerals, and carotenoids, antioxidants that can help protect cells from damage. It contains nutrients, including B complex vitamins, beta-carotene, vitamin E, manganese, zinc, copper, iron, selenium, and gamma linolenic acid (an essential fatty acid).
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2. Kale
According to Dr. Joel Fuhrman, kale is the most nutritious food, loaded with minerals, vitamins, fiber and amino acids, as well as important antioxidants that reduce inflammation and can prevent cancer. It's also delicious and an easy to prepare, versatile food.
Since kale is rich in vitamins and minerals like calcium, potassium, iron and have anticancer properties. This makes it perfect for juicing. Kale is also rich in fiber and detoxifies your entire system. You should select kale that is fresh, dark green and tender.
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3. Hemp Seeds
Hemp is considered one of the world's most nutritious plants. Hemp seeds contain all of the essential amino acids making them an ideal source of protein for vegans. The essential fatty acids are abundant in hemp seeds and come in a ratio that is highly beneficial to humans. Magnesium, iron, and potassium are in good supply along with fiber. You can use hemp seed oil on your salads. You shouldn't use hemp seed as a frying oil or high heat oil.
4. Chocolate
Yes, you read right. Cacao beans are so nutrient-dense that scientists haven't even begun to identify all the benefits in the little bean yet. Don't grab a Snickers though—the good stuff is found only in raw cacao beans or nibs (or really, really dark 
chocolate). Minerals, vitamins and tons of antioxidants are great for your heart, skin, and release chemicals in the brain that make you feel like you're in love.
5. Broccoli
Broccoli is a member of the cabbage family. It is one of the most nutrient dense foods. Packed with vitamin C and has anticancer effects. When selecting broccoli to juice, look for dark green broccoli or purplish heads. The stalks should be firm. Avoid broccoli with wilted, yellow or soft leaves since their nutritional content is low.
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6. Spinach
Spinach is packed with powerful nutrients. Spinach has fiber, flavonoids which have anticancer properties, antiflammatory properties due to neoxanthin and violaxanthin properties, lowers blood pressure, packed with vitamin A which helps with immunity and skin complexion, and vitamin K. Choose dark green and fresh spinach. Fresh or cooked, spinach's sweet and hardy flavor brightens any meal.
7. Chia
The chia seeds are “super” because, like a superfruit, they deliver the maximum amount of nutrients with minimum calories. They have several of the same benefits as the more well-known “super seed” flax, but unlike flax seed, you don’t need to grind them to reap the health benefits. The nutritional benefits of chia include fiber, omega fatty acids, calcium, antioxidants and much more – even protein!
8. Blueberries
The USDA ranked blueberries #1 out of 40 common fruits and vegetables that are rich in antioxidants. Blueberries are believed to lower cholesterol, prevent urinary tract infections, and improve memory, eyesight, balance and coordination, in addition to slowing signs of aging and reducing the risk of heart disease and diabetes.
Source:
Types of Berries - Find Facts About Berries at WomansDay.com - Woman's Day
http://www.umm.edu/altmed/articles/spirulina-000327.htm
http://vegetarian.about.com/od/beverage1/a/what-are-hemp-seeds.htm
