There’s no official scientific definition of a superfood, but it’s  accepted that superfoods contain high levels of much-needed vitamins and minerals. They can also be a source of antioxidants, substances that shield our bodies from cell damage and help prevent disease.

Açai Berries :Native to Central and South America. People eat acai berries to address various health conditions. But so far, acai berries have no known health benefit that’s different from similar fruits. If you have pollen allergies or are sensitive to acai or similar berries, you may want to avoid this fruit. When eaten in moderate amounts, though, acai is likely safe.

Goji Berries: A bright orange-red berry that comes from a shrub that's native to China. Some studies using goji berry juice found possible benefits that included a feeling of well being and calmness, better athletic performance and quality of sleep, and weight loss. But those were preliminary studies that need to be repeated before drawing conclusions. All berries are good for you. Goji berries could interact with some drugs. If you take warfarin (a blood thinner), you may want to avoid goji berries. Goji berries may also interact with diabetes drugs and blood pressure drugs, so talk with your doctor first.

Chlorella: A single-celled, water-grown micro-algae, chlorella is widely known as a powerful "superfood" supplement with extraordinary nutrient density

As a medicine, chlorella is used for preventing cancer, reducing radiation treatment side effects, stimulating the immune system, improving response to flu vaccine, increasing white blood cell counts (especially in people with HIV infection or cancer), preventing colds, protecting the body against toxic metals such as lead and mercury, and slowing the aging process.
Chlorella is also used to increase “good” bacteria in the intestine in order to improve digestion; and to help treat ulcers, colitis, Crohn's disease, and diverticulosis.
Some people also use chlorella for the prevention of stress-related ulcers; treatment of constipation, bad breath, and hypertension; as an antioxidant; to reduce cholesterol; to increase energy; to detoxify the body; and as a source of magnesium to promote mental health, relieve premenstrual syndrome (PMS), and reduce asthma attacks. It is also used for fibromyalgia.
Chlorella is applied to the skin for treating skin ulcers, rashes caused by radiation treatment, and a sexually transmitted disease called trichomoniasis

Wheatgrass: The discoveries in the 1930s by US chemist Charles Schnabel, dubbed 'Mr Wheatgrass', have inspired a body of scientific research into wheatgrass that continues to this day.

If you believe the hype, wheatgrass has a higher nutritional content than any other vegetable, protects against inflammation, builds red blood cells and improves circulation.

Wheatgrass contains chlorophyll, vitamin A, vitamin C, vitamin E, iron, calcium and magnesium.

Despite all the health claims, there is very little, if any, evidence that wheatgrass actually works to detoxify or prevent or cure disease. Most of what little research has been conducted focuses on the effects of wheatgrass on the digestive system

Reduce chemotherapy side effects. Although there isn't any scientific evidence that wheatgrass can shrink tumors or increase survival in cancer patients, a preliminary study of 60 women with breast cancer did find that wheatgrass reduced some of the harmful effects of chemotherapy without altering the effectiveness of the treatment

Although wheatgrass is considered safe, some people have reported side effects after using it, especially in high doses. They have ranged from mild (headaches and nausea) to more serious allergic reactions

Watercress is a great example of a superfood that’s a little under the radar. It makes sense: A small plant with delicate leaves, watercress looks so unassuming. But this cruciferous veggie is actually related to horseradish and mustard greens, and all it takes is a taste of raw watercress to discover its potent, peppery spiciness. And when you cook it, watercress releases a surprisingly strong flowery aroma.

Very low in saturated fat and cholesterol, watercress is a great source of

Fiber
Potassium
Protein
Calcium
Magnesium
Folate
Vitamin B6
Vitamin A
Vitamin C

You can enjoy watercress fresh and raw, when its most potent nutrients are in full effect

Chinese Cabbage: Who knew that Chinese cabbage was so super? A recent study by Dr. Jennifer Di Noia of William Patterson University tested and categorized superfoods by their nutrient density. Foods that made the list had to have a measurable amount of potassium, fiber, protein, calcium, iron, thiamin, riboflavin, niacin, folate, zinc, and vitamins A, B6, B12, C, D, E and K in every 100-gram serving size. Chinese cabbage, which includes Napa cabbage and bok choy, came in at number two on the list.
 

What the Researches Say:

Researchers at William Patterson University in New Jersey analyzed 47 types of produce for 17 vital nutrients—potassium, fiber, protein, calcium, iron, thiamin, riboflavin, niacin, folate, zinc, and vitamins A, B6, B12, C, D, E, and K—then ranked them based on their "Nutrition Density Scores

The results are:

• Watercress: 100.00

• Chinese cabbage: 91.99

• Chard: 89.27

• Beet green: 87.08

• Spinach: 86.43

• Leaf lettuce: 70.73

• Romaine lettuce: 63.48

• Collard green: 62.49

• Turnip green: 62.12

• Mustard green: 61.39

• Endive: 60.44

• Kale: 49.07

• Dandelion green: 46.34

• Arugula: 37.65

• Iceberg lettuce: 18.28

Pomegranate: Is a good source of fibre. It also contains vitamins A, C and E, iron and other antioxidants (notably tannins).

A well-conducted trial from 2005 on 45 patients with coronary heart disease demonstrated that a daily 238ml (8.4oz) glass of pomegranate juice administered over three months resulted in improved blood flow to the heart and a lower risk of heart attack. The study did not say what the results mean for conditions such as heart attacks, and with such a small trial the positive results reported could be down to chance.

"A 150ml glass of pomegranate juice counts as one of your 5 A Day. Make sure to avoid brands with added sugar. You could also add pomegranate seeds to cold dishes and salads. It's a healthy and appetising way to increase the nutritional value of your meal."

Spirulina: “Blue-green algae” describes a large and diverse group of simple, plant-like organisms found in salt water and some large fresh water lakes.Blue-green algae are used as a source of dietary protein, B-vitamins, and iron. They are also used for weight loss, attention deficit-hyperactivity disorder (ADHD), hayfever, diabetes, stress, fatigue, anxiety, depression, and premenstrual syndrome (PMS) and other women’s health issues.
Some people use blue-green algae for treating precancerous growths inside the mouth, boosting the immune system, improving memory, increasing energy and metabolism, lowering cholesterol, preventing heart disease, healing wounds, and improving digestion and bowel health.
Blue-green algae are commonly found in tropical or subtropical waters that have a high-salt content, but some types grow in large fresh water lakes. The natural color of these algae can give bodies of water a dark-green appearance
Blue-green algae products are used for many conditions, but so far, there isn’t enough scientific evidence to determine whether or not they are effective for any of them.

How does it work?

Blue-green algae have a high protein, iron, and other mineral content which is absorbed when taken orally. Blue-green algae are being researched for their potential effects on the immune system, swelling (inflammation), and viral infections.

http://www.nhs.uk/Livewell/superfoods/Pages

http://www.webmd.com