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It seems good ol' apple, orange and grapefruit juice are getting the squeeze.

Blueberry, cranberry, pomegranate, açai, mangosteen and goji are just some of the new breeds of juice taking up space on grocery and health-food store shelves.

Chances are you've heard the claims: Blueberry juice fights Alzheimer's disease, cranberry wards off bladder infections, pomegranate halts prostate cancer.

But do these juices really fend off disease? Or are they just nutritious - and expensive - alternatives to orange juice?

The potential health benefits of "super juices" centre on their antioxidant power. Antioxidants such as vitamin C, vitamin E, selenium and plant (phyto) chemicals destroy free radicals, unstable oxygen molecules that are formed during normal metabolism. If left unchecked, free radicals can damage cells and may lead to cancer, heart disease, cataracts, arthritis and Alzheimer's.

According to a 2006 study that measured the antioxidant content of foods commonly eaten in the United States, blackberries, strawberries, cranberries, raspberries, blueberries, cranberry juice, blueberry juice and cranapple juice were among the top 50 foods containing the most antioxidants per serving. (So were orange, apple and grape juice.)

Some manufacturers have used such antioxidant measurements to help sell their products. A website selling açai juice states the açai fruit possesses "around 30 times more antioxidants than red wine." Another site claims that noni juice has antioxidant results "similar to those of green tea."

But just because a food has a high antioxidant content doesn't mean it will translate into a health benefit - some antioxidants may not be absorbed and utilized in the body. The only way to know is to test whether antioxidants can neutralize harmful free radicals in humans and whether they help lower the risk of disease.

Here's what the science says about today's new super juices:

Cranberry juice

There is evidence from four well-controlled trials that cranberry juice significantly cuts the number of urinary tract infections over a 12-month period, particularly in women with recurrent infections.

Cranberries contain flavonoids, some of which prevent certain bacteria, including E.coli, from adhering to the bladder wall. Lab studies suggest the anti-adhesion properties of cranberry juice may also inhibit bacteria associated with gum disease and stomach ulcers caused by H. pylori bacteria.

Studies also demonstrate the ability of cranberry antioxidants to protect low-density lipoprotein (LDL) cholesterol - bad cholesterol - from being oxidized by free radicals. (Oxidized LDL is considered more dangerous because it readily sticks to artery walls.)Blueberry juice

Blueberries also contain flavonoids, which research suggests may boost brain power - at least in mice. Researchers found that diets rich in blueberries - the equivalent of one cup a day for humans - significantly improved both the learning capacity and motor skills of aging animals, making them mentally equivalent to much younger ones.

Research of animals also suggests that blueberries are good for the heart by making blood vessels more resistant to oxidative stress and lowering blood cholesterol.

Pomegranate juice

Like other fruit juices, pomegranate juice contains antioxidants, especially polyphenols. Research conducted by the makers of POM Wonderful pomegranate juice found that antioxidants in it were much more potent than those in red wine and other juices.

In a study of 45 patients with coronary heart disease, those who drank 250 millilitres of POM daily for three months had improved blood flow to the heart. Another study found drinking pomegranate juice each day for one year reduced blood pressure, decreased oxidation of LDL cholesterol and reduced clogging of arteries that supply the brain.

Pomegranate juice may also slow the progression of prostate cancer. A preliminary study, published last year in Clinical Cancer Research, found that, after treatment for prostate cancer, the length of time it took for prostate-specific antigen to double was significantly longer in men who drank 250 ml of pomegranate juice daily for up to two years.

However, these studies are based on small numbers of people. While it's too soon to say that drinking pomegranate juice prevents disease, it's certainly a nutritious addition to your diet, although a 473-ml bottle of POM sells for $4.99 - more than four times the price of orange juice and containing twice the calories a serving.

Açai juice

Harvested in the rain forests of Brazil, açai berries are a rich source of flavonoids. Two lab studies of açai berry extracts suggest that açai juice may have anti-inflammatory effects in the body. And preliminary research from the University of Florida found that açai extracts reduced the growth of human leukemia cells.

A 32-ounce (946 ml) bottle of 100-per-cent açai juice costs $80. A more affordable option is President's Choice grape and açai juice blend.Mangosteen juice

Native to Southeast Asia, mangosteens contain xanthones, antioxidants that stop the growth of certain bacteria and fungi in lab tests. So far there have been only a few experiments in animals and test tubes, but no human clinical trials. Many of the claims are based on anecdotal evidence. Some brands sell for as much as $55 for a 946-ml bottle.Goji juice

Websites selling goji juice boast of the berry's immune-boosting and anti-cancer properties. It's even purported to enhance human libido and keep people feeling young, abilities attributed to the berry's polysaccharide and nutrient content. Published animals studies have shown goji berry extract to boost high-density lipoprotein cholesterol - good cholesterol - in rabbits, improved insulin resistance in diabetic rats and reduced oxidated stressed in aging mice. Studies in humans are lacking. Goji juice isn't cheap; store brands sell for $55 to $68 for a 946-ml bottle.

Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Visit her website at Lesliebeck.com.