Juice has come a long way from the simple glass of OJ you drank as a kid. The newest cold-pressed juices blend together kale, spinach, ginger and beets -- just about any combination you can think of, and they promise not just an explosion of taste, but a boost of more vitamins, antioxidants and balanced pH.

But are cold-pressed juices wholesome bottles of nutrition or overpriced jars of hype?

Whether cold-pressing is a superior method of juicing depends on who you ask. Most juices are made by grinding fruit or vegetables with spinning metal blades, separating the juice from the pulp.

Cold-pressed juice advocates say the resulting juice is less nutritious because the blades introduce heat and air which causes the juice to oxidize and thus reduces its vitamins and enzymes.

Cold-pressing, on the other hand, uses intense hydraulic pressure to extract juice slowly. That keeps more of the juice’s nutrients and enzymes intact because there’s no heat or oxygen involved, say advocates.

The problem is there is no evidence that cold-pressed juices are any more nutritious than regular juices or smoothies, says Toronto-based registered dietitian Sue Mah. She searched to see what kind of studies had been done on cold-pressed juice and didn’t find much.

“I would love to see a study comparing the nutrition content of a cold-pressed juice versus a frozen or regular fresh juice,” she said in a telephone interview with CTVNews.ca.

“But you know, even if there is a difference, I would guess that the difference is minimal.”

Mah says there’s a simple way to be sure you get all the micronutrients out of fruits and vegetables: simply eat them whole. She worries that shoppers are grabbing these bottles of juice thinking they are getting their daily fruits and vegetables servings.

“My fear with these drinks is that consumers will drink these and think that’s all they need to get their vegetable and fruit nutrition. That’s not how it works,” she said.

“Even if we were absorbing a little more nutrients from these cold-pressed juices, it doesn’t mean we can skip eating fresh fruits or vegetables.”

For one thing, she says, cold-pressed juices -- and juices in general -- are sorely lacking in fibre, which is lost when the skin is removed and the pulp extracted. And all of us could use more fibre in our diets, not less.

As an example, she notes that an apple has about 4 grams of fibre, most of it in the skin. To get the same amount of fibre from apple juice, we’d have to drink eight cups.

“Who would want to drink that amount of juice? That’s a lot of calories,” she says.

Without that fibre, it’s too easy to drink down a lot of liquid calories without feeling full, she says. And many of the fruit juice blends have tons of naturally-ocurring sugar as well.

That’s why kids are advised to drink no more than ½ cup of juice a day and why adults should have no more than 1 cup a day, Mah says.

She also worries about the fact that some cold-pressed juices are not pasteurized, as commercial juices are.

Fresh juice advocates say the sterilization process destroys nutrients, so juices are sold fresh, which means they must be consumed within three days of juicing.

Other cold-pressed juice brands, such as those sold in refrigerated areas of coffee chains, have undergone “high pressure processing,“ which uses intense pressure machines to inactivate pathogens such as listeria.

Mah says it worries her when juices aren’t pasteurized

“There’s a little bit of food safety risk without the pasteurization,” she said. “You can get bacteria growing, and you won’t see it or smell it, but it can make you sick.”

Pregnant women and those who are immuno-compromised have long been advised to avoid unpasteurized juices, so she recommends they stay away from freshly pressed juices.

Then there’s the aspect of cost. With some cold-pressed juices going for $10 a bottle, Mah thinks there are probably better ways to spend your money.

She was recently at the grocery store checking prices and noticed that for the same amount of money as a big bottle of cold-pressed juice, a shopper could buy a bag of carrots, a head of lettuce or kale, a pound of apples, a pound of bananas, and maybe a pound or two of pears.

“So I could get all of that amazing fresh and filling fruits and vegetables, or one bottle of juice?” she asked.

“With high food costs when budgets are tight for everyone, that’s an important consideration. Save your money and buy healthy wholesome fruits and vegetables instead.”