Outliers: Sounding an alarm on juicing

That $9 green juice might be rotting your teeth, spiking your blood sugar and harming your relationship with food, in addition to emptying your wallet.

While bright-green elixirs of liquefied kale, cucumber, ginger and the like have become so popular they're threatening to supplant artisanal coffee as the daytime beverage of choice for well-heeled Americans, medical experts are questioning whether drinking your veggies is a good idea.

One of the most prominent and forceful voices against juicing is Dr. David Agus. Best known as the physician who counseled former Apple CEO Steve Jobs through his cancer treatment, Agus is a professor at the University of Southern California's Keck School of Medicine.

He says the act of squeezing fruit and veggies to smithereens in the juicer exposes the flesh to air, instantly beginning the process of oxidation and degradation of nutrients. “Most of the nutrients are very sensitive to both oxygen and light,” Agus said.

The degradation process also makes the sugars more available to the body, he says, which produces an insulin spike that causes inflammation and can increase the risk of cancer. Plus, regularly consuming the large quantity of produce required to make a

12-ounce juice goes against time-tested advice in favor of moderation. “Our bodies aren't made to eat six carrots,” Agus says. “We're not made to absorb the nutrients.”

Overdoing it isn't great for teeth, either. “The biggest problem with juicing is really the sugar content,” said Dr. Kevin Dow, a dentist in downtown Chicago. “When it mixes with the bacteria in your mouth, it forms acids that lead to tooth decay.”

Agus said no data exist to prove any of the benefits commonly associated with juicing. Dr. Clyde Yancy, chief of cardiology at Northwestern University's Feinberg School of Medicine, agreed. “It's not as healthy as it would appear to be at first glance,” he said. A purely liquid diet does not contain sufficient protein and can disrupt cellular function when potassium levels dip too low, Yancy said.