To many people, it's a health food. To others, it's simply soda in disguise.

That virtuous glass of juice is feeling the squeeze as doctors, scientists and public health authorities step up their efforts to reduce the nation's girth.

It's an awkward issue for the schools that peddle juice in their cafeterias and vending machines. It's uncomfortable for advocates of a junk-food tax who say they can't afford to target juice and alienate its legions of fans. It's confusing for consumers who think they're doing something good when they chug their morning OJ, sip 22-ounce smoothies or pack apple juice in their children's lunches.

The inconvenient truth, many experts say, is that 100% fruit juice poses the same obesity-related health risks as Coke, Pepsi and other widely vilified beverages.

With so much focus on the outsized role that sugary drinks play in the country's collective weight gain -- and the accompanying rise in conditions including diabetes, heart disease and cancer -- it's time juice lost its wholesome image, these experts say.

"It's pretty much the same as sugar water," said Dr. Charles Billington, an appetite researcher at the University of Minnesota. In the modern diet, "there's no need for any juice at all."

A glass of juice concentrates all the sugar from several pieces of fruit. Ounce per ounce, it contains more calories than soda, though it tends to be consumed in smaller servings. A cup of orange juice has 112 calories, apple juice has 114, and grape juice packs 152, according to the U.S. Department of Agriculture. The same amount of Coke has 97 calories, and Pepsi has 100.

And just like soft drinks, juice is rich in fructose -- the simple sugar that does the most to make food sweet.

UC Davis scientist Kimber Stanhope has found that consuming high levels of fructose increases risk factors for heart disease and Type 2 diabetes because it is converted into fat by the liver more readily than glucose. Her studies suggest that it doesn't matter whether the fructose comes from soda or juice.

"Both are going to promote equal weight gain," she said, adding that she's perplexed by the fixation on the evils of sugar-sweetened beverages: "Why are they the only culprit?"

Juice is a relatively recent addition to the human diet. For thousands of years, people ate fruit and drank mostly water.

But in the early 1900s, citrus growers in Florida were harvesting more oranges than they could sell. Then they had an epiphany: promote juice.

"You consume more oranges if you drink them than if you eat them whole," said Alissa Hamilton, author of the book "Squeezed: What You Don't Know About Orange Juice."

The U.S. Army was instrumental in turning orange juice into a commercial product.

It originally served a powdered lemonade to ensure soldiers got enough vitamin C, but it tasted "like battery acid," Hamilton said. So, during World War II, the Army commissioned scientists to invent a system for freezing OJ in a concentrated form. The patent wound up with Minute Maid, which sold cans of frozen juice concentrate in grocery stores.

In the 1950s, pasteurization technology developed by Tropicana made orange juice even more consumer-friendly because it could be sold ready to drink in cartons, like milk.

TV fitness pioneer Jack LaLanne and other health experts touted juice as a natural medicine, and decades of advertising helped secure its place at the breakfast table. Today, roughly half of all Americans consume juice regularly, according to NPD Group, a market research firm.

The Juice Products Assn. emphasizes the value of the vitamins, minerals and phytonutrients in juice, especially when so many Americans eat so little fresh produce.

"If someone can add a glass of fruit juice at breakfast, that's an important addition to the diet," said Sarah Wally, a dietitian for the trade group.

But scientists are increasingly questioning whether the benefits outweigh the sugar and calories that come with them. "The upside of juice consumption is so infinitesimal compared to the downside that we shouldn't even be having this discussion," said Dr. Robert Lustig, a pediatric endocrinologist at UC San Francisco.