Though nutritious, some varieties contain more sugar than soda does. Kids should drink water for their thirst, some dietitians say.

Americans have long been hearing the lecture about reducing the amount of soda in their diet. It’s good advice: Sugary soda has no nutritional value and adds nothing to a diet but empty calories and sugar - a 12-ounce can of soda contains a quarter of a cup of sugar.

For many people, the result has been a move to fruit juice, especially for their kids.

Although kids under 12 account for only 18% of the total population of the U.S., they consume 28% of all juice and juice drinks, according to statistics cited earlier this year by the American Academy of Pediatrics’ nutrition committee. A recent study by researchers at the Harvard School of Public Health and published in the Journal of the American Dietetic Assn. found that almost 50% of preschoolers drink 12 ounces or more of fruit juice daily.

Further, juice consumption by children between the ages of 1 and 5 increased by 40% from 1988 to 1998, according to a study in 2002 by researchers at Michigan State University and published in the journal Family Economics and Nutrition Review.

Older kids too are partaking. Schools across the country, including Los Angeles Unified, are pulling soft drinks from their vending machines and replacing them with water and juices. When it comes to taste, juice usually tops water.

Nutritionally, fruit juice is a sound choice. Most juices contain nutrients such as vitamin C, potassium and folate, and some are fortified with calcium and vitamin D.

Fruit juice has a dark side, though. Ounce for ounce, many juices - even those that are 100% pure fruit juice with no added sugar - have more calories and sugar than soda. Twelve ounces of Pepsi has 150 calories; the same amount of orange juice has 165 calories.

“I have one pediatrician friend who calls fruit juice ‘candy water,’ ” says Mary J. Hayes, a pediatric dentist in Chicago and spokeswoman for the American Dental Assn.

“People use a lot of fruit juice because they think it’s healthy - and it is,” says pediatrician Melvin Heyman, professor of pediatrics at UC San Francisco and a member of the American Academy of Pediatrics nutrition committee. “But too much isn’t healthy.”

Calories add up fast when a child drinks juice. A 3-year-old who drinks half a cup of apple juice with breakfast, lunch, dinner and each of two snacks - about 20 ounces total - adds 300 calories to his diet, out of a total recommended intake of about 1,300 calories.

Adults should keep calories in mind when they drink juice too. Those 22-ounce bottles of juice you see in your neighborhood convenience store can pack 300 calories. Smoothies - even those made with 100% fruit and fruit juices - can contain 300, 400 or even 500 calories. That can be fine if you’re having a smoothie as a meal, but probably not if it’s a between-meal snack or post-workout refreshment. A 150-pound person would need to jog for nearly an hour to burn off a good-size smoothie.

The American Academy of Pediatrics recommends that parents limit their children’s juice intake to 4 to 6 ounces a day for children ages 1 to 6, and 8 to 12 ounces a day for children 7 to 18.

Although 100% fruit juice contains more nutrients than soda, the body doesn’t differentiate between the sugar in fruit juice and the sugar in soda. After it is consumed, the sugar in both drinks is converted into glucose, which the body either uses for fuel or stores for future use - in the form of fat.

“Sugar is sugar is sugar,” says Andrea Giancoli, a registered dietitian and a spokeswoman for the California Dietetic Assn.

Teeth don’t differentiate between the sugar in soda and fruit juice either. Naturally occurring bacteria in the mouth feed on the sugars in soda, juice and other sweets, as well as the carbohydrates in starchy foods such as breads and pasta. Within 20 minutes of eating, bacteria in the mouth produce byproducts that bathe the teeth in an acid that eats away at tooth enamel and can cause cavities.

Children who drink too much juice may suffer from digestive problems, including chronic diarrhea, excessive flatulence, abdominal pain and bloating.

If juice replaces the milk in their diets, children may get inadequate amounts of calcium, which is crucial for the development of bones and teeth. Because they drink so much soda and fruit juice, and so little milk, teens are particularly deficient in calcium, which will increase their chances of developing the bone-thinning disease osteoporosis later in life. As many as 90% of teenage girls and almost 70% of teenage boys don’t get enough calcium to ensure strong bones during their adult years, according to the U.S. Department of Agriculture.

“I think we’re going to see a generation of young adults with osteoporosis,” says Giancoli. Low fat or skim milk is best because it provides calcium and other nutrients without all the fat of whole milk.

Instead of drinking fruit juice, kids should eat whole fruit because it provides more nutrients and fewer calories, says Netty Levine, a registered dietitian and nutrition counselor at Cedars-Sinai Medical Center. For example, a medium orange has about 60 calories, and a cup of orange juice has 110 calories. Both give a child a full-day’s supply of vitamin C, but an orange contains more fiber and is more filling than juice, Levine says.

Levine recommends making fruit “user-friendly” so it’s easy for kids and adults to eat. Cut it into bite-size pieces, make fruit salad and have a wide variety of fruit on hand.

When they’re thirsty, kids should drink water, Levine says. “Water is the best thirst quencher of all.”

Switching from juice to water may be hard for some kids. Hayes finds that some of her pediatric dental patients are so accustomed to drinking fruit juice that they refuse to drink water because they find it distasteful. “They expect that all beverages are going to be sweet,” Hayes says. “It’s difficult to untrain a child to drink beverages that aren’t sweet.”

To wean a child off fruit juice, dilute it with water, gradually reducing the amount of juice and increasing the amount of water until eventually, the child is drinking straight water. Or try giving your child water in a sports bottle instead of a cup. “Kids love water bottles,” Levine says.

Ironically, even though fruit juice is high in calories, it can leave you feeling hungry. “Liquid calories don’t satiate you the way solid calories do,” Giancoli says. “It’s more filling to have a whole piece of fruit rather than a glass of fruit juice.”

Although fruit juice is dense in calories, the jury is still out as to whether it contributes to childhood obesity. Some studies suggest a link, but others don’t. That said, though, if an overweight child drinks a lot of juice, reducing juice intake may be a logical way to cut back on calories.

“You can’t blame a single food,” says Theresa A. Nicklas, a childhood obesity researcher and professor of pediatrics at Baylor College of Medicine in Houston. “Overall, what matters is total calories and not where the calories come from.”