Registered dietitian Charlotte Scott says almost all of her overweight clients drink a lot of soda.
That concerns her -- and it all starts with the empty calories.
"Soda displaces healthier options. People get caught up on soda and diet soda," said Scott, of McKay-Dee Hospital. "I say, 'Just bag it.' Don't drink it. There is no nutritional value, and regular soda has extra calories. Let's look at the bigger picture."
In a study for the Center for Science in the Public Interest, Michael Jacobson said Americans are getting too many calories from soda.
"Americans consume gargantuan quantities of carbonated soft drinks and suffer untoward health consequences," he said. "Companies annually produce enough soda pop to provide 52 gallons to every man, woman and child.
"Carbonated soft drinks are the single biggest source of calories in the American diet, providing about 7 percent of calories. Teenagers get 13 percent of their calories from carbonated and noncarbonated soft drinks."
Too much sugar
Nutrition experts agree that calories should be coming from what you eat, not what you drink.
"Soda is a man-made beverage concoction, with man-made chemical additives such as high fructose corn syrup," said Jennifer Turley, professor of nutrition at Weber State University, in an e-mail interview.
"Drinking sugary soda and other beverages high in sugar ... adds calories quickly to the body and doesn't send the same messages to the brain that food does to tell the person when they are full and should stop eating or drinking,"
Even diet soda can affect the body's appetite and keep people from making better food choices, Scott said.
"The key is moderation with diet soda. The best fluid is water, and it costs a lot less," she said.
Shelly Costly, coordinator of the dental hygiene program at Weber State University, said a soda drinker has more to worry about than his/her waistline: The sugar in soda interacts with the bacteria in the mouth and causes decay.
The acid in both regular and diet soda also eats away at the teeth and is especially bad in clear sodas, Costley said.
Scott said any kind of soda is usually taking the place of something more nutritious, like milk.
In the 1970s, Jacobson said, teenagers were consuming twice as much milk as soda, but in the 1990s soda won out over milk 2-to-1.
"Heavy soft-drink consumption is associated with lower intake of numerous vitamins, minerals and dietary fiber. ... Frequent consumption of soft drinks may also increase the risk of osteoporosis, especially in people who drink soft drinks instead of calcium-rich milk," he said.
Some of the ingredients in soda may put further stress on the bones, Turley says.
"Soda is not a good source of essential nutrients, like calcium and vitamin D, that the body needs to stay alive," she wrote. "Some dark sodas provide a source of phosphorus, an essential nutrient for the body that is found abundantly in animal and processed foods. When a person eats too much phosphorus and not enough calcium, then they are setting their bones up for failure later in life because (that) combination is associated with calcium depletion from the body and bone loss."
In a news story posted at the U.S. Department of Agriculture's Web site, David Milne recommends moderation:
"There is a way to have soda and keep the fizz in your bones. One or two sodas a day may be OK. However, people also need to eat foods that are rich in calcium and magnesium. Carbonated drinks have a place, but in moderation. However, to assure healthy bones and quality of life, we must pay attention to the other beverages we drink and foods we eat."
Carbonation vs. caffeine
Of all of the problems with soda, carbonation may be the one getting the worst rap. Although many athletes feel strongly that carbonation slows them down, Caroline Shugart of Utah State University's employee wellness program, said that probably isn't true.
"I've heard rumors about carbonated beverages, but not any definitive conclusion as to their effect on performance. For some, carbonation may lead to an upset stomach, especially in swimmers, and burping in runners, but I don't think it affects blood gases or energy metabolism in any way. The body is very well equipped to deal with CO2," she said in an e-mail interview.
Scott said no studies show carbonation has a harmful effect on the body. Jacobson says the real soda villain may be caffeine.
"The amounts of caffeine in soft drinks can have distinct pharmacological and behavioral effects. Caffeine can increase alertness, an effect that many people desire. However, caffeine also can cause nervousness, irritability, sleeplessness and rapid heartbeat. It causes children who normally do not consume much caffeine to be restless and fidgety, develop headaches and have difficulty going to sleep," he said.
"Caffeine's addictiveness, in fact, may be one reason why six of the seven most popular soft drinks contain caffeine."
The American Dietetic Association says that moderate amounts of caffeine cause no harm, but excessive amounts can cause anxiety, insomnia, headaches or stomach irritation. The Mayo Clinic says caffeine may be yet another problem for bones.
"The link between osteoporosis and caffeinated sodas isn't clear, but caffeine may interfere with calcium absorption and its diuretic effect may increase mineral loss. In addition, the phosphoric acid in soda may contribute to bone loss by changing the acid balance in your blood. If you do drink caffeinated soda, be sure to get adequate calcium and vitamin D from other sources in your diet or from supplements," according to a report at www.mayoclinic.com.