Regular sodas and other sugar-sweetened beverages contribute to weight gain and the obesity epidemic. Sodas contain 140 to 150 calories (all from sugar) in a 12-ounce can, and people often drink 20-ounce bottles at one sitting. Yet because sodas (like all liquids) are not satiating, people who drink them do not typically reduce calories elsewhere. If you add just one can of regular soda a day to your diet, everything else being equal, you’ll gain 15 pounds in a year. Even if you’re not watching your weight, there’s no reason to fill up on these “empty” calories.
A 12-ounce can of soda contains the equivalent of 10 teaspoons of sugar, typically in the form of high-fructose corn syrup (HFCS). Whether this cheap sweetener is worse than other sugars is debatable. Some researchers say it has different metabolic effects in the body, impairing blood sugar control and possibly stimulating appetite. But others say that differences are minimal, and that it’s the quantity of sugar, not the type, that’s the real problem. More likely, HFCS contributes to weight gain and diabetes because it is prevalent and provides excess calories.
100 percent fruit juices may have as many calories as sodas and other sweetened soft drinks, but they also contain vitamins, minerals, phytochemicals and, if the whole fruit is used, some fiber. Still, you should limit juice—and eat more whole fruits instead, because they retain all their nutrients and are more filling. Aim for no more than one daily cup of fruit juice.
Some research suggests that sodas can trigger gastric reflux (heartburn), though people react differently to different foods, and not everyone with reflux has a problem with soda. Carbonation distends the stomach, while caffeine, if present, relaxes the sphincter at the top of the stomach, allowing acid and food to move back up into the esophagus and throat.
All sugary foods, including sodas, can cause tooth decay, especially if you consume them frequently and don’t brush regularly, though sticky foods tend to be worse than beverages. Sodas (including diet) are also acidic and, like any acidic food or beverage, can break down tooth enamel. For most people, this is not a concern, but those with chronic dry mouth have less saliva to wash away the acids.
Several studies have noted a link between cola consumption and decreased bone density. One theory is that the phosphoric acid in regular and diet colas (usually not present in other sodas) reduces calcium levels in the body, thereby increasing the risk of bone loss. However, some researchers believe sodas contribute to bone loss because they take the place of milk and other beverages that supply nutrients important for bone health.
Sugar substitutes in diet sodas (typically aspartame, acesulfame K or sucralose) are safe, according to the Food and Drug Administration and other regulatory authorities worldwide, based on years of research. Several years ago, an Italian animal study linked even “safe” doses of aspartame to cancer. But the European Food Safety Authority has since reconfirmed the sweetener’s safety, citing study flaws. Diet soda labels warn people with phenylketonuria (PKU), an uncommon genetic disorder, to avoid aspartame.
Though diet sodas contain no calories, it’s unclear whether they actually help in weight loss, especially over the long term, because so many factors come into play. A well-designed study in the American Journal of Clinical Nutrition found that when overweight or obese adults substituted diet drinks for at least two servings of caloric beverages a day, they lost a little more weight than those who did not switch beverages. But according to other studies, some people may compensate by eating more later on. And diet sodas won’t help you lose weight if you simply add them to your current diet.