Sugar and caffeine are both a source of controversy. The problem with empty calories is that it keeps you from eating other foods that are more nutritious and beneficial to your health. The other faction says that sugar is an evil that has detrimental physical and mental effects and it should be avoided at all costs. For more information on sugar, see Sugar and its effects . Since sugar is a carbohydrate, it can be used by the body for energy, or if consumed in excess it can be converted to fat.
Caffeine is another source of debate.
On the positive side, caffeine does improve mental alertness. Much of the research on the long-term effects of caffeine have found that drinking the equivalent of 2 cups of coffee daily seems to have no detrimental health consequences. Take into consideration however, that it is really difficult to conduct this type of long term research, because it's hard to track a significant number of people over time, and because there are so many competing factors to control for, such as smoking, alcohol use and stress, making it hard to determine which factor causes what long term effect. Caffeine, like sugar is something you'll have to decide which side of the debate to stand on. In a larger context, the transportation, processing, packaging and marketing of soda has a huge negative impact on the environment.