The Science Behind Zero Calories
The zero-calorie label on diet soda comes from FDA regulations that allow rounding down if a product contains fewer than 5 calories per serving. In reality, many diet sodas contain trace amounts of calories from artificial sweeteners and other additives.
Minimal but Present
Though minimal, these calories can add up, especially if you drink multiple servings a day.
Conclusion
Diet soda contains trace calories that may accumulate over time, despite being marketed as zero-calorie.