It was believed that artificial sweeteners, due to their intense sweetness, disrupted hunger hormones and encouraged people to eat sweet food.
The study from the University of North Carolina followed 318 overweight and obese adults, who drank at least 280 calories worth of drinks each day, the Daily Mail reported.
One third of the participants substituted two daily servings of sugary drinks with water and another third substituted it with diet drinks, including Diet Coke.
After six months, they reported their food and drink intake over that period.
The study found that water and diet fizzy drinkers reduced their average daily calorie intake at the start of the study from between 2,000 and 2,300 calories to 1,500 to 1,800 calories.
After six months the only differences was that those who drank water ate more fruit and vegetables and those who drank diet fizzy drinks ate fewer desserts.
The study has been published in the American Journal of Clinical Nutrition.