Ask the nutritionist.

Why does our increased intake of soda contribute so significantly to weight gain?
Since humans have not adapted to drinking sweet and sugary beverages, the current increase in consumption and added calories may be significantly contributing to the growing number of overweight and obese people in the United States. Both portion sizes and number of servings have increased.
Decreasing the consumption may be part of the solution. In fact presently there are two working theories as to why. They follow.
1. Humans evolved drinking breast milk and water therefore we do not have good physiological systems to metabolize other beverages. We are maladapted to digest calories from sweet juices and sodas.
2. Humans have an incomplete satiation sequence for sweetened beverages which prevents us from becoming satiated when we drink them. There is evidence that beverages send weak satiety signals. Studies of hunger, fullness, and further eating support the view that fluids are less satiating than solid foods.
One study found that when groups ate 450 calories of jelly beans or drank 450 calories of sweetened fruit drink, the group that drank the calories gained more weight. The mechanisms for this weaker compensatory response to fluids are not known.
So, drink water, a bit of coffee or tea and low fat milk.