Why it is not advisable to drink soft drinks when one is hungry?

The carbonation in soft drinks makes it harder to gulp down enough fluids and may cause indigestion. The high sugar content of soda (and some juices) causes insulin levels in your blood to rise, which leaves you feeling sleepy and tired. Drinks containing caffeine and/or alcohol will increase fluid loss, which may contribute to dehydration.

http://www.danvillesoccer.com/cparentshydrationandnutrition.htm