Standing up after eating will not give you big tummies.
True. IF: you do this all the time PLUS doing other exercises and activities to make you lose those calories you take in everyday. Standing up will make your metabolism work more than sitting down.
The reality you have to face if you want a perfectly nice healthy body is for you to take the right amount of calories for your height and daily physical activity; and for you to have ways in burning them like routine exercise and physical movements.