How long after you eat is it safe to do sit ups?

I always find I get motivated to do exercise, my favourite being sit up, more or less right after breakfast... but I always get put off by knowing that it's not good for you to do an exercise like that after eating. How long should I wait? x

I would give it 1/2 an hour to an hour before doing exercise after eating

Thanks Just realised i posted this on the wrong thread... opps! x