Not necessarily. It depends on how many situps and how much food you eat after. If you just do a couple of sets of 50 to 100 situps, food afterward should go down without any discomfort. Keep in mind that endurance athletes such as those running a marathon eat/drink while exercising.
You should eat something or have a drink which can give you energy for doing lot of sit ups. Eating heavily just before or just after sit ups will be uncomfortable to you.
You have to have fixed times for your food intake such as breakfast, lunch and dinner and one light snack if you are hungry between major meals.
Now just do not eat a major meal just for the sake you have done lot of sit ups.
These instructions I am giving keeping in mind that you are trying to keep yourself in proper shape and normal BMI.
If you are already fit you can occasionally dig into food propelled by your cravings.
yes i am eating so much after i do lots of sit ups more than 50...