is it, though?
a stomach can stretch upto 4 litres in capacity when pushed (one source). that's 4000cm³ (or 244 cubic inches).
to fill that capacity, the volume of a pizza needs to be 4000cm³ or 244 inch³.
take πr²h = 4000 for thin crust pizzas, if we assume the average height of pizza and toppings as 1cm, our equation simplifies to πr² = 4000; which gives the radius of the pizza as around 36 cms -- or a diameter of 72 cms (or 28").
if we take a thicker pizza of an average crust thickness of 1", then our equation for square inches simplifies to πr² = 244. which gives us a radius of about 9" or a diameter of 18".
since most pizzas top out at 12"-14" diameter (thin and thick crust volume varying between 700cm³ to 2600cm³), if anything, we're nowhere near achieving our full potential!