The artificial sweeteners are what create the gas and diarrhea. Sweeteners can affect people differently but more importantly it's the quantity that they eat.

If I have a couple sugar-free Lifesavers I'll fart a little bit more. If I say at the whole bag of sugar free gummy bears in 10 minutes well then I would be running to a toilet soon.

It's the surprise element. Most people don't know these things so they eat a bunch like normal then quickly realize their mistake.