mindgarden saidMost likely from carbs, not protein. Maybe lactose. Not likely to involve 'artificial sweeteners' - the whole point of them is that they are 10's or 100's of times sweeter than sugar, so there's hardly any of it in there - nothing from which to make gas.
Although any sudden dietary change can cause a temporary re-shuffling of the intestinal biota. It may all settle out in a week or two.
If the gas you're experiencing is the sewer gas schtank we all sometimes get when we eat beans, broccoli, etc, it's possible it's hydrogen sulfide.
We don't all get sewer gas schtank when we eat beans and broccoli.
On a regular basis, I eat refried black beans, mixed with shoestring beats, green beans, and either black eye peas or adzuki beans. It does not give me gas.
And when my mom lightly boils broccoli, I don't let her put anything on it, like butter or seasonings. It doesn't give me gas either.