And what are some good sources for these extra short-chain fatty acids?
Fermentable fibers are the best sources of short-chain fatty acids to the colon. Resistant starch makes more butyrate than any other fiber tested, but inulin, fructo-oligosaccharide, galactooligosaccharides and pectin also make a lot of acetate. There really isn't a better source, which is why the researchers had to specially make these ingredients in the lab.
Fermentation also = gas
Fermentation does not always mean a lot of gas. Soluble fibers (inulin, fructo-oligosaccharide and galactooligosaccharides) are fermented very quickly because there is nothing to slow it down. In the scientific literature, they report that the tolerance for these types of fibers is 10-15 grams/day, but a lot of people are sensitive to them at doses as low as 5-10 grams, or the amount you can find in a FiberOne bar.
In contrast, resistant starch is insoluble. The natural ones are big starch granules that the bacteria have to eat slowly. The bacteria can only access the outside starch in the big granule, and they have to eat their way through it to get to the middle. As a consequence, resistant starch is fermented more slowly and tends to reach more of the distal colon. This is important because the distal colon is where most of the colon diseases occur - researchers think the diseases occur for lack of short-chain fatty acids. In any case, resistant starch has been reported to have a tolerance of 45 grams/day before there is a statistically significant increase in gas. Unlike soluble fibers, we have never seen anything more than a little bit of gas (bloating, cramping, diarrhea, etc.) in the published studies.
If you are not used to eating fermentable fiber, you should add them slowly to give your body time to adjust to them. People do tend to adjust to them and often gas either goes away or becomes easier to deal with. As you feed the beneficial bacteria, they tend to crowd out the bad bacteria which can be big, smelly gas producers. It all depends on the kind of bugs you have in your gut, which are very individual. Some people get gas no matter what type of fermentable fiber they eat or for how long, while others don't get nearly so much.
Any amount of fermentable fibers that you can get - from foods or supplements - is good.