Inulin (The Jerusalem artichoke and the blustery day)

Inulin is polymeric fructose:

Unlike cellulose (another sugar polymer, which comprises such indigestibles as wood), inulin is quite soluble. To you, it's almost entirely undigestible, and so is one of the "soluble fibers" in your diet.

You can find inulin in various plants, such as jicama, onions, and the Jerusalem artichoke. Because of its relative indigestibility, enzymes in your gut often take advantage of its ready availability and digest it. This can increase the population of bacteria in your GI; because of this, inulin is often termed a "probiotic." This is something of a euphemism; an army of bacteria munching away on a ready carbon source are breathing just like you; this means they're producing carbon dioxide, and they do it in spades.

One gram of carbohydrate, if it's metabolized entirely to carbon dioxide, will produce nearly 700mL of CO₂! Considering your average fart is on the order of 100mL, and you might take in multiple grams of inulin from a supplement or serving of Jerusalem artichoke, it can be a noisy polysaccharide indeed.

Inulin is also notable because it's one of not too many sugars with a negative heat of hydration; that is, it releases heat upon dissolving in your mouth. If you eat inulin powder dry (as you might when tasting certain hippie sugar substitutes), you'll notice a pronounced warmth.

The estimable Harold McGee covers inulin and the Jerusalem artichoke in his excellent The Curious Cook, a lesser-read companion to his book, On Food and Cooking.