Cheese – How much fat does “low fat” cheese have

Those are called "Eyes" by cheese makers. The appear when bacteria convert lactic acid into propionic acid and carbon dioxide, or metabolise citrate.

These bacteria occur in dairy products, though they can also be added to the curd to get the characteristic eyes. See for example Propionibacterium freudenreichii on Wikipedia.

If you can find a copy, Graham Kerr's "Minimax Cookbook" has guidance and several recipes for low-fat baking. He used to be the galloping gourmet, and produced recipes with outrageous amounts of fat, sugar, and so on. Then his wife had a stroke and he re-examined how he cooks in order to be able to meet her dietary requirements while not losing flavor, texture, and mouth-feel. It covers much more than baking, and is a good guide to low-fat cooking in general. Unfortunately it's out of print (published in 1992), but there seem to be lots of copies available from second-tier distributors.