Baking Powder, Baking Soda, and Yeast

The buttermilk is acidic enough that it interferes with the environment that commercial yeast needs to reproduce well

I don't think this is the case. Yeast prefers a mildly to moderately acidic environment: pH 4.5 - 6 (7 is neutral). The various sources I've found give a pH of 4.1 - 5 for straight buttermilk, and of course that pH is buffered (brought closer to neutral) when you mix it into your dough with the other ingredients. If anything, I'd say that a buttermilk dough would be ideal for yeast growth, provided there's enough water available.

The key difference between baking soda and baking powder is that soda is just the alkali, where baking powder is a mixture of baking soda and a powdered acid, usually tartaric or citric.

You can use baking soda alone with a buttermilk dough because the buttermilk provides the required acid component. For buttermilk pancakes, I like to use a combination of baking power, plus a bit extra soda: Think of it as if the powder reacts with itself, and the soda reacts with the buttermilk (although it's not really separated like that).

So, really any or all of those agents can make a buttermilk loaf rise. The important thing, I think, is that yeast and baking powder/soda have very different effects: not all rises are equal! Powder/soda reacts as soon as its wet, and then again when it gets hot in the oven. It creates bubbles, and that's about it.

Yeast does much more besides. As it ferments the dough it also creates a complex mix of enzymes, sugars, acids and alcohols which affect the flavour, structure and baking characteristics of the bread. The protein structure of the flour changes, and that has a big effect on the finished loaf.

Buttermilk also has some amount of fat in it, which has an effect on bread dough. The fat tends to coat the flour particles, which results in shorter gluten chains - this gives a softer crumb with smaller holes: think brioche vs. ciabatta. You might want to knead or fold your dough more than you would otherwise to compensate for this effect (depending on what you want). My hunch is this is what caught the original author out, not the acidity.

If you're making a typical 'bread', I would just use yeast. The buttermilk will contribute flavour and sourness, and give that texture change I mentioned. If you're just after the tang, a zero-fat natural yoghurt would provide a very similar flavour while affecting texture less.

Unless you're making Irish soda bread (and you should, it's delicious!), I wouldn't bother with powder/soda raising for bread. Yeast does too good a job - save the powder for cakes and muffins!

This website provides nice images that show the contrast between adding extra baking soda to dishes versus adding extra baking powder.

Baking Soda - is sodium bicarbonate. It's a simple base that will react with any acid in your mixing bowl thereby producing bubbles of carbon dioxide. People point to this fact as the reason that it can be used as a leavening/raising agent. The issue with this is that almost every ingredient in your batter is going to be acidic. Even eggs have a pH of 6.4-6.9. What this means is that the reaction is going to start taking place immediately, and those gas bubbles are going to start rising out of your dish. That's why recipes that call for baking soda as the only leavening agent typically have you mix the ingredients together and immediately bake it to seal those bubbles in. What baking soda really excels at is in raising the pH of a dish. This leads to quicker and deeper browning, as it speeds up the maillard reaction. Again, check out the photos of what extra baking soda does.

Comparatively Double-acting Baking Powder has a two-stage heat activated reaction. what this means is that while it'll fizz and make a few initial bubbles it won't release all of its carbon dioxide until it hits 140F in the oven. So it's a more effective leavening agent, especially when you're mixing the ingredients togteher and they're sitting around for any length of time.

Yeast is a different beast entirely- a fungi that breaks down sugars and produces carbon dioxide as a by-product. It needs a longer time to get up to speed since it's a living organism rather than a chemical reaction. Yeast can be great for leavening a baked good, or for adding a yeasty/malty flavour to your baking.

There are definitely some scenarios where it would make sense to add all 3- Baking Soda to help with browning, Baking Powder to add a little bit of lift. Yeast to add a tasty flavour and also aid in leavening.

There are also many other ways to add lift to your dish including aerating eggs and butter before adding them in. Folding ingredients together to preserve their tiny micro bubbles, etc...