Acetoacetate is both a ketone and a carboxylic acid, but the carboxylic acid trumps the ketone in our pigeon holes of naming organic molecules that doesn’t mean a whole lot in reality. The hydroxy part of beta-hydroxybutyrate means it’s also an alcohol, but again, the carboxyl group trumps that, making it also a carboxylic acid. (Most anything that ends in ‘ate’ or ‘ic acid’ is a carboxylic acid.) The beta part means that the hydroxyl group is on the second to last carbon, the ‘first’ carbon has the carboxyl group. As an acid, carboxylic acids lose a hydrogen and become ions with an O- (Oxygen with a negative charge) at the ‘beginning’ end of the molecule. As an ion, it’s named ‘ate’, as a neutral molecule (which never exists at the pH of blood) it’s named ‘ic acid’. You may have heard about beta-hydroxybutyric acid. It’s the same thing, but at a more acidic pH than blood.
We say ketone bodies to mean all 3 (acetone, acetoacetate and hydroxybutyrate) because they’re what you get when you metabolize fats instead of carbohyrates. We get lazy and shorten that to ‘ketones’ but it’s not accurate. Acetone, as the smallest molecule, comes out in our breath and it what is measured when we measure our ‘ketones’ from our breath. Acetoacetate comes out in the urine and is what is measured when we measure the ‘ketones’ in our urine. Beta-hydroxybutyrate is what we measure in the blood. Somehow, ketone bodyogenic diet doesn’t roll off the tongue as easily.
BTW, pet peeve, drinking alkaline (non-acidic) water does absolutely nothing for your health. It’s crucial that the pH (measurement of acidity) of our blood is VERY VERY stable. We have 4 large systems and multiple smaller ones that ensure that our pH remains just right. The two biggest are our kidneys and our breathing rate. For example, if you go up in altitude quickly and have to breathe harder to get enough oxygen, your pH goes off a little until your kidneys can catch up. You get a head ache because your brain (as well as other locations, but they’re not locked into a bony vault) swells and pushes on your skull! That’s why you spend weeks at the various base camps when you go up Everest. If you were to fly all the way up and stay for any length of time, you’d die. The large airplanes could be pressurized to something closer to sea level if they wanted to, but they’re pressurized to 10,000 feet so that walking around takes a little more energy and makes you feel just a little ill so you’ll stay in your seat. Anyone want any more ‘weeds’? 