The Mac version of Powerpoint does not and never has supported embedded fonts on either end--it can't embed them, and can't read embedded fonts created by a Windows version. There's no workaround I'm aware of, either, short of installing Windows and the Windows version of Powerpoint in a virtual machine on your Mac, which is pretty extreme (and expensive, unless you already have Windows and Powerpoint licenses laying around).
The workaround would be to either stick to the standard fonts, or (if your presentation doesn't need to be edited by a 3rd party and doesn't include any fancy transitions) export it as a PDF, which includes enough font info to display the text as you'd intended. Incidentally, even if you do have the right fonts, the slightly different font encoding/rendering between the MacOS and Windows can sometimes cause spacing or special character problems even if both people have the font.
I'm resisting the urge to say something disparaging about Powerpoint, so I'll limit myself to the comment that if you're working in Powerpoint and only dealing with English text, there's not a whole lot of need for fancy typesetting beyond what's reliably available cross-platform, anyway.