Gosh, MS blushes for the first time in months. Thanks. I learned basic biochemistry and nutrition a long time ago, and it took me a while. A summer school biochem intro course got me really interested in nutrition, and I went on to complete a dietetics degree. I quickly realized I didn't want to work in mainstream dietetics, so eventually went on to study biochemistry, then did a M.Sc majoring in genetics, followed by a Ph.D in pharmacology. I drift with the wind, and I'm a knowledge junkie. I am still (23 years on from that first summer school biochem course) totally fascinated by molecular biology/biochemistry. But I can also honestly say that I learned very little of practical relevance in my undergraduate courses, though I loved learning the theory so it was still worth while. I think a basic grounding in biochemistry, followed by an understanding of scientific method and scrutiny (eg when is a rat NOT like a human????) are also pretty valuable. I don't know how you aquire this other than designing your own experiments, writing them up and submitting them for peer reviewed publication (or rejection), though reading lots of scientific papers helps.
Oh yeah, I'm also a bodybuilder and semi-retired PT. I've 'experimented' a little on myself, friends and clients to test what works and what doesn't work for different folks. It's all good fun!