We are made of 65% oxygen, 18% carbon, 10% hydrogen, 3% nitrogen. The other 4% are trace elements (including calcium, phosphorous, potassium, sulfur, chlorine, sodium & magnesium). That is about 99.9% of the composition of our body.
Our body uses our ingested energy(food) quite efficiently, that's why we gain weight so easily...
Our thoughts and memories are just a series of many electrical impulses through neurons. You could say our brain is like biological CPU, only more efficient (energy wise) and vastly more processing power.
How's that for Chemistry with a touch of Biology?!
Cheers
Yanoda