Energy conservation

Conservation of energy i.e. energy is constant; we can only transform it into different forms, but cannot create or destroy it.
We live on food; we eat, digest and then absorb it, in the form of glucose into our cells.
Ever thought of, where all places it goes after getting absorbed in the cells, may be we need it for all our metabolic activities, like exercise, sleeping and working.
What about thought. We think and the byproduct is a thought, but what does it take to form a thought? Few million of cells working around the clock, where the smallest unit of measurement is still not defined!