[p1mrx]

Chemical reactions also lose mass according to E=mc^2, but m is so small that it's hard to notice.

[delecti]

Yup. For example (which I calculated because I was curious), the direct mass conversion equivalent for 2000 food calories of energy is about 93 nanograms. Compare that to the typical value that 1lb of fat is about 3500 calories of usable energy.