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There's no such thing as "conservation of matter." There's conservation of mass in basic chemistry, but it's really just a partial understanding of conservation of energy anyway.

It's almost as if the author has never heard of exothermic chemical reactions.

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Conservation of matter is as exact a law as they come in chemistry, let alone biology. The part of mass lost as heat doesn't even match up one part in a billionth. As soon as it becomes relevant, you're not doing chemistry anymore, you're doing physics.

I know it's not "technically" correct, but when doing science, you use the laws applicable to whatever field you're working in.

In biology, there is conservation of matter. Geology, too. Everywhere, really, except in atom-smashers, stellar cores, and nukes.

No, this isn't true. There's no conservation of matter anywhere. If you take 2 hydrogen atoms and weight them, then bond them together in a hydrogen molecule and weight that, the molecule weights less than twice one hydrogen atom.

But you still have the two hydrogen atoms, before and after. They are matter. Tiny (really tiny!) differences in weight don't change that.

I guess when you said "conservation of matter" I interpreted that as meaning "conservation of mass", seeing as we're talking about weight loss.

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