Atom counts tell a different story from body weight
A body can contain more hydrogen atoms than any other kind and still be made up mostly of other elements by mass. An atom of hydrogen is exceptionally light: its nucleus usually contains just one proton. Oxygen atoms, by contrast, are much heavier, so a relatively small number of them can account for a large share of the body's weight.
That difference is easy to miss because we usually describe the body in grams or kilograms. Counting atoms asks a different question: how many individual particles are there, regardless of how much each weighs?
Why water and fat drive the count
Water molecules each contain two hydrogen atoms for every oxygen atom. Body fat also contains many hydrogen atoms, attached to carbon in long molecular structures. Those molecules are abundant in the body, and each contributes multiple hydrogen atoms to the total.
Hydrogen here is not floating around as the flammable gas used in fuel. It is chemically joined to other atoms in water, fats, and countless other compounds. Its bonds help determine how molecules are built and how they take part in the body's chemistry.
So the striking result depends on what is being counted: hydrogen dominates the body by number of atoms, not by weight. The same body can therefore be rich in hydrogen one way and comparatively light in it another.
