Let me take this a step absurdly far:

You may be slightly more buoyant (and therefore apply less force on a scale) everytime you breath in. It’s not the presence of air that has this effect, it’s the decrease in density of your total body (mass/volume) that has that effect. (Helium just contributes a fractional more difference in density compared to air, but how much you breath in probably matters much more than what you breath)

Except, maybe not. Because the air you breath in partially dissolves in your blood. Dissolved matter does not decrease density, rather the opposite: it packs tightly into the voids, increasing mass for the same volume.

How much of an effect this has is hugely debatable, probably depends on a dozen biological and circumstantial factors, and this is where my knowledge ends. But it’s fun to imagine.

However, if you can imagine inhaling but holding your breath at the same time, creating a vacuum in your lungs, then yes, you would be more buoyant, even more than inhaling helium, and the scale would read slightly less.