In a lemon battery, the zinc from the galvanized nail is giving up electrons and transitioning into an aqueous state:
$$\ce{Zn → Zn^2+ + 2e−}$$
While zinc is entering the electrolyte, two positively charged hydrogen ions ($\ce{H+}$) from the citric acid with two electrons at the copper electrode's surface and form an uncharged hydrogen molecule $\ce{H2}$:
$$\ce{2H+ + 2e− → H2}$$
While zinc is a mineral our bodies need, I wouldn't recommend using this as a source of zinc. Also, zinc toxicity is a thing, so without knowing the dose you're taking, you risk poisoning yourself.
Lemon Battery Wikipedia