Question

Why might fatty acids, amino acids, and nucleic acids increase the hydrogen ion (H) concentration of a solution?

Answer 1

they all have the organic acid (ie. R - COOH / carboxyl) group which would dissociate (somewhat) in solution, increasing the acidity of the solution

Explanation:

These are all weak acids, as such their respective Ka (ie. fraction of molecules that actually dissociate into ions that would increase [H+]) would release an incredibly small quantity of hydrogen ions in relation to the quantity that already exist in solution.

I wouldn't expect a significant change in pH of the solution, there would be a small (but measureable with the right instruments) increase in hydrogen ion concentration as a small fraction of the acids ionize in solution.

This site has a good visualization of the carboxyl group; it even mentions amino and fatty acids as examples