I mean, changing your eating habits is absolutely a form of hacking in pretty much every sense of the word and it can be used to significantly change your life.
Yes, words do evolve over time. Hack originally meant to cut with heavy blows, like with an axe. It then came to mean a clever and unexpected or unorthodox solution to a technical problem. It has since been generalized and adopted by the general population to mean a trick, shortcut, skill, or novel method used increase productivity.
The right diet is absolutely an effective way to increase productivity in life changing ways.
