I eat a lot less than 1g of protein per pound but still see gains?

most people say you should have at least one gram of protein per pound but i have a lot less than that and still am getting significantly stronger and more developed. Right now i only do push ups, pull ups, crunches, bicep curls, tricep curls, dips, dumbell rows(back), shoulder press, and also jog 5 days per week. I am definitely getting more fit and my arms especially are getting bigger (people have pointed it out) so do i really need to take protein shakes or increase my food intake?