Q. What is the origin of the act of using a fork with the left hand while cutting food and then switching it to the right hand when eating?
A. What you describe is called “American (or zigzag) Style” of using utensils. Instead, you might try the “Continental” style:
Once the food is cut, the knife is kept in your right hand as the left hand lifts the fork to your mouth. The fork is held tines down with the index finger touching the neck of the handle. The fork remains in the left hand.This is an elegant and efficient way to handle utensils, and considerably easier for left-handed people.