From the EWTN website, it states that it is a "mandatory tradition" for those who wish to follow the Roman Catholic tradition.
They do clearly state that it is a man-created tradition, not a doctrinal mandate and subject to numerous exceptions (age, illness (e.g., diabetic), prison, bootcamp, etc).
http://www.ewtn.com/faith/lent/fast.htm
Can that be translated as "It is a sin to not comply"?
I would note the great common sense closer from the website:
"One final consideration. Before all else we are obliged to perform the duties of our state in life. Any deprivation that would seriously hinder us in carrying out our work, as students, employees or parents would be contrary to the will of God."
And, no, I am not Roman Catholic, and I do have several minor theological differences with the RCC (like picking on freemasons, how silly), but I am tired of knee-jerk RCC-church bashing by people who don't understand their traditions (not that you are doing so).
So, a Nigerian Catholic is sinning for eating meat on a Friday outside of Lent, while God gives an American Catholic a pass? What if the Nigerian Catholic is visiting the US? Does God make him follow the Nigerian rules or the American rules? How about if he is flying to the US from Nigeria on a Friday? Does the Nationality of the Air Line then determine whether God permits the Nigerian to eat meat? I wish Paul had addressed some of these concerns in his Epistles? He would have had to substitute a ship for the plane, but I'm sure we could have figured it out...
Abstaining from meat; Fridays and Ash Wednesday, and fasting; Ash Wednesday and Good Friday, are mandatory. Giving something up; drinking, the internet, chocolate, etc. is voluntary.