Yesterday after Mass there was a parishioner who asked me about the difference between fasting and abstinence. Fasting sometimes requires abstinence (not eating meat). I will address them separately.
Fasting is eating less with a purpose. For instance, we fast when we skip a meal or when we eat smaller portions, not as a diet but offering up this sacrifice for somebody or for the intention of somebody. This practice also becomes an intercessory prayer. We fast to be more aware of the presence of God in our lives and our need for him. Our dependence in the Divine Providence is what make us closer to him. Every year as Catholics, we are obliged to fast on Ash Wednesday and Good Friday.
On the other hand, abstinence is not eating meat. We are called to practice abstinence (ages 14 and up) every Friday during Lent. As I mentioned in the beginning, sometimes fasting includes abstinence, but abstinence is not fasting. When we abstain from eating meat, we can eat normal portions but we are just avoiding meat. As Catholics, we are obliged (ages 18 to 60) to practice both. http://www.usccb.org/beliefs-and-teachings/what-we-believe/canon-law/complementary-norms/canons-1252-and-1253-observance-of-fast-and-abstinence.cfm
For people with health issues, there is no obligation to practice fasting. We are called to practice abstinence because we can substitute meat with another kind of meals with protein.
Fasting can be applied to several areas of our lives. We can fast from watching too much TV, the use and abuse of the internet and social media.
As a way to clarify the word abstinence, we can abstain from sex and other pleasures; that is another meaning for abstinence but this way to understand abstinence does have to do with the word abstinence during Lent. Similarly, abstaining from sexual intercourse for a period of time in a marriage relationship can be seen as a way of mortification but also it is the basic meaning of chastity within the marriage covenant. “John Paul II explains that married couples who practice the abstinence required by natural family planning are highly likely to achieve ‘mature purity,’ for they are ordering their sexual lives to the proper goods of sexuality.”
The Priest of the Missing Backpack 