In Catholic practice, fasting limits food intake, while abstinence usually means refraining from meat. They are related practices, but they are not interchangeable terms.
A little more context
For Latin Catholics in the United States, Ash Wednesday and Good Friday are days of fasting and abstinence; Fridays of Lent are days of abstinence. The usual fasting obligation applies from age 18 through 59, and abstinence from age 14. Health-related exemptions apply, and Eastern Catholic Churches have their own discipline.
A practical beginning
Check your diocese’s guidance before planning. Do not use a devotional challenge to override medical needs or an eating-disorder care plan. Prayer, generosity and service belong alongside appropriate penitential practices.
Source & further reading
USCCB: Lenten fasting and abstinence (United States) (opens in a new tab)↗Teaching summaries are introductions. Follow the linked Church source for its fuller context.