How to deal with assertion that the Catholic Church changes teachings?

I have had two people in the last few months, confront me about the Catholic Church. That they no longer belong, because the Church changes it’s mind to often. They both stated about how the Church can say its a moral sin to eat meat on Friday and now it’s not a moral sin. How do I respond back?

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[LIST]
*]Is It a Doctrine or a Discipline?
*]Can Dogma Develop?
*]Can Doctrine Develop?
*]Can the Church change its doctrines?
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